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todays Ham Radio meeting..

We had an auction at our ham radio meeting tonight of stuff that has been sitting around and thought maybe it was a good idea to liquidate the un-needed items.

I got for $1.00 a repeater remote control unit with DTFM decoder that handled 16 lines of control that I designed and built ~ 25 years ago now.

This thing is still in operational shape even though it took some cosmetic reconditioning over the years at the 2 meter tower site. It even has a DTFM local keypad built in and made when they used to make them good!

I also picked up some other ancient relics of good value.

Its nice when you can get back your own creations of yesteryears.

Jamie

Reply to
Jamie
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un-needed items.

reconditioning over the years at the 2 meter

good!

You're lucky!

If I wanted one of the interfaces I designed for Xerox in '94, it'd cost me a bundle:

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--Winston

Reply to
Winston 

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Dual Tone Frequency Modulation?
Reply to
John Fields

TouchTone® by any other name...

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You can't have a sense of humor, if you have no sense.
Reply to
Michael A. Terrell 

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Ah, DTMF then.
Reply to
John Fields

yeah, guess I twisted my fingers around on that one, DTMF.

The keypad has a chip for it to generate it for local control but the detection side was 8 active band pass filters that generated a DC reference output to a 4 to 16 line mux.

Each DC output has a small cap on it that goes to a noise detection circuit. They are all tied together in a R network to a single common noise detector. That was used to insure a steady signal was there before the gate on the mux was enabled.

This was designed to work with high levels of noise and weak audio, which it did and still does for that matter.

Jamie

Reply to
Jamie

I wouldn't bet on it. Some people can talk DTMF tones by the dozens. You need really tight tolerances which cannot even be achieved by practical digital filters. Mitel (now Zarlink) used to have good chips for sending / receiving DTMF.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
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Reply to
Nico Coesel

Maybe, But my unit went through 3 repeater updates and replacements over the years.

And btw, we experimented with a few different chips over the years, they all worked, some very poorly, others ok.

I suppose with today's DSP technology on a chip, or uC's with enough horse power to perform that duty would do better in determining other stray signals in there that may make the tones invalid.

But, I did see a design years ago that I think really got out of hand even though it did work, but the over all advantage wasn't that much better. This design would use the images that made it pass the filters and then sum them with the incoming original signal to notch out the desired frequencies. The mixed results would then be sent through a circuit to determine if remaining signals were still significant and maybe assume that voice was in the mix and not consider the detected tones as being valid.

Doing this with analog can get bulky, doing it with DSP can be small but we didn't have DSP at that level back then.

Jamie

Reply to
Jamie

Yes. We built one in 1968 for the .01/.61 repeater in Monroe Ohio. It was one of the first reliable phone patches in the area. Sloman's favorite, the 555 wasn't available, so the various timers were built with PUTs. We even made the diplexer out of copper pipe.

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You can't have a sense of humor, if you have no sense.
Reply to
Michael A. Terrell

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