RTCM Simulcast question

App_rpt-users
1

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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2

Hi Joe,

I can answer part of that for you.

You do need a GPS with NMEA or TSIP. The RTCM needs to know the time so it can time stamp the UDP packets when sending them to the server.

If you go to http://svn.ohnosec.org/viewvc/projects/allstar/voter/?root=svn and look at the VOTER Protocol.pdf and the votersystem.pdf, and look at the protocol parts, you may answer some of your questions.

I know the required NMEA sentences are out there somewhere, but I don’t recall where I saw them.

You can adjust the launch delay on each RTCM, but I do not believe it does any sort of auto adjust.

Lee

···

On Sat, Jun 4, 2016 at 6:03 PM, Joe Moskalski kc2irv@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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VE7FET

3

While I don’t have any hands on experience simulcasting with RTCMs, I do understand something that is not really documented, only to be found in the depths of the email posts.

If you want reliable simulcast with an acceptable level of overlap warble, you MUST inject a GPS-disciplined 9.6MHz signal to the clock of the RTCMs in leu of their stock internal crystal. Otherwise, the inherent internal clock jitter of the RTCMs will cause CTCSS warble, etc in areas where your transmitters overlap. The 1PPS feed that you normally feed the RTCMS is acceptable for voting, but naturally, a typical crystal-driven clock will slightly drift in between the pulses every second due to inherent jitter, etc, and that ain’t to good for situations like simulcast which demand sample-accurate performance.

If I have misspoken about anything, I apologize and relish the opportunity to be re-educated.

73
SS

···

On Sat, Jun 4, 2016 at 6:03 PM, Joe Moskalski kc2irv@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

4

Hi Joe,

Copying the list so they see your update/questions.

As for votemond/votermon, yes, go with Allmon2. Easier to configure, and many more features at your disposal. :slight_smile:

Lee

···

On Sat, Jun 4, 2016 at 6:21 PM, Joe Moskalski kc2irv@gmail.com wrote:

Ok, thank you, now I can be sure I get the correct GPS reference unit. Thank you for the link, I had not seen this before.

With this information I will be using this unit for my GPS data, 1pps and 10 Mhz. I have tested one of these it should will work.

http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Disciplined-Clock-GPSDO-Antenna-Power-Supply-USA-/281802105734?hash=item419cb6e386:g:to0AAOSwKIpV-hf7

Also does anyone know of someone who has successfully setup a simulcast system with the RTCM’s? I was just wondering if I could touch base with them and possibly avoid any common pitfalls.

Just in case any one was wondering I will be using Kenwood TKR-840 repeaters for this project.

Another question I have is there are references to the votmond java application for monitoring the system but I believe Allmon2 succeeds votmond, is this correct?

–

On Sat, Jun 4, 2016 at 9:09 PM, Lee Woldanski ve7fet@tparc.org wrote:

Hi Joe,

I can answer part of that for you.

You do need a GPS with NMEA or TSIP. The RTCM needs to know the time so it can time stamp the UDP packets when sending them to the server.

If you go to http://svn.ohnosec.org/viewvc/projects/allstar/voter/?root=svn and look at the VOTER Protocol.pdf and the votersystem.pdf, and look at the protocol parts, you may answer some of your questions.

I know the required NMEA sentences are out there somewhere, but I don’t recall where I saw them.

You can adjust the launch delay on each RTCM, but I do not believe it does any sort of auto adjust.

Lee

On Sat, Jun 4, 2016 at 6:03 PM, Joe Moskalski kc2irv@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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Lee Woldanski, AScT
VE7FET

–

Lee Woldanski, AScT
VE7FET

5

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@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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6

Jesse,

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

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@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@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

7

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@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

Jim described a possible future RTCM design with convenient provisions for plugging in external 9.6MHz, but this has not happened.

73

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–

On Sun, Jun 5, 2016 at 1:04 PM, Jesse Lloyd ve7lyd@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@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

–

Lee Woldanski, AScT
VE7FET

8

And that is why I leave software to the smart people… :slight_smile:

Thanks Jim!

Lee

···

On Sun, Jun 5, 2016 at 11:17 PM, Jim Duuuude telesistant@hotmail.com wrote:

NO

From: app_rpt-users-bounces@ohnosec.org app_rpt-users-bounces@ohnosec.org on behalf of Lee Woldanski ve7fet@tparc.org
Sent: Sunday, June 5, 2016 10:22 PM
To: Sam Skolfield
Cc: app_rpt-users@ohnosec.org
Subject: Re: [App_rpt-users] RTCM Simulcast question

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@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

Jim described a possible future RTCM design with convenient provisions for plugging in external 9.6MHz, but this has not happened.

73

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Lee Woldanski, AScT

VE7FET

–

On Sun, Jun 5, 2016 at 1:04 PM, Jesse Lloyd
ve7lyd@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@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

–

Lee Woldanski, AScT
VE7FET

9

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@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@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

Jim described a possible future RTCM design with convenient provisions for plugging in external 9.6MHz, but this has not happened.

73

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You do not need a password to unsubscribe, you can do it via email confirmation. If you have trouble unsubscribing, please send a message to the list detailing the problem.

–

Lee Woldanski, AScT
VE7FET

On Sun, Jun 5, 2016 at 1:04 PM, Jesse Lloyd ve7lyd@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@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

–

KJ6QFS
Sam Skolfield