[App_rpt-users] Simulcast buffer value issue

Thu Feb 15 19:50:57 UTC 2018

It did. I saw it.

You know, it would seem to me that timing really isn't the issue as much as
the xmtr frequency being exact at all three sites. Although, on FM, the
frequency is modulated at the same rate in the overlap areas, so I can see
where timing is critical, but unless all 3 xmtrs are synched to the same
frequency, it's still gonna sound like a jumbled mess...

The answer isn't simple, but it looks like you're either going to have to
reduce transmit power output or incorporate low-gain directional antennas
for the transmitters.

Lower gain transmit antennas a few (hundred?) feet down from the RX
antennas?

Just tossing some thoughts out there.

Good Luck, Jeff.

On Feb 15, 2018 12:53 PM, "Jeff Carrier" <k0jsc.jeff at gmail.com> wrote:

...I'm not sure that mailman passed the image.  If you're interested I can
send it off list.

On Thu, Feb 15, 2018 at 11:50 AM, Jeff Carrier <k0jsc.jeff at gmail.com> wrote:

> 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.gm
>> ail.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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