[App_rpt-users] RTCM audio interfacing options

Jesse Lloyd ve7lyd at gmail.com
Tue Jan 23 10:41:30 EST 2018


Well, if you want it to vote it'll have to be discriminator rx audio. If not, I'll use which ever squelch I deem to be superior. The motorola 2 level squelches are typically pretty good, but you have to open the lid on a GM300 to adjust it. If that's ok, then I'd use that.  

For pre-emph, if you want simulcast with PL you have to let the voter make the PL tone. Otherwise I prefer using the mic in as it has nice a nice audio filter response and limiter circuit. Just a note for the GM300 you should adjust the max deviation when programming them into the ham band. The UHF ones I find change quite a bit with frequency. Sometimes you'll also have to make an adjustment to the PLL reference voltage to get it to lock up for Tx. 

Cheers,
Jesse

> On Jan 23, 2018, at 3:32 AM, Sam Skolfield <kj6qfs at gmail.com> wrote:
> 
> 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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