[App_rpt-users] Simulcast buffer value issue

[Tim Sawyer]

11,000 feet! No way that will simulcast well, not at 70 miles.

On Tue, Feb 13, 2018 at 8:10 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.gm
>> ail.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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>
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-- 
Tim WD6AWP
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