[App_rpt-users] Simulcast buffer value issue

[Jeff Carrier]

Here's a down and dirty display of overlap with transmitter power, feed
line loss, antenna gain, pattern and azimuth figured in.

[image: Inline image 1]


> Message: 8
> Date: Wed, 14 Feb 2018 17:33:50 -0800
> From: Tim Sawyer <tisawyer at gmail.com>
> To: Users of Asterisk app_rpt <app_rpt-users at lists.allstarlink.org>
> Subject: Re: [App_rpt-users] Simulcast buffer value issue
> Message-ID:
>         <CAG3ht9t7Unky+Tc0MFTOLg2Z3+pcnoWFM2AyNFKeFcrOeE4cdw at mail.
> gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> 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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>
>
> --
> Tim WD6AWP
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