Maker Pro
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todays Ham Radio meeting..

J

Jamie

Jan 1, 1970
0
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
 
W

Winston

Jan 1, 1970
0
Jamie said:
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.

You're lucky!

If I wanted one of the interfaces I designed
for Xerox in '94, it'd cost me a bundle:
http://www.l7inc.us/info_123

--Winston
 
J

Jamie

Jan 1, 1970
0
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
 
N

Nico Coesel

Jan 1, 1970
0
Jamie said:
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.

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.
 
J

Jamie

Jan 1, 1970
0
Nico said:
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.
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
 
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