The Utah VHF Society
Frequency Coordination FAQ

Purpose of this document:

This page was created in an effort to answer some of the most common questions that are asked of the frequency coordinator, provide an understanding of why a frequency coordination body is necessary, to clarify some frequency coordination policies, and to de-mystify the process.

It should be understood that the needs and actions of the frequency coordinator are not arbitrary, but are based on technical knowledge of the systems involved, familiarity with the coverage of many of the involved sites, and past experience with the amateur community in terms of its needs, expectations, and anticipated future requirements.

While every attempt has been made to make this page as informative and clear as possible, it is likely that something was overlooked.  In matters of policy, the ultimate authority is a document called The Policies of the Frequency Coordinator and its interpretation by the frequency coordinator, not this document.  Please note that this page addresses frequency coordination based on the Utah bandplan and that certain frequency recommendations may not apply in other parts of the country.

FAQ Index:
Here is a quick index of topics covered in this FAQ - click to jump to that topic.

"Why do we even have frequency coordinators, anyway?" Back in the early part of the century, radio pioneers Marconi and DeForest tried to use radio to relay results of a boat race to two competing newspapers. The Interference between the two stations was so bad that neither one had much success. It became clear that for two transmitters to operate at the same time, they needed to operate on different frequencies with adequate spacing between them. Thus began the science of frequency allocation and spectrum management. 

The FCC doesn't assign particular frequencies to amateurs. In day-to-day operation, amateurs simply listen to a frequency before transmitting to assure it is available. But for some kinds of stations, notably repeaters and some fixed auxiliary stations, it is almost mandatory that they operate on fixed frequencies. The remote locations of these stations and the need for filters using cavities make these stations hard to operate on changing frequencies. Additionally, for users to find them, their frequencies must be constant and well-known. 

The problem of finding frequencies for repeaters and auxiliary stations so they do not interfere with each other is given to a frequency coordinator. In the early days of repeaters, frequency coordinators simply made sure that stations close enough geographically to have an "overlap zone" used different frequencies. As available frequencies filled up, frequency coordinators effectively gained authority to say that there is no space for a proposed system on a particular band. When several amateurs vie for a single available frequency, a frequency coordinator may have to make choices based on which proposed system will provide the greatest benefit to the largest number of amateurs. 

"How does someone get to be frequency coordinator in the first place?" The Utah VHF Society was formed in 1968 to promote the installation and use of VHF/UHF repeaters in the state of Utah.  Part of this task involves being a coordination body which operates as a central clearinghouse for information on the usage of the VHF/UHF spectrum within the state, as well as functioning as an arbitrator to help prevent/resolve disputes that occasionally arise. 

The office of Frequency Coordinator is an elected one, chosen yearly at the election meeting.  For the past several years this meeting has occurred immediately after the annual swapmeet which is usually held in February or March.  Although it is not required by the bylaws, the frequency coordinator should be someone who possesses a reasonable degree of technical skill and have the resources to make informed coordination decisions. 

It should be pointed out that the legitimacy of established frequency coordinating entities has long been established in the eyes of the FCC:  As spelled out in FCC section §97.201 (see below) the actions of the frequency coordinator carry weight in disputes.  For several decades now, the Utah VHF Society has been recognized as the official Amateur Radio Frequency Coordinating entity by the ARRL and other national coordinating bodies, and it is through such affiliation that recommendations by the VHF Society Frequency Coordinator pertaining to disputes that may arise tend to be strongly considered.

For a recent example of this the FCC's working with frequency coordinators to help prevent/resolve disputes, read the article FCC Commends Band Plans in Enforcement Letter.

"My repeater broke/quit working/was struck by lightning/buried in snow and will be off the air for a while.  What do I do?" One of your first orders of business should be to contact the Frequency Coordinator, IN WRITING, and explain:
  • What parts of your system are off the air.
  • When it happened.
  • What happened.
  • When you expect to have it back on the air.
The Frequency Coordination policies clearly state that if the frequency coordinator has not been notified within SIX months of a repeater's going inactive, the frequencies will be subject to reassignment.

Please note that you are expected to either return your system to operation in a timely fashion or relinquish the frequencies if you have no further plans to do so!

If there are extenuating circumstances that may explain delay in notification or return of the system to operation, the frequency coordinator will consider these on a case by case basis.

"What are these 'Bandplans' that I keep hearing about?" Although the FCC has already defined specific portions of each band for use with specific modes, there exists a need, in a somewhat less formal manner, to further divide the bands according to the types of operation encountered in everyday operation.  While these "band plans", unlike the FCC's defined segments, do not carry the weight of law behind them they are an integral part within the framework of a number of widely recognized "gentleman's agreements" that, by general consensus of the occupants, play a large part in determining which operations may occur and where. 

For more information, go to the UVHFS Utah VHF/UHF Bandplan page.

"Why in the heck are Utah's 70cm repeaters 'backwards' from everyone else?" In most parts of the country, UHF (450 MHz) repeaters operated by government and commercial entities use a "Low-Output, High-Input" split:  That is, they use a positive offset. 

Many areas (including Utah) are different:  The standard is to use a negative split (i.e. "Low-Input, High-Output") - and for good reason.  In the early days of 70cm repeater operation, it was immediately noted that the best sites for locating repeaters already had existing UHF transmitters on-site.  Because commercial users use a positive offset, their transmitters were (in some cases) just a few hundred KHz above the top of the ham band. 

This provided a very good case for avoiding a positive split on the amateur frequencies:  Placing a repeater input just a few hundred KHz away (or even a few MHz) from a UHF transmitter (like a multi-hundred watt 454 MHz paging transmitter) was just asking for trouble.  Using a negative split for the amateur repeater places the receiver an additional 5 MHz farther away, making co-location with commercial users more practical.

"I want to put up a repeater with a phone patch at my house.  Gimme a frequency." Unused repeater pairs, especially 2 meter repeater pairs, are virtually nonexistent in all metro areas in the country. The Wasatch front is no exception. 

Occasionally, a repeater pair will become available by attrition (the owner/trustee moves away, loses interest, dies, and no one takes over) and/or by mutual agreement to implement protection measures such as tone access, directional antennas, site location chosen to intentionally limit coverage.  If frequency sharing is to be considered, all parties agree, in writing, to accept the potential of some degree of interference from each other as well as spell out the responsibilities of the parties involved and the means by which these problems are to be resolved. 

Unfortunately, pairs don't become available very often on 2 meters (and, increasingly, on other bands as well.)  For this reason, in fairness to the largest number people, when a repeater pair becomes available (on any band) first consideration is given to those who can put the repeater in a location that will benefit the greatest number of people and/or provide a service and/or demonstrate a technology that has the potential of furthering the art of communications.  Quite frankly, a limited-coverage repeater at someone's house with a closed phone patch doesn't fulfill this requirement.

"I have already bought/was given/stolen a repeater.  It is worth a lot of money!  You must give me a frequency now!" WRONG!!!

You just can't buy a frequency - and spending a pile of money on a bunch of equipment isn't going to create a frequency where none was available.  True, you may have better equipment and/or location than other repeaters that are on the air, but that doesn't enable one to exercise any sort of "eminent domain" on someone else.  If you find yourself in this unfortunate situation, you have several choices: 

  • Put yourself in the queue and wait for a frequency to become available.  You might be able to put it on a Test Pair in the meantime.
  • Put it in such a remote location that there are frequencies available in that area.
  • Help another individual/club upgrade an existing repeater.  Granted, for many, having their own repeater is an ego boost, but wouldn't it be better to improve a repeater that people already use?  (There are already too many repeaters with lousy coverage that people don't use!)
  • Sell the equipment and get at least some of your money back!
"I have listened on xxx MHz and I haven't ever heard anything.  Can't I put my repeater there?" Just because you can't hear anything on a particular frequency doesn't mean that it is not being used.  Especially if you are using a handie-talkie, you may just not be able to hear it.  It's possible that you may be able to hear something on that frequency just across the valley. 

Even if you can't hear anything anywhere in the valley with state-of-the-art equipment it doesn't mean that the frequency can be used without interference. Repeater site A may not be able to hear a trace of repeater B and vice-versa, but if there's an area somewhere between the two where users can access both sites, it may not be practical  to share the frequency. In other words, the places where you have to check aren't just where you are going to put the repeater, it could be somewhere totally unexpected and not just in the midpoint between the proposed site and the nearest existing one on the same frequency. The experience of the frequency coordinator (and others) can be invaluable in determining the suitability of various sites in this respect. 

If you do find a frequency that you think can be shared, and if you can come to some agreement (in writing!) with the other potentially affected user(s) of that frequency as to how you can implement a frequency-sharing plan, and the plan is a sound one, then some serious consideration will be given to the proposal.  Frequency re-use plans that are carefully considered and implemented are encouraged by the frequency coordinator.

"Who is hoarding all of these frequencies, anyway?" They aren't being hoarded.  Owing to geography, usage patterns, specific monitoring location, the use of subaudible tone, or the fact that the repeater may be temporarily off the air, a frequency may appear to be vacant when, in reality, it is very much in use.  Keep in mind that there are locations in the valley where it is possible to key up a repeater on almost every pair on 2 meters! For a list of all 2 meter and 70 cm repeater pairs and how they are being used around the Wasatch Front, go to the "2 Meter Repeater Pair Utilization along the Wasatch Front" and the corresponding 70cm pair utilization page.

Another thing: Before you consider a frequency too strongly, make sure that it is actually in a repeater subband! (Yes, coordination requests like that are frequently received...)

"On 2 meters, we could put more repeaters on the air if we went to a 15 KHz spacing, right?" This is an oversimplification of the problem.  As it turns out, you cannot put two repeaters only 15 KHz apart and have usable results unless you take certain steps: 
  • The repeaters need to be geographically separated from each other.  That is, they must be far enough apart that their respective coverage areas do not have significant overlap.
  • Tone access is usually necessary to minimize the effects of interference from those users in the overlap areas that would potentially cause problems with the repeaters involved.  (On the subject of subaudible tones, read this!)
  • The repeaters that are adjacent (in frequency) may need to be alternated in the split direction.  This is one of those factors that would need to be implemented only upon careful consideration of the specific case.
What does all of this mean?  If the population base were spread out all over the area, that would imply that the repeaters were also spread out over a large area and you could get enough distance between repeaters to allow 15 KHz spacing with careful spectrum management.  Situations like this exist on some of the flatter, more densely-populated states in the east and in some parts of California. 

In Utah, that is definitely not the case:  The vast majority of the population lives along the Wasatch Front.  Furthermore, there are only a limited number of sites that have reasonable coverage (i.e. atop a mountain) and so the existing repeaters tend to be located in clusters.  Finally, since they are atop mountains, they cover large geographical areas and are thus poor candidates for the 15 KHz spacing.  In the 80's when there was a big push to adopt either 15 or 20 KHz spacing, the VHF Society carefully considered both options.  Upon changing to a 15 KHz spacing "on paper" it was soon discovered that if 15 KHz spacing were to be adopted, it would allow fewer repeaters along the Wasatch front than the 20 KHz spacing! 

By the way, are you wondering why, for example, the 146.61 repeater on Abajo peak does not seem to fit in the Utah bandplan?  That's because it doesn't!  Because of its remote location and proximity to Colorado, it has been worked into Colorado's bandplan, which is 15 KHz.

"I notice that repeater frequencies like '146.85' and '145.40' aren't being used.  Can I put my repeater there?" The simple answer is no, as Utah is on a 20 KHz bandplan.  The nature of FM does not allow two channels 15 KHz (or closer) to each other to be used simultaneously without mutual interference.  In areas (such as California) where they use 15 KHz channel spacing they have to go through great pains to permit 15 KHz channel spacing (see the above Q&A about 15 KHz spacing.) 

If you did put two repeaters just 10 KHz apart (even if one was relatively weak at a particular location) there would be enough splatter to open the squelch of a receiver on either channel (both the repeater's receiver and the user's receiver!  And no, running subaudible tone is not the answer!)

(If you still think that adding a subaudible tone will help, you should read this first.)

"I'm looking at the VHF Society repeater list and I see some repeater 'test pairs' marked 'SNP.'  What are those for?" There are several so-called "Shared, Non-Protected test pairs" (SNP) that are set aside for special purposes.  Some uses of these pairs might include: 
  • A temporary repeater to provide needed coverage for an event or a state of emergency.
  • The evaluation of a potential repeater site to determine its viability and coverage for a specific area. Its use is often pending the availability/accessibility of a site or a frequency pair.
There are some restrictions on these "test pairs:" 
  • They are not to be used for permanent operation.
  • There may be more than one repeater on this pair in a given area so the frequency of the tone access and/or antenna patterning and/or site selection will have to be considered on a per-case basis.
  • Users must be prepared to deal with possible interference issues as they arise.
  • All repeaters using test pairs must utilize subaudible tone access.
  • It is the responsibility of each user on each test pair to stay informed of the activity of others using that pair. This is necessary because of the shared (unprotected!) nature of the coordination.  If possible, this information will be made available online.
  • The availability of the test pair may be limited in those areas of Utah where the coverage of the proposed operation may impact those in adjacent states.  That is, the test pair isn't available everywhere.
Just like any other repeater pair, use of the test pair must be coordinated.  This is necessary to keep the frequency coordinator (and others) informed of the activities on the frequency and to make sure that each repeater that may be on the test pair uses its own unique subaudible tone. 

Along the Wasatch Front, all new 70cm and 2 meter repeaters are initially placed on one of these test pairs.  Why?  As it turns out, most proposed repeaters are never built!  In the past, when repeater pairs were more readily available than now, a pair was simply assigned to these "paper" repeaters.  At one point, years ago, there were nearly as many "paper" repeaters as real ones - and it's an unfortunate truth that trying to reclaim long-unused pairs often resulted in resentment as the holder perpetually "still planned to put it on the air..." Assigning proposed new repeaters to the SNP allows testing of the repeater - if it is ever built - but does not tie up valuable spectrum if it isn't. 

The available test pairs are as follows: 

  • 10 meters:  No test pair available
  • 6 meters:  53.210 (output) 52.210 (input)
  • 2 meters:  145.410 (output) 144.810 (input)
  • 220 MHz:  224.86 (output)  223.26 (input)
  • 70 cm: *  449.250 (output) 444.250 (input) 
  • 23 cm:  1283.000 (output) 1271.000 (input)
  • 33 cm and above 23 cm:  Contact the frequency coordinator
* - The 449.250/444.250 pair is not available as a test pair in central Utah.  As with any repeater operation, contact the frequency coordinator before ordering equipment or going on the air on any amateur frequency!
"If you can't coordinate simplex frequencies, then why can you tell me what I can't use for simplex operations?"
You may be wondering why, if frequency coordinators deal only with "coordinated" frequencies, why they have any business dealing with "simplex" frequencies at all?  First of all, one must remember that one of the primary duties of the frequency coordinator is to keep track of the uses of all amateur VHF, UHF, and Microwave frequencies to make sure that chaos doesn't result from ill-considered operations.  Closely related to this is to make certain that those operations that do occur on the bands in question are, in fact, compatible with the other operations that occur on that same band.

Clearly, not all possible needs can be accommodated by our limited amount of spectrum, so a combination of common sense, technical savvy, and cooperation is required in order to allow as many users to peacefully co-exist on the band as possible.

When it comes to simplex operations, one must realize that frequencies may be coordinated if they are not listed in repeater lists.  Why is this?  It is because that it is not only repeaters that are coordinated, but so are control, auxiliary, and special-purpose links - and it is not necessarily in the best interest of the operators of those systems to publish certain details of their operation.  One reason for such apparent "secrecy" would be for an inter-system link - that is, one that ties one repeater to another:  It is often the case that in a system of this sort, direct access of the system by an uninformed user on this frequency would, in fact, disrupt the system.

For this and other reasons, a close relationship is maintained between the frequency coordinator that the person who is keeping track of local simplex usage see the "Simplex Frequency Manager" on the UVHFS Simplex Frequency Usage page.:  Because both people are familiar with the technical aspects of radio communications and the types of systems that are using the various frequencies, it is best that those who need to request additional frequencies keep close contact with them.
"What is the deal with these 'Coordinated' simplex frequencies?" Believe it or, there is really only one "coordinated" simplex frequency on 2 meters and it is 146.52.  This is a de facto coordination that provides for a common frequency on which contacts may be made. 

While simplex frequencies are not coordinated, they are assigned to various groups.  Most of these groups are localized and thus it would make little sense for them to use a wide-area coverage repeater (assuming that there were enough repeaters to accommodate them in the first place.)  By publicizing the use of various simplex frequencies by these groups, potential conflicts (such as scheduling of nets as well as interference issues) may be minimized. 

This list of simplex frequency usage is the basis of "gentleman's agreements."  It is a matter of courtesy that one would refrain from using a frequency during the scheduled activities of a particular group.  Likewise, it would be improper for anyone to discourage the use of a frequency by anyone other than a member of the group to which the use of a particular frequency is attributed.  Remember, the amateur radio frequencies are a shared resource! 

If it is determined that use of a frequency results in interference with another group or to a coordinated system, it is imperative that the frequency coordinator be notified immediately to facilitate resolution!

For a list of Wasatch Front simplex frequency usage, click hereIt should be noted that this list of simplex frequencies is managed by John Mabey, W7CWK and is subject to review (and revision) by the frequency coordinator.

"I have a mobile/portable repeater that I want to set up.  Give me a frequency." For the reasons outlined above, assigning a full-time repeater pair to a user that will only be using that pair on rare occasion can hardly be justified.  For this reason, one of the "test pairs" may be assigned for the occasional mobile/portable use. 

It is in the best interest of the amateur community that these mobile/portable repeaters are just what they claim to be:  That a "temporary" mobile/portable repeater is not to turn into a permanent one!  If possible, information on who is using a test pair (and where) will be made available online.

"I want to leave my radio on the 'Crossband Repeat' mode for (some event.)  What frequency can I put this on?" Many radios have the ability to function as a crossband repeater where signals are automatically received on one band and retransmitted on another, usually between 2 meters and 70 cm.  Generally when these radios are operated in this manner they are configured to retransmit what they hear on 2 meters on 70cm and can switch automatically to retransmitting what they hear on 70cm on 2 meters. 

Unfortunately, they are rarely operated legally!  Most radios capable of crossband operation cannot automatically perform the function of a legal ID:  In most cases, it may not be possible (or practical) to ID the link in both directions as required.  (Note:  YOU may be identifying your station as you transmit through the crossband to, say, a repeater, but your crossband may not be identifying legally as it retransmits the repeater on another band.)  Additionally, the FCC rules require that some means of control be implemented in the event the repeater needs to be shut down (such as in the case of a malfunction that causes interference to another repeater or radio service.) Remember that most radios in crossband repeat mode will be stuck in transmit as long as there is a signal on the other band's input and in that state remote control, if available, may not even be possible.

It is possible to operate some radios as a remote controlled station instead of a repeater.  In that case, you can remotely operate a radio that is transmitting/receiving signals from one band to another and it can be argued that this is not a repeater.  It should be remembered that this is only the case if there is, in fact, a definite means of remote control on a frequency on which it is legal to do so.

Assuming that the operator has taken the trouble to provide a legal ID and control mechanism in the case of a crossband repeater, there is often the tendency of many crossband repeater operators to forget that the device they are operating is a repeater and may be operated only in the repeater subbands! 

"Where can I operate my simplex repeater?" A simplex repeater is a "store and forward" device.  That is, it operates on just one frequency and, when it hears a transmission, it records that transmission and at the end of the transmission it plays back what it "heard."  Typically, these repeaters have 20-30 seconds of recording time (much more makes them very tedious and awkward to use...)  As in the case of crossband repeaters (mentioned above) the frequency coordinator considers that they really are repeaters and must be operated in a repeater subband. 

Some suggested operating frequencies on 2 meters include those in the 146.42 to 146.58, and 147.400 to 147.58 area, avoiding the most heavily-used 146.52, 146.54, 147.42, 147.54, and 147.60 MHz simplex frequencies.  Always listen before using a frequency and make yourself aware of regular users - and let them know what you plan to do.  To prevent the simplex repeater from being an unintended nuisance and potentially making the frequency unusable to any others, configure the system such that a subaudible tone is required for access.

A WORD OF WARNING:  The FCC rules could be interpreted to regard a simplex repeater in the same manner as a full-duplex repeater.  If this is the case, the repeater must be operated in a portion of the band in question where repeater operation is allowed.  For example,  a simplex repeater may not be operated below 144.500 MHz or in the range from 145.5 to 146.000 MHz. 

The rules also state that, for repeaters,  some means of control is required.  This could be a person at the repeater site, or some electronic/remote means of control.  Because of some recent "incidents" involving simplex repeaters, it has become apparent that not all simplex repeaters are equipped with a means of remote control - or even an automatic IDer!  In these recent incidents, it was the intention by the repeater's operator to be able to manually control the equipment and/or manually ID, but in these cases he/she simply forgot to shut the equipment off or left it on when they were unable to quickly return to the control point.  In these cases, the identity and location of the now-interfering simplex repeater was unknown, owing to complete lack of an automatic ID.

If you are able to set up a simplex repeater so that it can be operated lawfully (e.g. with ID, appropriate control, etc.) any of the suggested simplex frequencies where repeaters may be legally operated can be used (aside from the most popular ones such as 146.52, 146.54, etc.) and that you are certain that its operation will have minimal impact on those who already monitor/operate there.  You should also configure any simplex repeater to use subaudible tones so that casual or random operations on the frequencies involved don't activate the repeater. 

"Where can I operate my simplex Echolink/IRLP/whatever node?" These days, it is common to read/hear about people who have connected their radios to the internet providing virtual linking all over the known universe.  Typically, this is done using Echolink or IRLP - although a number of other similar systems exist.

There are a number of "high profile" IRLP systems - such as the full-time links operated by WA7GIE and the IRLP node on the 146.76 repeater that is open to UARC members.  These offer excellent, wide-area coverage for both "conventional" repeater users and those connected via the internet and are connected to high-reliability links.

It is also common for people to want to put up their own "private" Echolink or IRLP nodes - but there's a problem:  These usually are NOT associated with a repeater and, therefore, the frequency of operation cannot be readily "coordinated" owing to the widespread use of all simplex frequencies on 2 meters and many simplex frequencies on the 222 and 440 MHz bands.  For this (and other) reason(s) it is recommended that simplex node operation NOT be carried out on 2 meters as this band is so heavily-used by a lot of different groups.

Why not "coordinate" such frequencies?  This has not been traditionally done as amateur radio operators are free to choose their own operating frequency - with the possible exception of currently-coordinated repeater frequencies - the latter authority having been granted by the FCC to bona-fide coordinating bodies:  In case you didn't already know, the Utah VHF Society is, in fact the "bona-fide" coordinating body in Utah!

Simply plopping a node on any old simplex frequency - especially on 2 meters - is NOT a good idea - and for several reasons:
  • As noted before, a number of groups regularly use simplex frequencies for scheduled activities such as nets or general simplex coordination.  Around the Wasatch Front, the most commonly-used frequencies include 146.52, 146.54, 147.42 and 147.54.  If a node is dropped onto such a frequency - and it goes active in the middle of, say, a net - you will not make any friends and you may get a friendly postcard from the local Official Observer reminding you of proper operation of your amateur station!
  • Sometimes people pick "bad" frequencies.  Below 146 MHz, all operations occurs on "odd-10 kHz" multiples, such as 145.11, 145.51, etc. while 146 MHz and above, operations occur on "even-10 kHz" multiples such as 146.52, 147.54, etc.  Picking a frequency "in-between" is a very bad idea as it ignores the fact that receiver are, in fact, about 20 kHz wide:  If you picked, say, 147.43, you would not be operating on just 147.43, but your signal would be splattering onto 147.42 and 147.44, making operating on those to frequencies impossible!  Again, doing this may get get you a postcard from the Official Observer!
  • Watch band allocations!  Sometimes people operate in the low 144 region or in the 145.8-146.0 region and both of these are a NO NO!  The bottom of the band above 144 MHz is reserved for CW and weak-signal operations and you may actually get into legal trouble (you read about that when you studied for your license, right?) and the 145.8-146.0 is reserved for satellite operations - and operating there will make enemies over multiple states... and likely get you a postcard!
  • It has been interpreted that unattended node operation on a simplex frequency is, in fact illegal.  Unattended, automatic operation is only legal on certain frequencies in the amateur bands to start with - but even such legal automatic operation is subject to certain restrictions related to control of the transmitter!  If you are planning to operate a simplex node at all, you MUST be present at some sort of control point and monitoring the activities whenever it is active!  This requirement may sound onerous - and for some people, it is - but it is a requirement of such operation!  There have been many instances where stations operating unattended in this manner have earned themselves a letter from the FCC asking where the control operator was when things went "wrong"!
So, where can you operate a simplex IRLP/Echolink node?  If you are along the Wasatch Front, probably NOT on 2 meters.  If you do use 2 meters, it would be best if you are able to coordinate such activity with the group(s) that regularly use the frequency chosen.

If you wish operate a node on a simplex frequency, you should:
  • The Simplex Frequency Manager may be able to provide an assignment of a 70cm simplex frequency for your simplex operation.  Please note that these frequencies are shared, but usually on the basis of geographic separation so that there will be minimal interaction between users with typical installations at their homes.
  • Is yet another node really needed?  There are a lot of nodes sitting around doing nothing - many of which disappear due to lack of interest.  What will your node do that others won't do?  Is this a node just for your own personal/family use - and if so, is that really an appropriate use for a valuable resource such as a frequency?
  • Again, you should make sure that you are aware of regular usage of the frequency being used.
  • Always be in earshot of what's on frequency.  Keep in mind that nodes can come up random when online and easily land on top of a QSO in progress!
  • You should NEVER run a subaudible tone squelch on the simplex node's receiver!  In the event that a node appears - say, in the middle of the net - having an unknown subaudible tone selected can make it impossible for those operating the net to ask for the person coming over the node via the internet to stand by until the net is over!  Essentially, running a subaudible tone on a simplex node is like blindly transmitting with your receiver's volume turned down and not listening before transmitting - which is illegal in most cases!
After reading the above, don't assume that the answer will be "no" - but be prepared to scale your expectations appropriately and to do some due-diligence to make sure that you aren't going to make a lot of people mad at you and that you won't be running afoul of the law!
"I've got an idea:  Can't we re-use the same frequencies if we all run really low power - like the cell-phone people?"
In the world of cellularized communications systems (such as cell/PCS phones, and many emerging data networks) the re-use of frequencies is made possible via the use of, among other things, transmitter power control

This is not a new idea:  FCC §97.313(a) clearly states that "An amateur station must use the minimum transmitter power necessary to carry out the desired communications."  This decades-old rule makes sense, as not only is excessive power wasteful, but has the increased probability of causing interference to other stations on the same or nearby frequencies.

With the increased pressure on spectrum, commercial entities (such as wireless telephone companies) have also capitalized on this idea - and taken it to further levels:
  • The "Base" station is in constant communications with user's transmitter, making certain that it transmits just enough power to maintain acceptably noise free and/or error free communications to maintain a reliable circuit.  In addition to allow good frequency re-use, it maximizes the user's battery life by only running the lowest power needed.  (Note:  This is also why one gets best battery life if one always extends the phone's antenna - and why those without extendable antennas often have poorer battery life than those that do...)
  • The "Base" station also uses directional antenna arrays.  Doing so allows additional re-use of frequencies owing to the fact that signals coming from directions other than the one from which the user's transmitter is arriving are rejected to some degree.
  • The "Base" station uses specialized timing/coding to minimize interference.  In today's digital world, wireless telephone services are almost entirely digital, and in doing so, this allows additional re-use of frequencies where it was not previously possible.  This is done by very careful selection of digital coding (to minimize inadvertent "correlation") as well as carefully-controlled frequency and timing offsets to minimize the probability of interfering energy from other users.  This is done in addition to all of the other schemes mentioned here.
  • The "Base" station uses geographical separation in conjunction with frequency re-use.  Before frequencies are re-used by other sites and users, one must make certain that the BOTH the Base Station and the User are going to use frequencies that are least-likely to cause interference with the other users and base stations.

While, at first glance, it might seem that such schemes could be implemented via amateur radio, this is only partially true:
  • Amateur Transmitters' power outputs are NOT automatically controlled.  Without a continuous feedback mechanism from the "other end" it is impossible to know exactly how much power one needs to run to have "just enough" power to communicate.  But, there is another problem that one must consider:  A wireless telephone is communicating ONLY with its base, and this analogy falls apart when you are trying to compare it with a situation where one simplex station is trying to communication with several other stations.  If this analogy were to work properly, you would need to know how much power to run to be heard by the worst case station - and to know this, you'd need to know how well every station was hearing you.
  • In most cases, when trying to operate over a fairly small geographical area - such as for short-range simplex operation - the use of directional antennas is simply not practical, as there is a good probability that the users could be scattered about in all directions!
  • On current amateur radio, we are still using FM for communications.  While it is possible for the stronger FM signal to "win" when placed in competition with a weaker one, the MUCH more likely result is that neither one will be easily copied.  Some of the newer digital communications schemes, however, are so-devised that several signals of equal strength on the same channel may be individually distinguished.  While there are some emerging amateur standards that use digital modulation schemes, it should be pointed out that NONE OF THEM are designed to operate in a similar manner, mostly owing to the requirement that significant infrastructure needs to be established to support those highly-complex digital schemes:  Because Amateur Radio is intended to be, among other things, a last-resort, self-sufficient communications service, having such an infrastructure could be considered to be a potential weakness in times of calamity.
  • When it comes to geographical diversity, the wireless telephone operators have several advantages over hams trying to engage in multi-station simplex communications:
    • The locations of the base stations are fixed:  Cell sites really don't move around much.  When a new site is established, it is done only after careful analysis and consideration of impact on neighboring sites.
    • Wireless telephones talk ONLY to the base station, and not to each other!  If you are talking to another user, you are always doing so via the base station.  This is most unlike amateur simplex communications where each station on a geographical area can talk to each other directly.
    • Wireless telephone systems will, on-the-fly, assign (and even switch) frequencies to best-suit conditions as they continually change.  If a user is moving around, both frequency and power will be automatically adjusted as necessary to minimize the possibility of interference.

As can be seen from the examples, while frequency-reuse on amateur frequencies is possible, it is a simple fact that the extent to which this may be done is limited by our system topology - which includes several important things:
  • The geography along the Wasatch Front.  The Provo-Salt Lake-Ogden area is almost a worst-case scenario for a wireless telephone system designer.  Why?  In an ideal (flat!) world, the radio signals would go only a few miles before being stopped by buildings, foliage, and the curvature of the Earth.  In this area, we are confined to a bowl-shaped valley, where most locations within the valley can see almost everywhere else in the valley.
  • There are very wide local variations in terrain which may make it more difficult for some users to hear each other.  In many instances, most users can hear each other with relatively little difficulty, but there are some users who may live in lower areas (within canyons, behind hills, etc.) and it may be necessary for some of the other locals to run additional power to be heard by those people in less-than-optimal locations - and when this extra power is used, their signals will certainly carry further - especially if, as is likely, those same people are in "good" radio locations to begin with!
  • Recognition of the situation and the ability to be able to do something about it.  Many volunteers have only a vague familiarity with the radio equipment that they are using.  Even if they are experts, they cannot be expected - especially during communications - to constantly monitor their transmitted power or try to determine how well other people are hearing them in order to minimize their transmitter power.
  • It is important to remember that it is not an easy matter to predict exactly how much power is required to cover a given distance.  For example, it takes only about 0dBm (1 milliwatt) of radiated power (from a clear location) to put a relatively noise-free signal into a typical mountaintop 2-meter repeater or to cross the valley in a clear line-of-sight path.  On the other hand, it may take several watts of power in order to maintain reliable communications between two sites that are only a few miles apart when terrain (or buildings) intervene - and one must NOT forget that each of those two sites requiring watts of power may, in fact, have a good path to an even more distant location:  Clearly, one (if not both) stations could disastrously impact communications that was being attempted at this distant location on the same frequency.
  • Finally, consider that many modern cellular telephones have a tremendous power control range, typically from 300 mW (1/3rd of a watt) at their highest power level down to a a few microwatts (a few millionths of a watt) - a 100,000 to 1 range, or about 50dB.  Most radios have a rather limited range of power control - about 10:1.  Consider a rather common circumstance:  You are trying to communicate with another station located, line-of-sight, only a few hundred yards away.  For such a short distance, it only takes a few millionths of a watt to provide a solid link over that range - but most HT's can only be lowered to 1/3-1/2 watt - which is (literally) tens of thousands of times more power than is necessary - and is hundreds of times more power than may be necessary to get into a distant repeater - assuming a reasonable antenna and a clear, line-of-sight shot.

Again, remember that it is NOT a good idea to attempt to use subaudible tones on simplex frequencies in an attempt to achieve frequency re-use!
"Nobody owns a frequency.  Why can't I operate wherever I choose?" While it is true that no amateur owns a particular frequency, the FCC rules state the following: 

- Section §97.201 of the Amateur Service rules: 

(c) Where the transmissions of a repeater cause harmful interference to another repeater, the two station licensees are equally and fully responsible for resolving the interference unless the operation of one station is recommended by a frequency coordinator and the operation of the other station is not. In that case, the licensee of the non coordinated repeater has primary responsibility to resolve the interference.
This clearly gives the party that is operating a coordinated system priority over those who are not - a fact re-emphasized by recent FCC enforcement action. 

This does not address the use of those non-repeater operations that aren't coordinated, such as various simplex frequencies.  Since the amateur service is largely self-policing, there are a number of "gentleman's agreements" that offer recommendations and provide guidelines as to what may be operated where.  It is in all of our best interest to follow these guidelines as well as the recommendations of the frequency coordinator.  If a dispute should arise that, for whatever reason, cannot be resolved by the parties involved, it is recommended that the frequency coordinator be consulted for adjudication.

"If no-one owns a frequency, then why are there these 'closed' repeaters and/or autopatches?" This can be a point of contention for some.  While it is true that no-one owns a frequency, there are some repeater owners/operators that wish to limit the access of their repeaters to a certain subset of the amateur population (such as club members.) 

The cases where this may be so includes: 

  • Linked repeater systems:  Since these systems cover such a large area, and because of the (often) high costs associated with the upkeep of such systems, regular usage of these systems may require membership in the affiliated organization.
  • An autopatch: Often, a particular repeater may be open to all amateurs of appropriate license class, but an autopatch on that repeater may be restricted to members of the associated club/organization.
The reasons for these restrictions could be one or more of the following: 
  • These systems are expensive to install, operate, and maintain.  Restriction of these resources to members of the sponsoring organization is a valid means of providing the funding, experience and human resources keep these systems operational.
  • The nature of the system may require than certain procedures and etiquette be followed.  A large, linked system should be used with the consideration that its coverage allows for a very large number potential users.  An autopatch will often have specific procedures that need to be practiced.  Membership in the affiliated group has the benefit of providing training in the use of these systems.
Even though completely closed systems are arguably contrary to the spirit of amateur radio, it should be noted that the FCC has affirmed the right of repeater owners/operators to place reasonable restrictions on the usage of their systems.  Keep in mind that a repeater is not a natural resource. It is owned by some person or group and it is imperative that we respect the policies that the repeater operators institute.
"Why have subaudible tone (a.k.a. 'PL') access on a repeater?" In the amateur radio tradition of cooperation and public service, most repeater operators strive to make their repeaters available to everyone.  (There are a few exceptions, such as linked repeater systems, etc. that strongly encourage membership - for more information, read the section above.)  In light of this, repeaters have traditionally operated COR (Carrier Operated Relay.)  That is, the repeater is activated if there is a signal present. 

Unfortunately, COR can be activated by any signal - even ones that are not supposed to be there.  Most of the repeaters in the mountain west are located on sites with good vantage points such as mountaintops and ridges.  By necessity, these sites are often crowded with many other radio users.  It is an unfortunate fact that, when multiple transmitters are co-located, some "mixing products" occur.  These products (also known as intermod) can be created in the receiver itself, in other transmitters, in metal-to-metal contacts of nearby structures, and conductors, to name a few.  There are also those occasions when a nearby transmitting system may be malfunctioning (or just of poor design) and radiating signals on frequencies where it should not, or any combination of the above. 

In an ideal world, these other transmitters (and receivers!) would all operate independently of each other and not cause any sort of QRM.  Unfortunately, this is the real world.  Noise, spurious emissions, and intermodulation products do get created and they do get into other systems.  As population densities increase and radio sites become more and more crowded, these problems are becoming increasingly more common. 

While good system design will minimize these sorts of problems (and that's assuming that those sharing your site have designed their systems well) but not always will they be completely avoided.  If everything has been tried (as far as reduction of interference is concerned) then the last choice may be to make the repeater tone-access only. 

It should be remembered that adding tone access will not solve the problem, but it may mitigate it.  A common scenario is that a repeater will work perfectly most of the time but occasionally, it will start squawking, making noise, and key up (kerchunk) at random.  A repeater that does this, even occasionally, is very tedious to monitor.  This is a case where it might make sense to put tone access on a repeater.

All of the above applies to digital tone-signaling schemes (such as DPL) as well!


When a subaudible tone (a.k.a. "PL") is a bad idea:
It is unfortunate that some repeater operators have the mistaken notion that adding tone access will solve all of their problems.  There was a local case several years ago where the owner of a 2 meter repeater installed a subaudible tone decoder on his repeater and was disappointed to note that the repeater still functioned badly:  He had not addressed the actual cause of the repeater's poor performance (in this case it was  desense and the ensuing intermod resulting from a mistuned duplexer and/or bad antenna.)  The repeater seemed to sound better (it didn't kerchunk on its own, squeak or squawk) but it was still a lousy repeater in that no-one could get into it. Remember:  Adding subaudible tone access may simply be masking other problems.

As with other aspects of repeater operation, tone squelch operation (including frequency) should be coordinated with the Frequency Coordinator.  This helps the Frequency Coordinator maintain accurate records and, in cases of frequency re-use issues, prevents the same tone from being assigned to two repeaters with potential overlap issues.  Furthermore, this allows accurate tone information to be made available for publication (if this is desired) in repeater directories and databases. 

Finally, when a tone is needed, it is recommended that a 100 Hz tone be used where possible.  This is the ARRL recommended frequency for open repeaters with tone access.  In this area, 88.5 Hz is commonly used by the ARES groups while 123 Hz is used by the Ogden group.  Keep in mind that there are a few people that have radios that are capable of only one tone frequency (for all channels) and that the use of many different tones may complicate the programming of already difficult-to-use radios and the plethora of tones makes access to these repeaters more difficult. 

One other instance where tone access may be desirable is to minimize the effects of repeater overlap.  As an example, there are two 146.34/146.94 repeaters in Utah:  One is located atop Farnsworth Peak, just west of Salt Lake City, and there is another one on Frisco Peak, located north of Cedar City in the southwestern quadrant of the state.  These repeaters are quite distant from each other, but there are a few points (in the middle of the desert around Delta, Utah and in various parts of Utah county) where it is possible to access both repeaters simultaneously.  As rare as this is, it was decided that each of these two repeaters should be equipped with subaudible tone access (different frequencies, of course) to reduce the effects of a user's operation into one affecting the other.  Remember that if you are accessing two repeaters at once, part of the burden is for you to do what you can to reduce this interference potential:  This might include cessation of operation, operating at a lower power, changing location, or using a directional antenna.

It should be important that the use of tones on repeaters is a decidedly different technical issue from using them on simplex frequencies:  In the case of repeaters, the interference potential amongst the repeaters and the groups of users is well-known.  In the case of simplex use, the fact that users' geographical location may be random and the fact that simplex frequencies are expected to be shared makes the use of tones (or digital codes) on these frequencies a bad idea! (Read the next topic for more info on the use of tones on simplex.)

"What about using subaudible tones (a.k.a. 'PL') to allow more people to 'share' a simplex frequency?" Several years ago, someone decided that, if the different local groups using the same simplex frequency all used their own subaudible tone frequencies, that this frequency could be "shared" and all of these different groups could use this same frequency at once without the different groups hearing each other.

They were right - these groups were no longer hearing each other.

The problem was that a lot of the people trying to talk amongst themselves in these groups could not reliably hear each other, either!  Why?  It's the nature of radio (and, in particular, FM) communications:  The strongest signal will always win - tone or not!  If the strongest signal that "captures" your receiver doesn't have "your" tone, you will hear absolutely nothing!  The same is also true of signals that are of "approximately" equal strength as well:  Neither signal will be clearly audible due to the interference and any tones (or codes) cannot be properly decoded!

A common occurrence in this situation was as follows:  One station was receiving the tone-encoded transmission from another station.  Suddenly, the signal seemed to disappear for a few seconds - and then reappear.  What happened?  Another signal of the same or stronger strength appeared on frequency - but without the tone frequency for which your receiver was set - and covered up the other station.  With the tone missing, corrupted, or invalid the receiver faithfully muted the speaker.

What about "Digital Squelch" systems?  Again, the issue is not trying to find a "unique" code to tag a transmission, but the fact that signals of similar strength will simply obliterate each other:  This obliteration (unintentional "jamming") will make any coding that you may have applied irrelevant!

Tone and digital squelches are not conducive to the sharing of simplex frequencies!

Perhaps a more important reason for not using subaudible encoding/decoding on simplex frequencies is that it goes against the very notion of sharing a simplex frequency:  If your subaudible tone decoder is active, you cannot hear any other activity on that frequency and if you transmit, there is a good chance that you will disrupt their communications as well!

Read the previous topic for info as to why a tone is OK on a repeater.

"It sounds to me like getting a repeater on the air is tough.  How do I go about actually getting one on the air?" No-one said that it would be easy.  Here are some things that you should keep in mind and some questions you should ask yourself if you are serious about putting up a repeater: 
  • Will this repeater offer anything that one (or more) current repeaters in the area doesn't already offer, or will this just just end up being your own private repeater at your house with limited coverage and a closed phone patch?  If so, perhaps you might consider offering your support to an existing repeater to make it better.  Perhaps you can put your proposed repeater on one of our bands that should see more activity?  Maybe your proposed repeater can demonstrate a particular technology that will further the state of the art of amateur radio.
  • Are you willing to commit time and money to put a decent repeater on the air?  If you had to buy the parts new, even the simplest repeater can cost more than $1000 to get up and running.  Certainly, by keeping an eye out for good deals and being willing and able to modify radios, you can cut costs considerably.  If you are indeed fortunate enough to be able to locate this repeater in a desirable location (such as a mountain top or an unusually good valley location where its coverage will be useful) that often means that some site rental needs to be paid and access to the site will be severely limited.
  • Do you have technical expertise to be able to assemble and maintain such a system?  If not, putting up a repeater is a very good way to learn, but you should be prepared to seek and consider advice from a mentor.
  • Chances are that people will associate this repeater with you!  If, for example, the audio sounds terrible, the repeater is deaf, noisy, producing spurs (and other interfering signals,) or it is down much of the time, (that is, its a lousy repeater!) you are responsible.  The continued upkeep and proper operation of any repeater is ultimately the responsibility of the licensee.
  • You should read the "So you want to put up a repeater?" page.
"I done some 'figgering here, and it looks like I can shoehorn in a repeater/link if it uses a split that is opposite everyone else's on that part of the band.  Can I do this?" Generally speaking, putting a reverse repeater pair in amongst the rest of the repeaters is not a good idea.  For one thing, most users are at "ground level" - that is, their simplex coverage is rather limited as compared to that of a mountaintop repeater, so their signals to a repeater's input are going to be relatively limited in their coverage area.  A repeater, on the other hand, is often located where it will offer the best coverage for the area intended - and that may overlap other repeaters that may be on the same frequency and quite far away. 

If the two repeaters share the same output frequencies, then they don't really "know" of each other's existence (i.e. they will not cause interference to each other, although those people that happen to be in overlap area(s) will likely experience some interference) because their output frequencies are the same.  Take these same two repeaters and invert one of them so that the output of one is the input of another, and vice-versa, and you can have some real problems.  If there is the slightest chance that they will "hear" each other, then one will need to put a subaudible tone encoder on the inputs to prevent feedback, for starters.  Additionally, if one of the repeaters is transmitting and (even weakly) gets into the other repeater, it will effectively "desense" that repeater, making it useless for repeating weak signals that are intended for it - and tone access will do nothing to prevent this problem.  (Read this to learn of an instance where tone access was a bad idea...) 

If both of these repeaters are on mountaintops, say, it is likely that they will have to be 200+ miles apart from each other (in many cases, even farther!) to keep such repeaters from bothering each other.  Additionally, it must be remembered that there are occasional (but not extremely rare) tropospheric propagational enhancements that may cause paths between such repeaters suddenly improve dramatically (just ask a VHF/UHF weak-signal person!) or appear when no previously known path was known to exist. 

In any event, placing an upside-down repeater pair amongst other repeaters necessitates much wider geographical spacing of the repeaters on that frequency - making that frequency unavailable for any use (or re-use) over a much larger area than with a conventional split. 

Occasionally a "reverse" pair seems ideal for linking two sites together.  If this link is not acting as a repeater, per se, the above considerations need to be recognized in appropriate context:  If you are operating a hub-and-spoke system (such as the Intermountain Intertie or the SDARC system) then you may have sufficient justification to "tie up" a pair over an already large area.  Recognize, however, that there are some instances where it may be more advantageous to link a system on another portion of the band (the 430 or 420 portion, in the case of 70cm) or on another band entirely rather than "hog" a pair. It should be noted that in these sorts of systems, directional antennas are often used. 

In short, while there may, on specific occasions, be definite technical merits of using an inverted pair, it generally does not lend itself to the most efficient spectrum use.

"D-Star will save us all!!!  We should be putting up D-Star repeaters everywhere, right?"
A lot has been said about D-Star recently.  If you don't already know, D-Star is a digital radio system, capable of carrying both voice and data, that includes networking and messaging capabilities and at the time of this writing, D-Star radios are available only from Icom.  D-Star uses a proprietary (e.g. secret) voice encoding/decoding scheme called AMBE:  Because of its proprietary nature, "open-source" versions of this codec are not available.  This voice data stream is then carried on a data stream that uses an open, published protocol that allows for control, identification, message-handling and routing - amongst other features.

Others have successfully been able to retrofit other radios by adapting an Icom D-Star module intended for other Icom radios and interfacing it with an analog radio using a simple computer interface.  It is also worth mentioning that a few have bought the proprietary AMBE codec chip from DVSI (the owner of the intellectual property rights associated with AMBE) and made their own interface device or have used a "D-Star Dongle" - a device that includes the DVSI codec that can be attached to a computer.  Most of these "alternate" means of generating/receiving D-Star are beyond the means of many amateurs, however.

It should be noted that the voice compression used in D-Star is somewhat similar in its operation to the voice compression used in digital cell phones, satellite telephones, and VOIP telephone circuits.  Because of the heavy amount of compression, the subtle qualities of the voice are noticeably altered - particularly in the presence of strong background noise.
  • For an audio clip providing a comparison of normal analog and D-Star, click hereThis audio clip (260kB) provides a demonstration of how "pretty good" signals sound using analog and D-Star, with no decoding errors in the D-Star stream.  Evident in this recording are the effects of the audio compression on the voice quality.
Additionally, as signals degrade due to fading and/or interference, one doesn't necessarily hear noise with D-Star, but rather odd-sounding artifacts - or perhaps nothing at all - when the decoder is suddenly unable to make sense out of what it is receiving.
  • For an audio clip demonstrating what happens when both analog and D-Star signals are degraded due to multipath and weak signals, click here.  This audio clip (260kB) provides a comparison of how analog and D-Star signals behave when conditions worsen.  Both signals were generated "live" and consecutively using the same transmitting and receiving gear.
While D-Star uses less spectrum than a standard, narrowband (+-5 kHz deviation) FM voice channel, as currently implemented using Icom radios, the reality is that, once considerations have been taken to avoid co-channel interference in light of the disparate signal strengths normally encountered in real-world situations, about 1.5 D-Star channels will fit in the space of just 1 "normal" 20 kHz 2-meter voice channel:  While demonstrations have been made showing up to three D-star channels operating in a 20 kHz bandwidth, more rigorous examination has shown that in order to maintain signal integrity when very strong and very weak signals are present on adjacent channels (e.g. >30dB of signal difference) that broader spacing is required to maintain acceptable operational margins.  (It is worth noting that D-Star consumes more spectrum and is somewhat less power-efficient than ACSSB, an analog scheme proposed in the early 90's that was to be used in the 220-222 MHz portion of the 1.25 meter band that was removed from the amateur service.)

The digital nature of D-Star - despite its intrinsic error-correction capability and tolerance of signal degradation - should not excuse the system designer from considering the limitations of this - or any - system in the analog/RF domain.  Because of the nature of this and other digital systems, signal degradation due to interference, multipath, path loss, or dropoff in transmit or receive system performance can be masked:  Unlike with analog systems, casual observations of the D-Star signals being "heard" may not provide many clues as to the problems leading to system degradation - that is, it is difficult to discern whether signal loss is due to a weak signal, multipath, or interference from another source - say powerline noise, spurs from a computer, or intentional interference.  Another consideration is that, at the time of this writing, there are relatively few tools available to the maintainer of a D-Star system to aid in the diagnosing of system problems:  Existing test equipment is of limited use in the determination of overall system performance and the diagnosing of problems.  The semi-proprietary nature of the D-Star system (e.g. the "closed" nature of the AMBE voice coding plus the fact that, currently, only Icom is supplying gear) makes it unlikely that D-Star specific test gear is likely to be available soon, although that doesn't rule out possibility of the modification of existing D-Star radios or adapting the use of existing analog test gear to provide some of this functionality.  (The Utah VHF Society has produced a web page with information about using analog test gear for analysis of D-Star systems  - it may be found here.)

One of D-Star's potential strengths is its digital nature.  D-Star's original intent was to allow for a network of linked systems - connected locally or via the internet - that could allow users to talk to each other from anywhere in the world.  This network is growing and various practical challenges imposed by peculiarities of the original design of the open-sourced linking protocol are gradually being addressed.

The Utah VHF Society is looking closely at D-Star and other emerging digital voice and data technologies.  One of the challenges is to provide spectrum for the testing, evaluation, and operation of these types of systems without significantly impacting more "traditional" operations.  Despite the very crowded conditions on 2 meters and 70cm, effort has already been made to provide spectrum for some of the first systems to be put online.

If your group wishes to put a D-Star system on the air, here are a few things to remember:
  • Remember that the codec used in D-Star is proprietary and unless you really like to build your own gear and have the time and ability to do so, you will have no choice other than Icom for your radios or repeaters.
  • Digital systems such as D-Star offer the system designer the possibility of flexible networking of radio systems operating over large geographical areas, including routing of voice and data.
  • It should be noted that D-Star repeaters will generally repeat any D-Star signal through them, regardless of what is set in the callsign field!  This is done so that any D-Star radio listening to that same repeater will be able to detect if someone is transmitting on the input, reducing the possibility of "doubling" with another station - even one that may not be an "official" member of the local community.  Note that if this repeater is connected to a larger network (either via radio or the internet) then only those appropriately-addressed signals will get passed along into the network cloud.
  • Do not expect that D-Star will supplant conventional analog systems anytime soon.  Unlike certain commercial and federal mandates, there are currently no outstanding requirements for bandwidth reduction technology to be used on Amateur Radio bands.
  • Existing repeater owners are not going to be "evicted" in favor of D-Star!  Remember that there are little-used repeaters on the air and it is possible that their owners may be amenable to relinquishing those in favor of systems may be able to provide better service to the amateur community and public.
  • Remember that, on 2 meters, simply replacing an analog repeater with a D-Star repeater isn't really saving any spectrum as only one D-Star repeater can actually fit within a 20 or 15 kHz channel and still maintain adequate margins to offer protection to and from adjacent analog channels and the D-Star channel!  At present, the best economy of spectrum can be obtained by locating several D-Star systems on adjacent frequencies to allow the recommended minimum 12.5 kHz spacing.  (See below for channel spacing recommendations.)
  • When deciding to co-locate a D-Star system amongst or adjacent to (an) analog system(s) one must remember to consider both the occupied bandwidth and the receiver bandwidth of  both the analog and digital systems - see below for more information about this.
  • Before ordering any D-Star repeaters or radio systems, please get in touch with the frequency coordinator!  Putting a D-Star system on the air is arguably more difficult than an analog system.  He/she can offer advice as to what works and what does not as well as putting you in touch with others who have had experience.
  • Remember:  It is not expected that D-Star will be the only "new" digital or analog system to be considered for future use!  If you have a proposal for a "non-traditional" usage of the VHF/UHF/Microwave bands in Utah, please feel free to discuss it with the frequency coordinator.
For more information about the spacing requirements between D-Star and analog signals, continue reading below.
"Yaesu has its own digital audio system that is sort of like D-Star.  How is it different?"
More recently than D-Star's introduction, Yaesu has introduced their version of digital voice for the VHF and UHF amateur bands.  While it uses the same type of audio codec as D-Star, it uses a different form of modulation allowing twice the data to be sent in less than twice the bandwidth.  What this means - in theory - is that it should be possible to obtain better weak-signal performance than with D-Star since more bits may be sent to provide error correction.  This also means that more data may accompany digital voice transmissions if so-desired.

While D-Star uses a modulation form called MSK (Minimum-Shift Keying) at 4800 baud, the C4FM signal used by Yaesu - and other commercial digital audio communications systems - uses four separate levels which means that for every "baud", two bits may be sent rather than just one as is the case for MSK which means that the C4FM system used by Yaesu conveys 9600 bits per second of data as compared to D-Star's 4800 bits per second.  For a variety of technical reasons, the bandwidth occupied by this C4FM signal is comparable to the average bandwidth of an analog FM voice signal - which is to say that it is a bit wider than a D-Star signal.  Being that it is digital, however, it doesn't have the occasional "bursts" of wide bandwidth associated with voice peaks found on a typical FM signal so the level of adjacent-channel interference is much more consistent and thus it is more likely that it could be made to co-habitate at 15 kHz channel spacing than an analog FM voice signal.

Yaesu's implementation has two voice mode:  A "wide" digital voice mode and a "narrow" digital voice mode.  On the air, they take up exactly the same bandwidth as the difference is related to how much of the 9600 bits per second being sent is dedicated to voice.  In the "wide" mode, more bits are used for voice so the audio quality is quite good - very noticeably better than that of D-Star.  In the "narrow" mode, however, the bit rate dedicated to voice is much lower and the audio quality noticeably reduced - perhaps slightly worse than that of D-Star - and in that mode one can send much more auxiliary data on the transmission along with the voice payload.  Interestingly, testing has shown that the "narrow" mode appears to tolerate data errors better than the "wide" mode and thus has an approximate 1dB weak signal advantage while still retaining intelligibility.

At this point it is not known if/how the digital audio signals from the C4FM signals may be routed on the internet in the same way as voice is.  It is worth noting, however, that unlike D-Star, there is much easier access to the "analog" side of the world so that it is theoretically possible that a Yaesu digital repeater could interface directly with the older analog-interface linking systems such as IRLP, D-Star or Yaesu's own WIRES system.
"D-Star is digital so its audio quality and range has to be better, right?" D-Star uses a lossy voice codec:  The term "lossy" means that at least some of the information in the original audio has been discarded in order to reduce the amount of bandwidth (e.g. number of bits) required to represent some semblance of the original sound.  The higher the compression, the lower the bit rate, and the more information has been thrown away. 

It is important to be aware of the effects of this "lossy" compression on speech, however.  D-Star uses a class of codecs referred to as "MBE" or MultiBand Excitation - specifically AMBE (Advanced MultiBand Excitation,) a proprietary codec developed by DVSI.  The MBE codecs work somewhat differently from other, more-familiar audio compression schemes such as MPEG, in that they are more-specifically designed to reproduce speech.

In a nutshell, the codec takes advantage of the fact that human speech consists primarily of two types of sounds:  Voiced sounds (a fundamental frequency and its harmonics - as in vowels) and unvoiced sounds (such as consonants) that are more-or-less unvoiced bursts of noise.  Simply put, the codec decides of the sound is voiced, and if so, it decides which of the harmonics are present and their relative amplitudes;  When an unvoiced sound is produced by the user, it analyzes the properties of the noises.

This sort of codec is quite good at mimicking human speech - even at very low (lower than 5 kbits/second) bit rates.  As you might guess, as the bit rate is lowered, the representation of the original voice sounds become less precise as more information about the original voice is discarded.  A very serious problem of intelligibility arises with these low-rate codecs in the presence of extraneous noise:  As the amount of non-voice sounds added to the speech increases, the codec has increasing difficulty in proper reproduction of the speech, as there's often no way for the codec to "know" what is speech, and what isn't, plus the codec's limited data bandwidth becomes more occupied with trying to reproduce increasingly complex combined sounds:  This has the inevitable result that the precision of the reproduction of the speech degrades noticeably.  When this happens, the codec itself can produce truly odd artifacts when it mistakes the extraneous noise (or the combination of extraneous noise and a voice) for speech!

Note:  Most current public-safety implementations of digital voice systems operate at a coding rate higher than that used by D-Star and often include additional noise-canceling techniques that are applied prior to final encoding.  This has the implication that the lower coding rate of D-Star makes it even more susceptible than the systems used by the public safety users to the deleterious effects of extraneous noise on speech intelligibility.

This problem has become tragically apparent in the public safety field where there are numerous examples of fire fighters, policemen, and other safety workers having had their lives put in jeopardy (or lost!) because of a breakdown in communications due to various quirks in the modern, narrowband digital voice systems.  These incidents have related both to the topology of the system (the fact that they require end-to-end communications through a trunked system rather than having the option of something like simplex that allows in-situ, direct unit-to-unit communications) to the "digital cliff" problem (that is, the inability to determine the actual quality of the RF signal in order to determine how reliable the radio link is) to the breakdown of the speech codec itself due to extraneous noises, such as those from sirens, nearby engines, or even speech muffled by a breathing apparatus:  These problems have been increasingly apparent as the use of the digital systems has become more widespread, causing a number of public safety agencies to put the brakes on the rollout of new systems, or revert back to the old, analog systems.  Recently, there has been talk of putting a halt on the FCC-mandated rollout of these narrowband systems until these problems have been successfully addressed.

While it is unlikely that many of these instances would affect the amateur radio operator to the extent that they impact public safety workers, it is well worth keeping apprised of these issues and the lessons learned.  These lessons include the effects of extraneous noise on the intelligibility of transmitted speech, plus providing education to the user of a digital system about the "digital cliff" that is encountered at the fringes of the digital system's communications range.

See also:
For a report about the testing and implementation of digital voice systems by various public safety agencies, look at these links:

"D-Star is digital so it doesn't bother analog users, right?"

or

"D-Star is digital, so it can ignore analog users, right?"

or

"To save space, we can use both both analog and D-Star on the same channel because they won't bother each other, right?"
WRONG!!!

One who tunes in a D-Star signal on an analog receiver will hear in  "buzzy" noise and by just listening to this "noise" the user of an analog receiver will not be able to determine who it is that is transmitting.  Remember that a D-Star signal will interrupt and jam an ongoing conversation of those using an analog mode.

Likewise, if an analog signal appears on the same frequency as a D-Star signal, it is likely that the D-Star receiver will simply mute - or, possibly, give a few odd-sounding syllables, grunts and noises as it tries to make sense out of the mess - and D-Star signals are more easily "damaged" and rendered unintelligble by an analog signal than an analog signal by a D-Star signal!

In either case, you cannot operate D-Star and Analog signals on the same frequency and expect them to co-exist in a practical manner.  D-Star users have an advantage, however, in that they can program their receivers to detect the presence of an analog signal on the same channel.

This situation is not unlike the use of subaudible or digital-coded squelch on simplex frequencies:  Operators doing so may have the illusion of privacy or even the mistaken notion that such operation allows improved sharing, but this is not the case!
"Because D-Star/C4FM/APCO P-25/Mototrbo is digital, you have to use special gear to 'DF' it, right?"


No!

There are two general types of DF (Direction Finding) techniques:
  • Signal strength.  These use the strength of the signal - often using a directional antenna such as a Yagi - to determine the direction from which the signal is arriving.
  • Phase-detection techniques.  These include systems such as two-antenna "TDOA" or the electrically-rotated antenna ("Doppler") systems that can, in one of several ways determine something about the direction of the incoming signal.
Clearly, the "signal strength" system doesn't really care what mode is being used:  As long as the signal can be detected in some way, one can determine its direction - even if the receiving device can't make sense out of what it is "hearing" as would be the case if using an analog receiver to track down a digital audio signal.

For the phase-detection systems, it turns out that many of the systems designed for analog reception will work with a digital audio signal as well, although the "bandwidth-limited noise" nature of the D-Star/C4FM and other digital audio signals may reduce accuracy and sensitivity of some units somewhat - depending on their design and filtering.

Even the signal modulation of these digital audio modes is "digital" in its nature, it is still just an analog signal so one would continue to use the same analog receiver as before in conjunction with the signal meter or direction-finding unit.  Of course, if one wanted to "hear" the audio being transmitted on the digital signal being tracked you would need to use a receiver capable of receiving that digital mode on a separate antenna to do so.
"D-Star is digital and so much narrower than analog that we can put a whole bunch of them in the space of one analog signal, right?!"
There has been some mention of how spectrum-efficient D-Star is as compared with analog signals and how several D-Star signals can be crammed into the same space as one analog signal:  One oft-cited instance is the simultaneous operation of several D-Star signals spaced only 6.25 kHz apart from each other.  While this sounds like an impressive feat, cursory examination of the bandwidths of the transmitters, receivers, and link margins will immediately reveal that this is NOT a good thing to do!  (It is worth noting that some Icom radios cannot tune in 6.25 kHz steps anyway, requiring a minimum channel spacing of 10 kHz anyway  - see below.)

As it turns out, as of the time of the original writing of this article relatively little had been done to carefully analyze how D-Star signals will co-exist with each other - and with existing analog signals - in the real world, using real radios that people own.  In order to answer some of these questions, we decided to make some careful measurements using typical radios.  Details of such measurements may be found on this page:

Link:  Utah VHF Society D-Star channel spacing recommendations

Based on the test data as well as frequency and spectral analysis, the following are recommendations of the Utah VHF Society:
  • D-Star to D-Star channel spacing:  12.5 kHz minimum
  • D-Star to Analog channel spacing:  15 kHz minimum
On 2-meters, the above recommendation is complicated by the fact that the channel spacing in Utah is 20 kHz - something that does not readily lend itself to the adoption of 12.5 kHz spacing.  This has two important implications:
  • Several D-Star systems should be placed on adjacent frequencies.  If two consecutive channels are available (a total of 40 kHz) that means that a total of 3 D-Star channels might be placed within this space and still provide protection of adjacent analog channels from interference.  Given the current heavy usage of the 2-Meter band, careful coordination will be required to find contiguous spectrum.
  • A single D-Star signal may be placed where there was an analog signal.  Unfortunately, in this situation, one cannot take advantage of the spectrum-conserving capabilities of D-Star.
On 70cm, with 25 kHz analog channel spacing, it is perfectly reasonable to place two D-Star channels within one analog channel:  One D-Star signal would have a center frequency 6.25 kHz below and the other 6.25 kHz above the center frequency of the channel, but please note the warning below about the inability of some Icom radios to tune in 6.25 kHz steps.  This means that D-Star channels must be placed on multiples of 12.5 kHz - which also means that one must have multiple, contiguous 25 kHz channels in order to provide 12.5 kHz channel spacing that does not interfere with adjacent analog channels:  This also means that at the top and bottom edges of this contiguous space, a 6.25 kHz wide "half channel" is wasted as the 12.5 kHz centers of the D-Star channels must align with the spacing of the analog channels!

Remember:  The above are minimum spacing recommendations.  Depending on the specific situation, there may need to be other considerations based on the necessity to protect existing and proposed systems.

A word of warning:  Some Icom D-Star capable radios (such as the IC-2200H) cannot tune in 6.25 kHz steps:  When considering channel frequencies, choose carefully to make certain that you do not inadvertently exclude users by selecting frequencies to which their radios cannot be tuned!

For 23cm DD (128kbps) mode operations, the currently-recommended channel spacing is 500 kHz - read here for more information about this recommendation.
"Yaesu's C4FM digital voice is as narrow as D-Star and we can pack more of those channels in too, right?" Newer than D-Star, Yaesu's own digital voice format using a modulation type called C4FM - which stands for 4-level FSK - has a digital voice codec that operates like that used by D-Star - but it is not compatible with D-Star.

Rather than using plain old FM (MSK, actually - which is a special case of FM) Yaesu has chosen a modulation scheme in which two bits are sent per baud rather than just one with D-Star.  What this means is that the baud rate used by D-Star and Yaesu's C4FM are the same, the latter, sending two bits per baud means that the raw data rate for the C4FM is 9600 bits per second as opposed to D-Star's 4800 bits per second.  What this means is that in the "Digital Wide" mode, much better audio fidelity is possible with the Yaesu implementation than with D-Star as most of the bits being sent are dedicated to voice.  In "Digital Narrow" mode far fewer bits are used for sending voice and the audio has a more "compressed" sound than in "Digital Wide."

In order to preserve the signal integrity as much as possible, C4FM's bandwidth is comparable to a narrowband voice channel which means that the receiver bandwidth is about the same as that used for standard +/- 5 kHz deviation FM signals.  In measurements of C4FM signals it has been determined that the -6dB bandwidth is on the order of 8  kHz, the -20dB bandwidth is approximately 13 kHz and the -40dB bandwidth is about 18 kHz:  Please note that these measurements are relative to a modulated C4FM carrier using a 300 Hz resolution bandwidth which means a similar comparison to an unmodulated carrier would yield "better" numbers in terms of occupied bandwidth.


In measuring the bandwidth of a Yeasu C4FM receiver it was found to be approximately 13 kHz wide at the -6dB points, 16 kHz wide at the -20dB points and 19 kHz wide at the -40dB points which makes it comparable to that of a standard (perhaps somewhat narrow) FM receiver intended for +/- 5 kHz analog FM.

What this means is that one would coordinate and space C4FM signals in much the same way as +/- 5 kHz deviation analog FM signals.  Considering that like D-Star, C4FM's modulation is quite consistent as compared to FM which can have transient peaks of wider bandwidth from the voice energy, a digital signal like this is likely to be a better neighbor than an analog signal!  This also means that it is more likely that one could successfully put two C4FM signals 15 kHz apart than you could two analog FM signals!
"Once my frequency is coordinated, it is mine, right?" Remember:  No-one owns a frequency.  To prevent valuable spectrum from being tied up needlessly, there are several limitations on frequency coordination.  For example: 
  • Frequency coordinations are initially issued for a three month period.  It is during this period that it is expected that construction/installation of the system is to occur.  If, for some reason this is not possible, it is the responsibility of the entity to which the coordination was issued to inform the frequency coordinator, in writing, of the reasons why the system was not completed and, as appropriate, request an extension  Otherwise, the coordination will be canceled.  It is highly recommended that the frequency coordinator be kept informally apprised of the progress being made by telephone, email, or by letter. 
  • Once the coordination goes into actual use the frequency coordinator must be notified, in writing, to that effect.
  • Any proposed major changes (location, antenna type, transmit power, etc.) will require re-coordination.  Remember:  A given coordination is done on the basis of the technical information available at the time of coordination.  If the coordination was made in the basis of a frequency-sharing agreement, for example, consent of all parties involved and a technical evaluation of the changes must be conducted to assure adequate protection.
  • Additional conditions apply.  For more information, see The Policies of the Frequency Coordinator.
"What's this about 'Frequency Sharing?'  How can one 'share' a repeater frequency?" Actually, frequency sharing is done all of the time in other places.  On HF, for instance, frequencies are re-used all of the time.  As an example, numerous groups could use the same frequency on 75 meters during the daytime and, if they were far enough apart (daytime signals on 75 meters only cover a area of several hundred miles radius) the groups would never be aware of each others' existence.  Likewise, in the commercial radio world, frequency sharing of VHF/UHF frequencies and their re-use is the rule rather than the exception!  (Cellular telephone operation, for example, is an extreme example of such re-use!)

Effective sharing on VHF/UHF requires a bit if forethought, however.  Clearly, one would wish to avoid the placement of two systems on the same frequency in the same town (unless, of course, the two owners of the systems can come to some agreement as to how this is to be done...) but re-use by multiple systems separated geographically can work, provided that a few thinks are taken into account: 

  • What is the nature of the systems involved?  If, for example, the two repeaters are intended only to offer local coverage - and their coverage areas are, in fact, limited by geography and/or system design, then it may be possible have two systems on the same frequency in (nearly) geographically adjacent areas.  Clearly, two systems located atop mountains with huge overlapping coverage of population areas would not be a good idea.
  • In systems where there are some areas where minor overlapping coverage is a possibility, the use of subaudible tones is required and the frequency of these tones must be coordinated.  The use of tones will prevent inadvertent access of one system by a user of the other system sharing the frequency.
  • Occasionally, directional antennas may be part of the system requirement.  If, for example, your system provides good coverage of your intended area - but it also has some "spotty" coverage in some other direction that may be a potential problem, it may be necessary to provide some directionality to the antenna system.  Generally, if the "problem area" is in a direction other than that of the main coverage area, addition of a directional system will only improve coverage in the intended area due to stronger signals, better apparent sensitivity, and reduction of potential interference.
  • Frequency sharing may be used to advantage of the two systems are linked to each other full-time.  In these situations, the amount of overlap may be increased - the amount depending on various parameters - and one can, in effect, provide a "virtual" system with coverage over a larger area.  Doing this requires some attention to technical detail, but the frequency coordinator will be glad to assist you in this matter.
  • At the frequency coordinator's discretion, a written agreement between all parties involved in the frequency sharing/re-use may be required.  The purpose of this agreement is to spell out, beforehand, what the responsibilities of each party are should interference issues arise.
Being the "real world" it is likely that problems may arise when re-use occurs.  In light of this, there are several things to keep in mind: 
  • There just aren't that many "clear" pairs available on our 2 meter and 70cm bands.  (Depending on your intended coverage area and band, there may not be any at all!)  If your needs are for a repeater with a very localized coverage area, then you will be assigned a pair that is to be shared with another repeater.  Normally, the owner/users will never experience any interference problems in their intended coverage areas, but the possibility exists that overlap will occur.
  • The coordination of a repeater applies only to the intended coverage area.  For example, if you have a repeater on a rooftop in Provo, you can only expect coverage of Utah County.  The frequency coordinator will make every attempt to make certain that coverage in Utah County is not compromised by a repeater in an adjacent area.  However, if that same frequency is re-used in Ogden (with a coverage area of Davis and Weber counties) it is likely that there will be areas in the Salt Lake valley where both repeaters may be accessed.  Because this is not in the intended coverage area for either repeater (and is, in fact, a "buffer area" between the two systems) it will be up to the repeater owners themselves to take care of any interference problems that might result if a user in Salt Lake insists on using one of the repeaters.  The use of subaudible tones or directional antennas (on the part of the user in the overlap area) will generally mitigate the problem.
"I need frequencies for my emergency services group - give me some!"
One of the most important aspects of amateur radio is that of community service:  This is, in fact, one of the key justifications for the very existence of amateur radio and its use of valuable frequency spectrum and such use is spelled out in the FCC rules in the portion known as the "Basis and Purpose" and you may have even heard people refer to amateur radio-related community service as "paying the rent."  To aid in this aspect of amateur radio, there are a number of groups that organize and provide training for amateur radio operators to serve in these roles.  This nature of these organizations and training is widely varied, but it almost always includes structure and technique for effective communications under different and adverse conditions.

It should come as no surprise that for training and organizational purposes, many of these groups have certain frequencies on which they conduct their activities.  Often, these groups use a combination of repeaters (their own or, with permission, existing repeaters belonging to other groups) as well as simplex frequencies to facilitate these communications, organizational and training activities.

It should also be recognized by members - and especially, organizers of these groups - that the radio spectrum is a very limited resource and its use requires the careful coordination of the activities of many diverse groups to avoid conflicts that might impede the effective communications.  Practically speaking, there are simply not enough frequencies for each group to have their "own" frequency!

While it might seem to a good idea if each group had its "own" frequency, this would not necessarily be a good thing.  If the intent of a group is to communicate, breaking the organization into too-small groups would unnecessarily complicate the passage of traffic.  Conversely, too-large a group can make the proper prioritization and the management of the sheer bulk of traffic difficult:  Given the two choices, however, the latter case is arguably easier for skilled operators to manage, as it is always easier to deal with what you do know when dealing with the large group than with what you do not know if you are trying to deal with many smaller, fragmented groups!

One welcome challenge often faced by organizers of such groups is there are often individual, energized members, each being willing to contribute to the betterment of the group as a whole.  One aspect of this challenge includes the absolute need to make sure that these eager, members do not unnecessarily duplicate efforts - particularly when those efforts may, when the "big picture" is considered, actually decrease the overall effectiveness of the group as a whole.

One request often made of the frequency coordinator is that by a zealous individual that wishes to have additional frequencies for their local emergency services group.  While this may sound like a reasonable request, the coordinator must make sure that such a request is, in fact, one that receives the blessings of the organizers of the group as a whole and not an isolated effort by a well-meaning enthusiastic member:  You can surely imagine the chaos that would ensue if each individual took it upon his/herself to try to obtain the limited spectrum resource without appropriate regard to the needs of the organization at large!  Without careful management of the spectrum, large groups can become unintentionally fractured with much duplicated effort resulting in an overall decrease of communications effectiveness and efficiency.  This is not to mention very real and practical concerns about unintentional interference between the many groups that might result if their efforts are not appropriately coordinated!

To avoid such unnecessary duplication of effort and inefficient fragmentation, organized groups do not permit individuals to undertake their own, isolated efforts in such important matters as frequency coordination and the like.  While not always well-publicized, many of these groups have stated policies about such efforts, directing their members to work within the system (and not individually) to maximize both communications efficacy and organizational efficiency.

For an example of one such directive, see the document:  "Emergency Response Communications (ERC) Simplex Frequency Policy for the Wasatch Front.While this document specifically applies to the ERC group in particular, its stated goals and intentions are generally applicable to any group that has the need for amateur radio spectrum use to facilitate their communications.  Taking the ERC group as an example, individual members should not undertake frequency assignments on their own, but rather work with the group to assure the maximum effect of their individual contributions!
"I noticed that my newer radio has FM-Narrow on it.  What about using that to get more frequencies?
If you have a radio of fairly recent vintage, you may have noticed that it has an "FM Narrow" (FM-N) mode.  Also, you may be aware that digital voice modes such as D-Star take up less bandwidth than conventional FM signals.

The "conventional" FM that has been used for decades uses +/- 5 kHz deviation and has receivers that are a bit over 15 kHz wide.  As it turns out, for FM the occupied bandwidth is approximately the sum of twice the deviation plus twice the highest modulated frequency - a formula called "Carson's Rule", so for standard FM voice, that comes out to:

( (5 kHz) * 2 ) + ( (3 kHz) * 2 ) = 16 kHz

Where 5 kHz is the deviation and 3 kHz is the highest audio frequency.

And to make the receivers work properly, its own filters must be pretty close to that 16 kHz figure calculated above.  In Utah, our standard channel spacing is 20 kHz which means that we can comfortably put two channels that far apart and not have them bother each other.  In some parts of the country, 15 kHz channel spacing is used and it turns out that this is too close to avoid interference which is why special considerations are made when coordinating two repeaters that might be spaced that far apart - usually, they put two such repeaters as far apart from each other as possible.  (Note:  Since most people in Utah live along the Wasatch Front, we would have fewer available channels if we had both spaced them at 15 kHz and had to keep them geographically separated!)

Narrowband FM uses +/- 2.5 kHz deviation instead of +/- 5 kHz deviation, so if we run it through that same equation:

( (2.5 kHz) * 2 ) + ( (3 kHz) * 2 ) = 11 kHz

Where 2.5 kHz is the deviation and 3 kHz is the highest audio frequency.

At this point, you may have noticed something:  Even if we turned our deviation down to zero (something that is impossible to do and still get voice through it) the equation shows that we'd still occupy at least 6 kHz.  If you turn the transmitter's deviation down - which is the equivalent of quieter audio - you have to turn up the audio on the receiver to compensate, but if you have ever used FM you know that there's always a little bit of background "hiss" - particularly on weak signals.  What this means is that you will hit the point of diminishing returns when the hiss so loud on all but the best signals as to be distracting!

It's worth noting that if you transmit/receive narrowband on a wideband channel, others will likely complain about your low audio and your receiver may experience "squelch clamping" (e.g. the squelch closing on audio peaks - very annoying!) - but you will likely be able to communicate.

One problem with narrowband operation is the receiver.  As noted above, you need to have the receiver's filtering to be slightly wider than the signal itself because of several; factors:
  • If the filter is much narrower than the signal, the audio from signals passing through it will be distorted.  Taken to an extreme, this can be tiring to listen to as well as cause squelch clamping.
  • The receiver's filters aren't "brick wall".  You can have a filter that is 10 kHz wide to let the signal in without causing much distortion, but you can't have practical and inexpensive filters that will roll off extremely fast beyond this where the adjacent channel's signal will be.  What this means is that such a typical filter may not have useful attenuation until you get past 12-13 kHz bandwidth.
  • Frequency instability of radios.  It is possible for the transmitter to which you are listening (the repeater or another user) to be off-frequency, but it is also possible for your receiver's frequency to be slightly off as well.  Good amateur practice of new gear dictates that the accuracy should be around 2 parts per million or better which amounts to +/-0.3 kHz on 2 meters and +/-1 kHz on 70cm.  What this means is that it is possible for the combination of, say, a repeater's transmitter and user's receiver to be 2 kHz apart from each other on 70cm and still be operating within specifications!  If your filter was too narrow, that 2 kHz error would cause some very obvious and unpleasant distortion!  It's also no secret that older radios - or simply variations in manufacturing - can cause a radio to be farther off-frequency than its specifications!

So, knowing the above, how narrow can you go when using narrowband FM and get away with it?  The answer is a bit tricky, but you cannot put two narrow FM signals closer than about 12.5 kHz and expect to avoid undesirable interaction (e.g. interference) between the two.  Even at 12.5 kHz spacing, there have been reported some instance of undesirable interference between two channels, but apparently not as bad as one would experience with "normal" (+/- 5 kHz deviation) FM at 15 kHz.

What this means - in theory - is that you could put narrowband channels 12.5 kHz apart and get away with it in many situations!

There are some complications that make this harder to do than you might think:

  • In the U.S., 2 meter channels are spaced either 15 or 20 kHz apart - and 12.5 kHz spacing really doesn't fit into any of these plans!  In order to make 12.5 kHz spacing to work and save spectrum you must put several 12.5 kHz channels together and hopefully, you can arrange so that one (or both) of the "ends" of these channels will waste as little spectrum as possible when you abut "normal" FM operations.  (You must have at least 15 kHz between a "normal" FM channel and a "narrow" one - yet another complication!)  In those area with very heavy channel usage, getting everyone to play along and reshuffle their channels can both very difficult and it could be quite expensive.
    • On 70cm - with its 25 kHz channel spacing - it is possible to divide one channel into two narrowband channels, but this requires that everyone using those "new" channels have narrowband radios that can tune in 6.25 kHz steps.  Fortunately, most radios that also have FM-Narrow capability can tune in 6.25 kHz steps.
  • EVERYONE using a narrowband channel MUST remember to switch their radio to narrowband FM mode when transmitting on OR listening to a narrowband channel.
    • If you listen to a narrowband channel on a "normal" FM receiver (e.g. no narrowband) you will get interference when there is a signal on either of the adjacent channels.
    • If you transmit on a narrowband channel using a "normal" FM transmitter you will cause interference to the two adjacent channels AND your audio will likely sound loud and distorted to those who are listening to you on narrowband receivers.

Unlike with digital modes, there's a bit of compatibility between wide and narrow FM rigs so it would be very easy to accidentally to transmit on a narrowband channel using a transmitter set to wideband mode with a user causing havoc to THREE channels!  This usually doesn't happen between "normal" FM and digital modes since the radio will automatically set the bandwidth on the mode!

As mentioned above, digital modes can take up less bandwidth - and there isn't the "operating wideband on narrowband" channels problem - but the same issues about channel spacing and frequency stability still apply:  You about have to clear a block of adjacent narrowband channels (analog or digital!) in order to save much spectrum at all!

"If someone gets on my repeater and does illegal things, whose responsibility is that?" This isn't a particularly easy question to answer as each situation is unique, sometimes resulting in a slightly different interpretation of the rules.  There are a few things to keep in mind: 
  • Any automatically-controlled repeater must have a means of control.  Often, this is done using DTMF on the input frequency.  The control operator may use these tones to turn the repeater's transmitter on and off in addition to other functions.  If the repeater is located at a residence, for example, then simply being able to power-down the repeater will usually suffice.  Note:  Until 12/2006, such control on frequencies below 222 MHz was not permitted - it is now legal on certain portions of bands from 2 meters and up.
  • It is expected that the repeater licensee (or a designated trustee or control operator[s]) keep track of what is going on on the repeater(s) in their charge.  While it is not expected that the repeater be monitored 24 hours a day, it is expected that the operator(s) can be contacted should questionable operations occur on the repeater.  If these operations are contrary to the rules, it is then expected that action be taken to prevent such operations in the future.
Recent FCC actions in cases of on-the-air misconduct have generally gone as follows: 
  • The offending operator has been identified by those in charge of the repeater in question, contacted, and informed of the problems.  Sometimes, the offender is unaware that he/she is causing a problem or, after anonymity is lost, simply ceases such operations.  The problem often ends there.
  • If the offending operator continues to flaunt rules, it is the responsibility of those in charge of the repeater to do several things:
    • Document the offenses.  Make recordings (with time/date stamping) of the occurrences.
    • Document the efforts made to identify the offender.  Was there a foxhunt to find the offending operator?  How did you figure out who it is/was doing this?
    • Document contacts made with the offender and his/her responses to these contacts - or lack of them.
    • Document action taken to prevent such operations.  This might include turning off the repeater, adding/changing subaudible tone frequencies, 
  • If none of these efforts help curb those inappropriate operations, it might be time to contact the FCC.  Keep in mind that the FCC can do nothing unless there is documented evidence pointing to the offender.  Written reports of actions taken - as well as other material evidence (such as recordings and affidavits) are required to provide evidence of guilt.  The FCC can (and will) do nothing without a body of good evidence to substantiate charges!
As unfair as it might be, even if the operator continues to operate even after he/she has been contacted and/or after the FCC has been contacted - or even if the FCC has carried out enforcement action - the FCC has made it clear that it may still be required for the repeater operator(s) to shut down a repeater to prevent illegal operation on that repeater.

Do you have any questions/comments for the frequency coordinator?  If so, send an email.

For more information, you might want to read the  "So you want to put up a repeater?" page.

Return to the  Utah VHF Society home page.

Updated  1 March, 2016

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