[App_rpt-users] Simulcast (was: posted on repeater builder)

Jonathan Weirmeir jonathan.weirmeir at gmail.com
Wed Feb 13 22:59:54 EST 2019


Could this device give new life to old crystalled repeaters, such as
Motorola Micor, GE MASTR II, etc? If so, anyone have any notes to share?

73 DE KC8RYW

On Wed, Feb 13, 2019, 2:59 PM Bryan Fields <Bryan at bryanfields.net wrote:

> On 2/12/19 10:05 PM, Pierre Martel wrote:
> > http://qrp-labs.com/progrock.html
> >
> > looks like this could maybe usefull on multicasting???
>
> Simulcasting is what this would be called.
>
> There are a number of issues with simulcast, disciplining the transmitter
> is
> just one of them.  This looks like it uses the 1pps output, not the 10 mhz
> output from the GPS, which will not have the resolution to lock the
> reference
> properly.
>
> The SI labs chip used in the PCGM used the 10 mhz output, but these had
> their
> own issues too.  The digital clock generators are harmonic rich, and really
> need filtering to be used.
>
> The traditional way to use the RTCM/voter is to remove the crystal
> reference
> on the transmitter PLL replacing it with the generated GPS clock.  In most
> radios this will remove the dual point modulation provided by a diode
> across
> the crystal.  Now modulation balance will be way off, and it will be much
> harder to get audio to line up.
>
> Most stations which have provisions for external reference already will
> use a
> 10 MHz or 5 MHz clock and lock the reference to that.  The Quantar and Tait
> will handle this just fine.  I'm been looking at the CDM radios (waris) for
> this too, as they use dither modulation of the reference frequency.  I've
> not
> had time to look further into it.
>
> The other issue is the audio needs to be delayed the same through each
> transmitter.  Some DSP based transmitters (SLR repeaters, etc) have a
> non-deterministic delay in the audio.
>
> 73's
> --
> Bryan Fields
>
> 727-409-1194 - Voice
> http://bryanfields.net
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