[aprssig] Fill-in Digis
bruninga at usna.edu
Sat Mar 25 20:21:58 CST 2006
The KPC-3+ has an additional MUTE setting for its DCD that
I asked Kantronics to add back when the Mic-E first came out.
It is designed specifically for nearly perfect packet versus
Voice detection. This is for a Mic-E PTT mode operation at
a voice repeater.
You can use the MUTE output to mute the output of the voice
repeater when an Mic-E PTT packet comes in. This way, users
of that repeater can operate APRS Mic-E on a single radio
Im not sure that sepecial Mute coding is in the 9612+?
>>> wa8lmf2 at aol.com 03/25/06 12:09 PM >>>
tim_cunningham at mindspring.com wrote:
> When selecting a packet controller to work as a packet decoder on our
> local voice repeater, I found the add-on TRUE-DCD board worked rather
> poorly with voice audio and it could not be utilized in muting the
> audio on the output of the repeater. This add-on board falsely
> triggered the mute control line to the point that it was very annoying
> to listen to a conversation on the output of the voice repeater. We
> then went to a Kantronics KPC-9612+ and it worked acceptably well. The
> add-on board for the TNC 2 clones may be adequate to work with open
> squelch radio outputs, but they are far inferior when using the DCD
> signal to mute audio on a voice repeater to prevent the packet data
> from being heard on the output of the voice repeater.
> The point is that the DCD decoding works much differently on the TNC2
> add-on (hardware decoding) versus the KPC (firmware decoding) units.
> Tim - N8DEU
> Huntsville, Alabama
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.
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.
Stephen H. Smith wa8lmf (at) aol.com
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