[App_rpt-users] RTCM Simulcast question

[Sam Skolfield]

Here's another link to some more info in an email thread.
http://ohnosec.org/pipermail/app_rpt-users/2015-December/013155.html

On Sun, Jun 5, 2016 at 10:22 PM, Lee Woldanski <ve7fet at tparc.org> wrote:

> 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
>



-- 
KJ6QFS
Sam Skolfield
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