Early work[ edit ] In three Bell Labs researchers, Stephen.
WB6SOX here, someone pulling my chain? What happened was that Ralph had his radio in tone decode mode and was not hearing any of the conversation on the repeater.
Note that Ralph does not have a DTMF decoder - he has a plain-jane radio that happens to have a tone decoder feature. All the hard work is done in the repeater.
The text above mentions a DTMF decoder pulling in a relay, because that's how the first one was implemented - a Speedcall brand DTMF horn-honker decoder that had been retired from IMTS service drove one coil of a two-coil latching relay.
The COR pulsed the other coil. The contacts operated the tone encoder. These days it can all be implemented in the repeater controller - and while any modern controller can do PL Paging, the Scom 7K no longer in production actually has a tone encoder audio gate built into it and you'd think it was designed just for the job.
It also has 6 digital outputs that are designed to be wired to the tone control leads of a TS or TS or any other similar tone encoder. From another email to repeater-builder: The users of such systems would quickly find a Morse code ID every N number of minutes to be very annoying.
All of my repeaters no matter what service strip the encode tone during ID, and nobody ever hears an ID. Many of the Hams who use my repeaters have commercial-quality radios with full-time PL decode, and they are very happy to not hear the ID or any squelch crashes. If you are setting up radios from multiple manufacturers on a common channel like for a neighborhood CERT team do not mention the tone numbers from the radio like "use channel 14 and tone 10" in your procedures manual or in your deployment instructions.
Use the tone frequency instead. The problem is that what is tone 12 on one brand might be tone 13 on another, or tone 43 on a third, or tone Look at this page for some examples of non-compatible tone numbers there are six different tone 38s just on that page.
Even the FRS manufacturers can't get it right, and while the information on this spreadsheet-style page is dated several models mentioned are no longer produced or soldit does makes the point Many older system engineering books recommend using every other tone.
This came from experience gained in the mid s through the late s due to three reasons - the close spacing of the tones, tone encoder start-up drift and the early decoders had a wider bandwidth and would false on adjacent tones. Many cheaper radios still have that falsing problem today, mainly because the lower frequency tones are spaced closer together percentage than the higher tones.
If you look at the web page at http: The early books suggested selecting either Group "A" or "B". Many phase-modulated transmitters have trouble sending the tone at the proper level across the entire tone range. The lower frequency tones are often lower in level as the modulator components are selected to prevent the higher tones from being over-deviated.
The lower frequency tones end up being under-deviated and hence difficult to decode reliably at the other end. True FM transmitters don't have this problem. Lower frequencies are easier to filter out of the voice audio stream.
Another reason to avoid low frequency tones is if you are using a toned repeater and tone decoders in the mobiles. It gets progressively worse if you have toned links between repeaters creating longer and longer decoder chains. Higher frequencies decode faster. Basically the decoder, be it a vibrating reed or a microprocessor, needs some minimum number of cycles of tone to assure accurate decoding.
In reality, many real hardware decoders are very close to milliseconds at You want to avoid tones that are harmonically related to local AC mains power.
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