[App_rpt-users] RTCM Simulcast question

[Sam Skolfield]

Jesse,

>From my understanding as well as many others, simulcasting WON'T work
properly in overlap areas unless you replace the RTCM's internal 9.6MHz
crystal with a GPSDO 9.6MHz @3.3 volts p-p. If you expect a cheap 9.6MHz
crystal to derive a 1PPS signal and stabilize it between clock pulses down
to a level acceptable for accurate syncing of CTCSS generation, free of
intrinsic jitter, you are "optimistic" to say the least.

Jim Dixon has articulated this before on the email list. Simulcasting with
the RTCMS in overlap areas WON'T WORK PROPERLY without this trivial
modification. Obviously this requires usage of IDENTICAL equipment at each
site. Here is a pointer to an email of his.



*http://ohnosec.org/pipermail/app_rpt-users/2013-November/007704.html
<http://ohnosec.org/pipermail/app_rpt-users/2013-November/007704.html>*
Jim described a possible future RTCM design with convenient provisions for
plugging in external 9.6MHz, but this has not happened.

73



On Sun, Jun 5, 2016 at 1:04 PM, Jesse Lloyd <ve7lyd at gmail.com> wrote:

> You need both 1 pps and Rx GPS data to the RTCM
>
> Cheers,
> Jesse
>
> On Jun 4, 2016, at 6:03 PM, Joe Moskalski <kc2irv at gmail.com> wrote:
>
> I will be setting up a 2 site UHF simulcast system in the coming months
> and so far I have only one question to ask. The RTCM manual is a little
> vague on the GPS part of the setup. Normally, with other types of radio
> simulcast products (which I am very familiar with several) all you need to
> properly time the audio is a 1 pps signal from the GPS reference. The RTCM
> manual makes mention of the NMEA/TSIP data being connected but does not
> explicitly say if that serial data is needed or if only the 1 pps is needed
> for simulcast operation. From the other simulcast products I have worked
> with, you set your bulk delay to a value larger then the delay required for
> the furthest site and the system will adjust. Does the RTCM version of
> simulcast work the same way? I just want to be sure because this will
> determine what type of GPS locked reference oscillator I choose for the
> project.
>
> Regards,
> KC2IRV
> -Joe
>
>
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-- 
KJ6QFS
Sam Skolfield
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