• "Why Frequency Coordination?"
• "My repeater's off-air.  What do I do?"
• "Why are Utah's 70cm repeaters' splits backwards?"
• "I already own a repeater - Gimme a frequency!"
• "Whose hoarding all of these frequencies?"
• "Why aren't some frequencies used?"
• "Who are you to say which simplex frequencies I can't use?"
• "I have a portable/mobile repeater - Gimme a frequency!"
• "Where can I operate my 'simplex' repeater?"
• "Why can't I just operate wherever I choose?"
• "Why have a subaudible tone on a repeater?"
• "How does one go about getting a repeater on the air?"
• "Why doesn't everyone operate using D-Star?"
• "What about Yaesu's VHF/UHF digital voice system?"
  
• "D-Star and Analog can co-exist on the same channels, right?"
• "D-Star's narrow signals can allow a lot more repeaters, right?"
• "How are repeater frequencies 'shared?'"
• "If someone does illegal things on a repeater, who's responsibility is that?"
• "How about this narrowband stuff?"
  

• "How does one become frequency coordinator?"
• "What are bandplans?"
• "I want a repeater - Gimme a frequency!"
• "I don't hear anything on this frequency - I want to put my repeater there!"
• "We could have more repeaters if we had a 15kHz spacing, right?"
• "What are these 'SNP' repeater channels?"
• "What's with 'coordinated' simplex frequencies?"
• "Where can I operate my 'crossband' repeater?"
• "Where can I operate my simplex Echolink/IRLP/whatever node?"
  
• "Why can't we re-use frequencies like they do with cell phones?"
• "Why are there 'closed' repeaters/autopatches?"
• "Why not allow subaudible tones on simplex?"
• "Why not 'invert' a few repeaters to fit a few more in?"
• "D-Star's range and audio quality range is better because it's digital, right?"
• "Yaesu's C4FM is also narrow so we can cram more of those in than analog, right?"
  
• "Can you 'DF' (direction-find) D-Star/C4FM/Digital audio signals?"
• "Once a frequency is coordinated, it's mine, right?"
• "I need frequencies for my emergency services group - give me some!"
  

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. 

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.

• What parts of your system are off the air.
• When it happened.
• What happened.
• When you expect to have it back on the air.

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.

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

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.

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.

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!

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.

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...)

• 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.

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.

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.)

• 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.

• 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.

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

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 here.  It 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.

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.

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! 

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. 

• 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"!

• You must work through the Frequency Coordinator who will also put you in touch with the Simplex Frequency Manager to determine an appropriate frequency, knowing that it probably will NOT be on the 2 meter band!

• 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!

• 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.

• 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.

• 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.
  

- 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 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.

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.

• 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.

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.)

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.

• 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.

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.

• For an audio clip providing a comparison of normal analog and D-Star, click here.  This 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.
  

• 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.
  

• 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.
  

• Observations of the codec used for D-Star - How does the codec used for D-Star respond if subjected to sounds other than those of the human voice?  We decided to find out.

• Digital Project Working Group Interim Report, May 2008 - A report by the International Association of Fire Chiefs about studies of analog and digital voice systems.
• Phoenix Fire Department Radio System Safety report - This report contains detailed analysis by the City of Phoenix pertaining to real-world use of both analog and digital radio systems, linked from this page.

• 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.

• D-Star to D-Star channel spacing:  12.5 kHz minimum
• D-Star to Analog channel spacing:  15 kHz minimum

• 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.

• 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.

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.

• 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.

• 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!  It is for this reason that on 2 meters in parts of Utah, the lowest repeater channels (those just above 145.100) have 12.5 kHz spacing.

What about digital modes like Fusion, D-Star and DMR?

First off, Fusion uses the same bandwidth as analog signals, so this cannot be "narrow-banded" in the same way that analog signals might.

D-Star and DMR both use narrower deviation and narrower receiver bandwith - but they are both FM, with a digital signal substituted for voice and as such, they are also subject to Carson's Rule, above.  While most of the energy of a modulated D-Star/DMR signal is contained within 10 kHz or so of bandwidth, it is still required that the receiver's filters be wider than this to accommodate real-world effects like limited filter-skirt steepness and frequency inaccuracies of the repeater and the user's radio, to name but two.

Originally, it was suggested by proponents of D-Star (and, to a lesser extent, by DMR) that these would work with 10 kHz channel spacing - and, in a few areas of the U.S., this was done - but with disastrous results:  One could not have a "nearby" (within a few miles) and a "distant" (within a few 10s of miles) repeater on adjacent frequencies without the nearby one clobbering the distant one.  In Utah - and many other places - a 12.5 kHz channel spacing was established as a bit of a compromise:  Less "strong-versus-near" degradation and also the simple fact that in many situations, users of digital radios would either not notice the degradation due to the "digital cliff" (that is, the signal sound just fine - until it doesn't) and they wouldn't know what they were experiencing - or what to do about it - anyway.

• 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.

• 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!