[App_rpt-users] Simulcast buffer value issue

[Jeff Carrier]

I really hope to be able to confirm this soon.  I've been lazy and our 3
sites are 86 miles, 79 miles and 70 miles (in a triangle).  One of the 3 is
over 11,000 feet elevation.  No matter what we've tried so far you still
hear distortion in the overlap area(s) even when 1 site is 20 miles out LoS
and the other is around 60 miles out non LoS.  Everything is linked on a
private uW network with very low latency and basically zero packet loss.
The transmitters (GE MIII) run about 1hz freq error with the gpsdo attached.

Sometimes I just wonder if this is just multi-path from the various granite
reflectors we have on the front range of Colorado (one of them is Pikes
Peak)

de K0JSC

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>
> Message: 6
> Date: Tue, 13 Feb 2018 20:43:42 +1100
> From: Hayden Honeywood <haydenph91 at gmail.com>
> To: app_rpt-users at lists.allstarlink.org
> Subject: [App_rpt-users] Simulcast buffer value issue
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> Interesting thoughts Tim... perhaps worth documenting on the wiki?
> Even though it was just "in theory", what kind of sync error was it?
> Were we talking microseconds or even more?
>
> I have a receiver on a yagi pointed at a distant simulcasted site. I
> have noticed on occasion, I can hear the distant simulcasted site
> start to send audio underneath the carrier of the site that is closest
> (and strongest to me). The distant site is also the master site, and
> has the lowest latency, but I'm talking two words worth of audio is
> send before my other site starts sending audio. Once they are both
> transmitting, I  have not noticed any timing issues (i.e. distortion
> etc). I'm not sure if this issue was related to what I posted
> previously about the variable audio delay on unkey.
>
> I'm running app_rpt on a Raspberry Pi using a cut down image we use here
> in VK.
>
> http://vklink.com.au
>
>
> "When simulcasting the audio from all (non captured) transmitters needs to
> arrive at the receiver with in an acceptable time frame (80 us). The DAC
> theory was that it didn't start sending audio at correct clock cycle every
> time. That would cause the audio to be out of sync between RTCMs causing
> simulcast distortion.
>
> As I said, that was the theory. The new theory is that the external clock
> source was causing the DAC to trigger inappropriately. I spoke with someone
> I met here on the list (Kevin I think its was) who is using a different
> external clock and reports perfect simulcast operations"
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