|What is a Voter?
An overview of receiver voting systems
By Mike Morris WA6ILQ
A “normal” repeater system has a receiver and a transmitter, connected by some form of repeater controller, and located at an optimal site for reception and transmission. The system coverage is usually dependent on the geography of the surrounding terrain.
Early public safety dispatch systems had a problem – they had high power transmitters and good receivers and antennas, but the lower-power mobile units (i.e. patrol cars) would be able to hear the dispatch transmitter, but not be heard by the dispatch receiver.
Early voting systems used multiple audio tones to indicate receiver carrier signal strength, but these were superceded by ones that worked by measuring the signal-to-noise ratio on the fly. Due to the fact that a full quieting signal sounds like a squelched (muted) receiver, an idle channel (i.e. one that was squelched) was indicated by sending a constant precise frequency audio tone down the wire-line – this was, obviously, called the idle tone, or the idle marker. GE used 1950 Hz, Motorola systems used 2175 Hz just to be different. The status tone identified to the voting panel that the wireline between the receive site and the voter input was intact, its presence or absence told the voter that the receiver had squelched or unsquelched, and was used as a reference for setting audio levels.
One “gotcha” was when the voting unit was located at the same site as the dispatch base station – most voters are designed for voting wire-line-connected receivers and the base station receiver wasn’t. Some installations wire-lined the base station to the dispatch center and put the voter there, others left the voter at the base station site and used a special interface card to allow a local receiver to talk to the voter channel assigned to it.
- Receiver voter / receiver voting selector / voting panel / voter: The equipment, usually rack mounted, that interprets the audio from several outlying receivers (usually connected by leased phone lines) and picks the best quieting signal on the fly and routes it to a single output. Voting is continuous and the switching can be as fast as 10 times per second. Control options allow forced selecting a specific receiver, and to disable specific receivers (sometimes referred to as “failing a receiver” or “force failing a receiver”). The leased lines weren’t cheap – the in band signaling used upper audio frequencies above 2700 Hz. The lines were equalized to be flat from 300-3400 Hz.
- Channel: The number of receivers that a single voter unit (called a shelf) can handle is usually enumerated as a channel count. Voter shelves come in 2, 4, 6 or 8 channels (depending on the manufacturer), and some manufacturers have kits that allow multiple units to be tied together. For example, GE has a kit available that ties two 6-channel shelves together into a single 12-channel voter.
- Voting receiver / remote receiver / satellite receiver: an outlying receiver that feeds the voting panel. The term is sometimes used to refer to all of the equipment at the outlying site – the antenna, receiver, controller, link transmitter, etc.
- E & M: a generic term used to describe a type of telephone trunk (inter-office) circuit (wire line or microwave)… The letters “E” and “M” are labels for a status signal, or a “busy” lead that was transmitted down the path along with the voice. The “M” lead (for “Mouth”) was made active at one end and on the other end a relay pulled in and provided an active signal out on the “E” lead (for “Ear”). Think of the “M lead” as being the PTT on one end of the leased line circuit and the “E” lead as the COR on the other end. Depending on the type of equipment used, the E&M circuit can be implemented over connections that have DC continuity between the two ends, or connections that require using tones to indicate status (which are filtered out at the receiving end). Some types of E&M circuits (mostly on microwave systems) allow multiple status signals in each direction (one could be, for example, COR and a second could be PL decode). E&M circuits consist of the balanced audio pair plus the status signals, which can be -48vDC referenced. E&M circuits can be one-way, or bi-directional. Overall, E&M technology is much more complex than this, but the above is enough for this write-up.
Basically from the point of view of the repeater controller, the output side of the voting panel chassis is the local repeater receiver. Once the voting panel is properly connected and set up the repeater controller sees what it expects: receiver audio, COR and PL tone decode (if a non-carrier-squelch system). Each input channel of the voter is connected, either by wire links, E & M links (wire line or microwave) or by point-to-point analog RF links (usually on 420-430, 900 or 1200 MHz) to a satellite receiver. When any (or several) of the receivers un-squelch the voter does an on-the-fly comparison of the signal-to-noise ratio of each of the incoming signals and feeds the best one to the repeater transmitter. It is not unusual in a properly configured voting system to have a multi-syllable word “assembled” from multiple sites. A good voting system is completely transparent when it’s working properly – you can’t tell it’s there. Obviously the voter has to be voting identical signals, which is why using VOIP (voice over IP, a.k.a. the Internet) as a link to bring in the audio from one or more outlying receive sites does not work – there is too much delay and manually adding a fixed delay to the local receiver(s) does not work either, as the internet delay is not consistent, even within one transmission, and definitely not from one transmission to the next.
The signal to noise comparison in the signal-to-noise voters is made by looking at the channel noise at the times that speech energy is not there (note that some cheaper voters simply rectify the high frequency noise and that technique does not work as well as a true signal to noise system). You can’t count on the high frequency squelch noise above 4khz since it’s not carried by some link facilities – microwave or point-to-point RF links. On this web site there is a relevant technical article on the LDG Corp RVS-8 Voter. Read it more for the technical overview than for the sales pitch.
The Motorola and GE manuals on their voter systems have a theory section in the front, ahead of the schematics. The manuals on the two vintages of GE voters is available on the LBI master index page at this web site. Look for LBI-30002 for the older, grey-painted unit (all discrete components) and LBI-38676 for the newer black painted unit (with a mix of discretes and ICs). It’s worth grabbing either one for the theory part. You will want to grab LBI-31981 for the idle marker encoder (i.e. at the outlying receive site). The GE voting panels operate on 120v/240vAC, or 24/28v DC. If you will be powering it from 12v you need LBI-4583.
1)Improved Portable Coverage: This is the big selling point in the public safety marketplace. With a multiple-receiver system you can have a coverage situation where a handheld can provide communications quality that would normally require a 60w mobile (or higher), and if you have cops on foot on a beat that’s really important. You can add receivers wherever there are gaps in the system receive coverage, and as many as you have voting panel ports… and if need be you can cascade voting panels: the Los Angeles County Sheriff’s old conventional (i.e. pre-trunked) 39 MHz dispatch system used a 12-channel voter (two GE 6-channel chassis tied together with the option kit) with each voter channel fed by the output of another 12-channel voter. And this configuration was duplicated for each dispatch radio channel! I once counted over 60 six-channel voter chassis in one room of open frame 19″ equipment racks, and had to stop when the tour moved on – there was at least a third more to count, and knowing how many radio channels and receive sites the Sheriff had then, I suspect that there was at least one more room of voting panels…
2)Redundancy: You can lose one receiver site and the system isn’t completely dead. Yes, you will have a receive coverage hole (assuming non-overlapping receivers) but the rest still works, and those users that can reach another receive site (i.e. those with real mobile radios as opposed to handhelds) may not even notice the coverage hole. You can also place standby (backup) transmitters at any of the receiver sites if you want (all it takes is money for the backhaul link, the transmitters and the duplexers…). Simulcast systems – those that use more than one system transmitter is transmitting the same audio signal on the same (repeater output) frequency simultaneously is another can of worms best dealt with in another article.
1)Expense: rent on the outlying receiver sites – both building rent and additional antenna space (many sites include one antenna location with the rack space rental and charge extra on a per-antenna basis). The voting receiver site needs a omni antenna for the system input receiver (with one exception covered later) and a beam for the link transmitter that talks back to the central voter site. Sometimes you can get a feed from someone else’s omni receiver antenna. If you plan on ever adding a voter to your system (at any point in the future) you might want to juggle the wording of your site rental agreements as far in advance as you can to allow you to add additional antennas later on without an increase in rent. Or you can do as we did at one site: we mounted a 3-foot (1 meter) piece of thick-wall galvanized steel pipe on the tower where the single antenna would have gone, and mounted a stationmaster onto the top of the pipe and at the bottom of the pipe we side-mounted an end-mount 4-element 420 MHz beam.
The exception mentioned above is where the voter receiver site is located near the periphery of the transmitter coverage with a 120 degree (or 180 degree) coverage antenna pointed inwards. The directional coverage can be configured easily by side mounting an omni antenna a carefully selected distance from the tower.
2)Multiple sets of duplicate equipment required: In order for the system to be “audio transparent” every voting receiver site needs to have the exact same audio characteristics – and for two reasons: one, the voter does it’s voting totally on audio characteristics and quality – if the sites sound different that will negatively affect the voting process. Second is that it affects clarity and intelligibility – if the voter were to select a different receiver in the middle of a word, or even change receivers multiple times in the middle of a multi-syllable word (it does happen more often that you’d expect) and the audio from the first receiver was normal, the second receiver was bassy and the third receiver was tinny it would be very hard, if not impossible, to understand. The simplest way to guarantee consistent audio quality is to have identical equipment at each site. Having identical equipment also makes for simplified repair – just swap a dead chassis with a good spare. Or swap a complete cabinet. If you plan on adding a voter to your system in the future you may want to start to keep your eyes open for multiple identical sets of 420, 900 or 1200 MHz continuous duty equipment with direct FM exciters (no phase modulators) for the links and a number of identical main input channel receivers. Yes, there is a use for 406-420 MHz or 900 MHz radios!
3)Expense: Point-to-point links… each satellite receiver needs a audio and COR link back to the voter, and that means multiple sets of link hardware needs to be acquired – be they wire-line, microwave, 420 MHz, 900 MHz, 1200 MHz or whatever. And the linking methods can be mixed as long as the audio characteristics are matched (which can be harder than it sounds). One local amateur system here in Los Angeles goes all three routes on it’s voting receivers: two sites talk back to the voter via E&M channels on a private microwave system. Another receiver is in another building at the same mountaintop site (think “diversity reception”) and linked in by 200 feet (about 70 meters) of wire (they found an abandoned antenna on the tower so they installed a receiver and ran their own DC wire-line between the two buildings). Several additional sites are brought in via one-way 420 MHz or 900 MHz point-to-point links. Plus there is the original in-cabinet repeater receiver for a total of six. If you were to listen very carefully you could tell which type of site is the last site voted – you’d hear a) the normal squelch crash then almost immediately a very, very short chirp when the microwave link squelched, or b) the normal squelch crash then a little bit of a second squelch tail when the 420 MHz RF link squelches or c) the normal squelch crash then absolutely nothing when the main site – either the in-cabinet receiver or the DC wire-line (diversity) receiver squelches. And if the user is using a radio with reverse burst, the first squelch crash is completely missing. Note that the links that carry the received signal back to the voting panel have to be noise free – if RF based they have to be full quieting ALL THE TIME, even during rainstorms or snowstorms (which can affect a 1200 MHz link pretty bad… and 900 MHz to a lesser extent. The water in the air absorbs RF much more readily than at 420 MHz). Any link noise will confuse the voting process. You could have a perfectly quieting signal at a satellite receiver, but if the link path is noisy the voter will do just what it is supposed to do and vote the best quieting signal it sees at that moment. The satellite receive site, if using a RF link, can be almost as complex as the main repeater – it is, after all, a complete cross-band repeater, in some cases with both main channel and control receivers. And a constant 20db quieting on the RF link is a good start, usually you end up needing quite a bit better.
You can cheat a little on the equipment at the main site (the receive end of the links): The link receiver antenna is usually an omni followed by a preamp / multi-coupler feeding multiple receivers. If you have a good antenna with a band-pass “window filter” like those made by DCI and others the link receivers can be mobiles: I have seen stacks of Micors, Mitreks, MaxTracs, Radiuses and even 1970s vintage Motrac / Motran receivers used as 420 and 900 MHz link receivers. One system uses a Down East Microwave block converter that “translates” a set of 1200 MHz link channels down to the 150 MHz range feeding a stack of 1980s vintage high band E.F. Johnson mobiles as link receivers…. Another system uses the receive chassis from an old UHF-to-HF transverter to convert a block of the 438-439 MHz range to a number of (otherwise pretty useless) 36-42MHz band Motrac / Motran receivers (they had salvaged the receiver chassis and the control heads and junked the rest). They made it easy on themselves: to make the conversion just subtract 400 MHz… 439.925=39.925, 439.950=39.950, 439.975=39.975, etc. Equipment for the middle range of low band can usually be had for low prices or sometimes even for the taking: 30-36 MHz gear ends up on 10m, and 42-50 MHz gear ends up on 6m. Absolutely nobody (except volunteer fire departments) wants the 36-42 MHz stuff in between, and they want recent stuff.
4)Complexity: The overall system design must preclude some failure modes from taking down the entire system. A failed link receiver (i.e. no audio) appears as a full quieting signal to the voter and can lock up the system unless you have an auto-disable timer on each receiver site. This is a built-in feature of the GE voting panel. The more complex the overall system the more you have to think ahead of Murphy’s Law. And Murphy was an optimist. Example: One group built their own repeater controller. They installed it on a hill and a year or so later the -12vDC supply died, which via a design quirk caused the repeater transmitter and all three point-to-point link transmitters to simultaneously key up – continuously. And the failure happened during the worst rainstorm in over 10 years. They had to hike in to the repeater site, over 12 miles on dirt roads (read: mud deep enough to suck your boots off) in sheeting cold rain and snow. By the time the transmitters were shut off it was about 30-36 hours later. Moral of the story: don’t forget to consider (and test) all the failure modes. And have two ways to shut off the transmitters.
5)Expense and Complexity: A voter-based repeater has additional complexity and expense that increments with each satellite site that is added: for example, every site needs an omni antenna for the main channel receiver, maybe a pass cavity, a main channel receiver, a continuous duty link transmitter and a controller to control the various functions of the outlying site. The RF- linked sites in system mentioned in #3 above have a remote “package” consisting of a system input receiver (on 443 MHz), a link transmitter (on a 420-430 MHz frequency) and a system output receiver (on 448 MHz). Some folks will tell you to just strap the local input receivers COR to the link PTT and let it go, but there are several good reasons to use a low-end controller on your cross-band links: timeout, ID, remote control, and telemetry. Each outlying receiver site is by definition a cross-band repeater that has to follow FCC rules as well as good engineering practice guidelines. The local controller in the above mentioned system is a very simple PIC processor based board that couples the VHF receiver to the link transmitter, and has a touchtone decoder that listens to the 448 MHz receiver (or you could use a commercial low-end controller). The groups PIC controller is built on a plug-in card, for easy replacement, and the site number is set by a DIP switch. This allows the control sequences for the remote sites to be set up so the sequences do not overlap – the site number is part of each control sequence, and the site number is included in the link ID (i.e. w6xxx/n where the “n” is the site number). The local controller listens to the system output (448 MHz, in this case) so that if you can’t be heard by the site you are trying to control you can still control it as long as you can get into any receiver of the system. Picture a situation where you need to shut down the north voting site and you can only be heard by the south site. The main controller has a command that un-mutes the system output and then the commanding of the outlying sites is done via that method, for example the command might be “2*456#” where the unmute command could be “2*” (which also inhibits any local command interpretation until unkey), the site number is “4”, and the shutdown command is “56#”. The site controller is very simple: it has site on/off commands (in reality two commands – one for transmitter PTT enable and the other for transmitter DC power on / off via a relay as a backup shutdown method), audio selection commands (transmitter keyed with (1)main channel receiver audio, (2)no audio (for testing link quieting), or selectable test tones at several frequencies and each can be sent at different levels… 300Hz, 600Hz, 1khz, 3KHz, 4Khz, and at 1Khz dev, 3Khz dev and 4Khz dev.). The whole voting receiver assembly was implemented by taking a GE Mastr-II “E” case (the double-high case) UHF 420 MHz radio and replacing the UHF 420 MHz receiver with a 443 MHz receiver and adding a 448MHz receiver into the second tier. The leftover space inside was occupied by the controller hardware and an old flat-pack UHF duplexer used to notch the 420 MHz transmitter out of the two UHF receivers (the duplexer was used as two separate notch assemblies, with the antenna feeding the center point and the two duplexer ports feeding the two receivers). It’s a nice package: one radio chassis, one Astron power supply, a short UHF Stationmaster mounted about 8 feet above an end-mounted 6 element 420 MHz beam, both mounted on a 30 foot pushup mast (most of the receiver sites involved with this system are at low profile / low RF level residential sites – a notch-only UHF mobile duplexer is enough).
6) Complexity: The main system controller (the one at the site where the voting panel is located) needs additional digital outputs to force fail (i.e. disable) specific receivers, and some kind of interlock logic so that a brain-faded control operator does not disable ALL of them at the same time (sometime ask me how I remembered to mention that….) locking everyone out completely until someone goes out to the site. Very few controllers have enough digital outputs to be able to dedicate six (or eight or even twelve) to that purpose, and fewer have enough smarts in their “programming language” to prevent all of the disable functions from being turned on at the same time. And yes, you will need to do that… for example, I know of one voting system in the Midwest that disables their northeast receiver during summertime band openings as users from the nearby same channel system are heard by the receiver just enough to key it up but to not be understandable. For 9 to 10 months of the year those users are not a concern, just during troposphere ducting periods.
Another feature that few controllers have is enough digital inputs to be able to sense which receiver is selected (again, anywhere from 6 to 12 depending on the manufacturer of the voting panel) plus a way to “totalize” the amount of time the system spends on each receiver. If yours can, then it’s worth doing the programming for that as the statistical data that is gathered helps the system tech committee determine which receiver is used the most, and helps spot failure trends… if, for example, all of a sudden the prime receiver is voted 50% less it may be time for a site visit to check the receiver sensitivity.
7) Complexity: Carrier Squelch systems are simpler than PL systems, but tone access systems are more the norm these days…
- How do you switch the entire system from carrier to PL and back, or do you run a single-mode system? (Remember, if you have three remote receivers plus the main receiver that’s four sites where you need to change the mode).
For what it’s worth, most amateur voting systems that I am aware of run the main channel receivers and the links as carrier squelch (with a very long timeout) and set up the link path to carry 60 Hz to 4.5 KHz flat… (not hard if you run main channel receiver discriminator audio right into the a link transmitter direct FM modulator with no audio processing other than a brick wall amplitude limiter at 4.5khz of link transmitter deviation). At the main site they put the user PL tone decoder behind the voting panel, then pipe the output of the voting panel into the main channel receiver port of the repeater controller.
- If you run PL, do you run one common PL tone, or do you run a common tone ORed with a unique tone per site so you can test coverage and do a quickie system debug? (hint: if you don’t do the latter, you will wish you had) If you run everything in front of the repeater controller as carrier squelch this is easy.
- Where do you put the PL decoder that decodes the user’s PL tone? Do you put a PL decoder at each voting receiver site, or do you put it at the central voter site? If you chose to decode at the outlying site and regenerate the user’s PL before it goes over the links you add another decoder pickup delay to the mix… not good. (Hint: multiple cascaded PL decoders cause unacceptable pickup delays – figure a worst-case scenario of 1/3 to 2/3 of a second per decoder – do you really want your users to have to squeeze the PTT and wait a full second to a second and a half before they can talk? Unless you are desperate never put more than one PL decoder between the user and the system transmitter.)
If you chose to put the PL decoder(s) at the main site, you have to make sure that the entire path from the antenna jack of the remote receiver through the local controller then through the link transmitter then through the link receiver can pass the user’s PL tone itself without any measurable distortion! Hint: a distorted PL tone results in slow PL decode action (if it decodes at all).
- Do you filter the PL out before or after the voting panel? Some link receiver designs provide a PL-filtered repeat audio output, which makes the connection to the voter simple, some don’t. Some voter designs are affected by the presence of a PL tone – this is easy to test / measure… You may have to put a high pass audio filter and the PL decoder in front of each voter port rather than one after the voter… You will find that the level of the PL encoder in the user’s radios is not consistent from radio to radio, and many of the newer ham radios have excessive PL deviation right out of the box…
If the voting process of the voter is not affected by the PL tone and the voter does not distort the PL tone then you can put the user tone PL decoder on the output of the voting panel and use the PL decoder in the link receiver (if you have one) for the unique / test tone. Run the link receiver in carrier mode, and wire it’s PL decoder to the “force vote” input of that voter chassis port and “OR” it to the repeater controller PL decode input. Just make sure that the phase of the audio from receiver to receiver into the voting panel is consistent. If one is wired 180 degrees out of phase, then when the voting panel switches from the in-phase receiver to the out of phase receiver the tone decoder would see the phase suddenly invert which would quench the CTCSS decoder… in other words it would look like a reverse-burst and slam the squelch closed.
One trick on link PL tones… if you absolutely have to use a link PL then consider notched audible or “supersonic” PL… the decode time is much much faster on audible tones than sub-audible tones…
Notched audible: The regular Motorola wire-line AC remote control tone panel uses 2175hz as a PTT marker tone (tone on during PTT). You could use that same frequency as a “PL” tone, with a notch filter at the voting panel input – it would have to be at the input because the tone would confuse the voting function. This same idea is used by AC wire line or microwave E & M systems – the M lead switches an audio tone that is decoded at the far end as the E lead, and the tone is notched out of the link receiver by a deep narrow notch and never heard by the end users. That tone notch technique is also used to ID the links in multi-hop linked systems – one common ID frequency is 1064Hz, right in the logarithmic center of the gap between low group and high group touchtone… (the ID tone thus has a minimal effect on any downstream touchtone decoders)
Supersonic PL: In normal usage the term supersonic refers to a sound frequency above the range of human hearing – 30KHz to 35KHz for example. In 2-way usage this term refers to above-the-audible, but in this case that’s limited to 4 to 5khz. If you look at the audio performance of the average FM receiver you will see that audio frequencies above a certain cutoff point are treated as squelch noise. You want to pick a frequency just a hair below that point (so there is no attenuation of it) and use it as a PTT indicator, and then notch it out before the voter – you have to do that since the supersonic tone will be right smack in the middle of the squelch noise range that the voter is trying to use to vote with… and you want a narrow enough notch that the voter still gets enough noise to work properly.
8) Complexity: Fine Tuning of the system: The audio levels at the voting panel between receivers are very critical as are the levels between the audio and the status tone (if used). Everything needs to be exactly the same for the comparator to properly vote the best receiver signal. Make sure the audio response of all receiver paths are adjusted the same, using all the same remote receivers is the easiest way.
In closing, realize this: Taking a regular single-site system and adding a voting panel and maybe two outlying receivers has just raised the hardware complexity (and maintenance requirements) from the original one repeater to more than three separate repeaters. Each outlying receiver site is a repeater (usually cross-band) by itself (unless you luck out and have access to in-place microwave E&M links), and the main site is now an extra-complex multi-port repeater (local main channel receiver plus all the link receivers plus the voting panel). It may take a month of weekends (or even more) to rebuild the original repeater to place the voting chassis in line, get the first link receiver working, then sorting out all the adjustments… and simultaneously the other team of guys is getting the first outlying receiver site operational and talking back to the main site. Then you get to do a major chunk of that work over and over again for each new voting receiver site. Can your repeater committee handle that workload? Do you have the technical competence in your group to keep such a system running if the key person suffers repeater project burnout? or has a heart attack?
One suggestion: Find somebody who has set up and runs a voting system (public safety, commercial or amateur) on a daily basis, buy him dinner and a few beers and get him talking. You will learn a lot – maybe more than you wanted to… You may even decide to not implement a voting system, and to improve the single site system you already have. It might be easier to add a pass cavity and a good preamp ahead of the main receiver, or to convince the users to use 30w to 50w mobiles (maybe even with dual band mobiles that repeat their dual band handhelds) into the improved existing system than to contribute to the implementation of a multi-site voting system so they can use flea-powered in-band handhelds.
One thing that hasn’t been covered here is the budget: You can pick up a 6-channel shelf of the older grey GE voting panel on eBay today (mid-2005) for under US$100 dollars and you can find auctions where the seller will pay the shipping costs. It takes the right manual, a logical brain, some good test equipment, some serious integration and adjustment time (and think carefully – what is your time worth?), and a few interface tricks. And the early grey ones are easier to fix for some folks – they used all discrete components where the later black ones used a mix of ICs and discretes. As mentioned above you can download the manuals on either one from this web site.
Motorola Spectra TAC voters go for similar prices on eBay, but manuals have to be purchased, and many are no longer available.
If you do go with a ground up new project, you have to toss around the choice of a true signal to noise voter (GE or Motorola) versus the rectified high frequency noise voters that tend to be more popular. Both work fine for many applications but the true signal to noise type work much better, especially over point-to-point radio or microwave links (and the interfacing effort is the same).
Remember that acquiring the voting panel is only the start – you need to acquire the point-to-point link for each outlying site, and being able to access someone elses spare E&M ports on any already-in-place microwave shots is HIGHLY unlikely. And you will find that the linking equipment costs a LOT more time and money than the voting shelf – and then there is the ongoing site rental and increased maintenance costs. And if you are going to deploy N satellite receivers you will need N+1 or N+2 sets of identical linking equipment (the +1 or +2 is for hot spares)…
Another coverage improvement method is to multicast using a hub repeater. Take N number of 2m (or 440MHz) repeaters, each with it’s own coverage area and user base, and add a 220MHz, 420Mhz, 900MHz or 1200MHz radio to each one that talks back to a central or hub repeater (i.e. a one-channel remote base on a beam antenna). The hub repeater has no “users” but the outlying 2m (or 440MHz) repeaters. Each individual 2m (or 440MHz) repeater has three modes in the remote base: local only, hub monitor and hub transceiver. In local mode the repeater operates normally. In “hub monitor” mode the remote base receiver is active and the local repeater monitors the hub repeater. In “hub transceiver” mode the remote base receiver is active as is the transmitter and all local traffic is fed to the hub repeater.
The users do need to keep track of which local repeaters coverage area they are in, and change channels in their radio to compensate for their travels. Some manufacturers, including Tait, make mobile radios designed for multicasting operation and when properly configured will vote the best frequency in the multicast group.
The N3KZ/R system is a good example of this technique – they have over a dozen UHF systems talking back to a hub system.
Note from the webmaster: This was copied from the repeater builder website. No infringement of copyright is expressed or implied. It was not my intent to infringe on the authors rights. I just wanted to provide the information here as well as on the repeater builder website. Please check out the repeater builder website for more information on anything to do with repeaters.