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I saw a couple YouTube videos last night about setting up a repeater using a pair of cheap hand-held radios and, at its simplest, an audio patch cable to connect the speaker output of one radio to the mic input on the other. Set frequencies correctly, turn VOX on, and what one HT receives will be retransmitted by the other -- potentially even cross-repeating between 2m and 70cm bands, or whatever bands your radios can use.

There are potential issues with doing this on a non-emergency basis -- protecting the radios from weather, keeping their batteries charged, preventing someone from finding the setup and saying "Hey, free radios!" The one I'm concerned with at the moment, however, is FCC legality. It's my understanding that periodic ID, at least when active, is legally required, but none of the other repeaters I've listened to seem to do this.

Since the cheap HT sets don't have this capability, I'm concerned about the legality of operating a repeater that doesn't identify itself. Just because another repeater doesn't (that I've heard), doesn't mean it's legal to do things that way.

Is there an inexpensive way to insert an ID generator between the receive and transmit HT units in this kind of setup? It would need to detect activity, wait some period of time, and then send an ID, as well as sending periodically if there's no activity. Either voice or Morse is legal, but presuming this will be a digital playback system of some kind, either one is easy to set up.

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    $\begingroup$ I've never encountered a repeater that didn't ID — but bear in mind it only has to ID when it's active. Not every 10 minutes, just every 10 minutes in which it's transmitting. And audio or morse ID is sufficient, both aren't needed. $\endgroup$
    – hobbs - KC2G
    Mar 28, 2019 at 15:33
  • $\begingroup$ Periodic morse ID and timeouts is a task for a cheap MCU, which is the way it's been being done for several decades now. An "Arduino" would work if you plan to DIY without previous familiarity. Ideally you make a little effort to produce somewhat sinusoidal audio. $\endgroup$
    – Chris Stratton
    Mar 28, 2019 at 16:15
  • $\begingroup$ Given I've seen video of Arduino used as frequency synth for HF WSPR transmitters, I expect it's got plenty of spare cycles to make at least an 8-step audio at 600 Hz. $\endgroup$
    – Zeiss Ikon
    Mar 28, 2019 at 17:41
  • $\begingroup$ The FT-8900R and TM-V71A are designed with built-in cross-band repeater functionality. The TM-V71A has a built-in 10-min CW ID function; the FT-8900R does not. Since both are popular radios, I infer that the regulations and/or enforcement are hazy / spotty. $\endgroup$
    – Brian K1LI
    Mar 29, 2019 at 12:30
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    $\begingroup$ @BrianK1LI Since the FCC is the final decider here, I'd be more comfortable with strict construction. If they decide you're wrong, the least that's likely to happen is loss of your ham license. $\endgroup$
    – Zeiss Ikon
    Mar 29, 2019 at 14:39

3 Answers 3

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Are you up to buying a Raspberry Pi, two USB sound cards, some assorted transistors and such, and making your own interface cable? If so, you can run svxlink. It supports all sorts of fancy things related to internet-linking, remote control, and automation, but you don't need to use any of that; it will also function just fine as a repeater controller for a standalone repeater, and periodic ID is one of the built-in features.

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  • $\begingroup$ I'm not sure how much I'm willing to spend at this point -- and I'd still have to solve the problems of where to put it, how to power it, how to protect it, and how to meet the Part 97 requirements for continuous monitoring and three-minute shutdown if control connection is lost. But a Pi or equivalent and USB accessories isn't likely to cost any more than the proper/legal repeater controllers I've been seeing. $\endgroup$
    – Zeiss Ikon
    Mar 28, 2019 at 16:05
  • $\begingroup$ A raspberry pi is really not a wise solution to this - fragile (especially the SD card if power is frequently lost), power hungry, expensive, and over complex. This is a task that calls for a small MCU, which is the way it's been being solved since the 1980's. And even if you use a pi, there's no reason to run the user audio through it, just build a trivial mixer. $\endgroup$
    – Chris Stratton
    Mar 28, 2019 at 16:14
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    $\begingroup$ @ChrisStratton that's fair, but there are advantages to doing it this way as well — it's easy to build in a day from readily available parts and you have access to the fancy features if you do want them. A pi zero (which would do fine for this purpose) should pull about a watt and costs $5, and it's entirely possible to run it with a read-only root fs (avoiding data corruption issues), although that isn't done nearly often enough. $\endgroup$
    – hobbs - KC2G
    Mar 28, 2019 at 16:27
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    $\begingroup$ It's a common but false misconception that a read-only file system makes an SD card safe for embedded use. In actuality it does not, as the invisible flash translation layer still does housekeeping on its own initiative - modern MLC cells require that it do so. Cards are sold to hold your vacation pictures in a battery powered camera that shuts them down with fair warning, they're really not engineered for embedded use. $\endgroup$
    – Chris Stratton
    Mar 28, 2019 at 17:19
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    $\begingroup$ @ChrisStratton I do understand that, but at the same time, a card that hasn't taken a write since power-on is going to have much less "housekeeping" to do than one that's receiving a constant stream of writes. It's no guarantee, but for personal use... it generally works okay. $\endgroup$
    – hobbs - KC2G
    Apr 7, 2019 at 5:02
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Many repeaters are not based on radios with built-in ID or any other repeater functions, but rather an ordinary transmitter and receiver (each possibly a transceiver used only for one function, if that's the most economical option) connected by a repeater controller through which the audio, PTT, etc. signals pass. The repeater controller knows how to ID (and to do so without interrupting usage of the repeater), generates the "courtesy tone" at the end of repeated transmissions, and may have remotely-controllable special functions (e.g. for repeater linking).

As I haven't built a repeater I can't recommend any specific examples, but I hope that you can find suitable products or project plans now that you know what to call them.

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You're not required to have an independent controller providing an ID.
As long as you can ensure the repeater does not transmit without IDing. You could ID the repeater yourself by just saying your callsign. When you ID the transmission on the input, the output provides identification as well. Per §97.119, a crossband system would need an ID transmitted on each input (UHF and VHF) since a true crossband repeater is bidirectional and actually has two transmit frequencies.

Edit: Automatic Control

Repeater controllers provide several functions to a repeater system. One is ID. The other is they will implement a system to comply with §97.109(d). Part 97 no longer gives specific direction on how to accomplish automatic control. Alot of the things repeater controllers implement in terms of automatic control are leftovers from past revisions of Part 97. This is detailed in Repeater and Auxiliary Control on the Repeater-Builder website.

It is generally accepted as a best practice to have an alternate means of turning off the system remotely. This could easily be accomplished with a second receiver and a DTMF controller. Alternatively, if your repeater location has internet access, you could use a WiFi controlled outlet.

I should add that this only applies to the United States.

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    $\begingroup$ This needs a rules section citation, since it seems to contradict the exam study materials and other answers. I'd be delighted if this being legal were as simple as using an oddball tone and offset to avoid others keying the repeater, but I doubt it's that simple or these would be all over the place. I can't be the only ham with major terrain issues... $\endgroup$
    – Zeiss Ikon
    Apr 4, 2019 at 11:05
  • $\begingroup$ I cannot reference what is not there. Nowhere in §97.119 does it specifically say a repeater must ID through automated means. It is done in practice because other people will (illegally) kerchunk a repeater and/or cannot be relied on to say the repeater's callsign. If you're the trustee of the repeater, then the repeater's call is your call. Your ID will be retransmitted, IDing the repeater. $\endgroup$
    – Reid Crowe
    Apr 4, 2019 at 12:53
  • $\begingroup$ Your edits are a big improvement. Thanks. $\endgroup$
    – Zeiss Ikon
    Apr 4, 2019 at 13:35
  • $\begingroup$ The gotcha here is that in the typical two-way "cross-band repeater" scenario, you need to ID into both inputs (the side that you would normally use, and the side that people use to talk to you) so that the repeater IDs on both outputs. Otherwise it's transmitting on one frequency with no valid ID. Any time someone keys up that side, even if you're not talking, you have to make sure to provide an ID. And, of course, you can't leave the thing turned on if you're not monitoring it to provide ID. So automation does make compliance much easier. $\endgroup$
    – hobbs - KC2G
    Apr 7, 2019 at 5:20
  • $\begingroup$ @hobbs-KC2G, you are correct that any transmission must ID. You are also correct that the best practice is to have the ID be automated. There is no legal requirement however on how to accomplish this. I'm simply stating what is legally allowed as interpreted by a non-lawyer engineer. Ultimately is is up to the end user to implement policies, procedures, and technical controls that ensure they comply with Part 97. $\endgroup$
    – Reid Crowe
    Apr 9, 2019 at 11:01

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