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[aprssig] Fill-in Digis

Ian ZL1VFO zl1vfo at yahoo.co.uk
Sun Mar 26 12:02:42 UTC 2006

> Message: 37
> Date: Sat, 25 Mar 2006 10:09:46 -0700
> From: "Stephen H. Smith" <wa8lmf2 at aol.com>
 ~~ Snip ~~
> I've had the same experience.  The TNC2, no matter what kind of enhanced
> DCD is added,  is useless for Mic-E-on-voice-repeater  applications.  It
> simply false-detects on voice peaks and DTMF signaling constantly.
Hmm, How do the MFJ1270/1278 fare by comparison? If poorly, can they
be improved somehow?

> Oddly one brute-force approach to DCD, borrowed from the past works
> fairly well.   I built a high-Q passive single tone filter using  a
> tuned circuit made of a classic 88mH toroid and styrene capacitors, in
> the style of early RTTY terminal units.  I resonated the toroid at 1200
> Hz, yielding a bandwidth narrow enough that only the low tone of a
> packet burst had significant energy within the passband. Voice energy
> and DTMF were ignored completely.    Total parts:   1 88mH toroid, two
> styrene or mylar caps, an LM324 op-amp, three resistors and a diode.
You wouldn't have drawn up a circuit, by any chance? I can think of a
couple of configurations off the top of my head, although I'm
interested in the method that has been shown to work...


> Stephen H. Smith    wa8lmf (at) aol.com

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