[App_rpt-users] RTCM audio interfacing options

Sam Skolfield kj6qfs at gmail.com
Tue Jan 23 06:32:27 EST 2018


Greetings,
I've been playing with RTCMs and VOTER boards for almost 5 years now, and
I'm very happy with what I have in service. I've built a multi-site voted
system, and more recently a non-voted hub that ties together repeater
controllers at a few sites.

I'm helping a friend but together a RTCM / pair of GM300 repeater, and got
to thinking about audio options. There is more than one right way!

1. Discriminator audio to RTCM, set deemp=yes in voter.conf (causes
hardware de-emphasis in RTCM circuitry)
RTCM TX audio to GM300 Flat audio input, use chan_voter software
preemphasis by specifying txctcss and txctcsslevel=0 in rpt.conf

2. 1. Discriminator audio to RTCM, set deemp=yes in voter.conf (causes
hardware de-emphasis in RTCM circuitry)
RTCM TX audio to mic audio, letting radio do pre-emphasis.


3. 1.De-emphased audio from GM300 (JU551 set to B)  RTCM
RTCM TX audio to mic audio, letting radio do pre-emphasis.

4. 1.De-emphased audio from GM300 (JU551 set to B)  RTCM
RTCM TX audio to Flat audio input, use chan_voter software preemphasis by
specifying txctcss and txctcsslevel=0 in rpt.conf


All four of these combinations should theoretically produce "flat" system
response, but I'm sure all four yield slightly different results, given
different corner frequencies in hardware/software de-emphasis /
pre-emphasis and different input/output impedance combinations.

Has anyone experimented with these combinations?

73
-- 
KJ6QFS
Sam Skolfield
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