[App_rpt-users] RTCM Simulcast question

[Lee Woldanski]

Just throwing this out there... wouldn't it be possible (trivial?) to
configure the PIC (firmware) for 10MHz external clock, and replace the
9.6MHz crystal with 10MHz in from a GPSDO?


Lee

On Sun, Jun 5, 2016 at 1:33 PM, Sam Skolfield <kj6qfs at gmail.com> wrote:

> 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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-- 
Lee Woldanski, AScT
VE7FET
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