[App_rpt-users] Simulcast buffer value issue

[Kevin Walsh]

Have you looked at Joe, KC2IRV's website? He has done some extensive experimenting with simulcast. I found it helpful.

Http://rtcmsimulcast.wikifoundry.com

Kevin
W8KHW

> On Feb 13, 2018, at 11:10 PM, Jeff Carrier <k0jsc.jeff at gmail.com> wrote:
> 
> 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
> 
>> ------------------------------
>> 
>> 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
>> Message-ID:
>>         <CAC0VLD0-9mc=T8BkvMwx6PqWXqtUXCYY2odbjc2ajjDiVLKSBg at mail.gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>> 
>> 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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