[App_rpt-users] RTCM Simulcast and 9.6 MHz Phase locking

Bryan Fields bryan at bryanfields.net
Mon May 8 16:33:05 EDT 2017


I've been following this with some interest.  One of the fundamental issues with the PCGM was the master clock going to the radio was unable to be modulated.  This made low frequency signals (PL) distort, and digital PL was even worse.  

Typically most radios use two point modulation, with modulation on the reference oscillator.  When you add an external reference you loose this.

Some base stations are designed to do two point modulation even on an external clock, the Quantar for example.  This station will even phase lock it's PL and DPL generation if provided a 1 PPS in addition to a clock.

If we could inject modulation into the clock generator simulcast performance would vastly improve.  I'd be interested to see your design to see if this would be a possibility.

Thoughts?

--
Bryan Fields
M: +1-727-409-1194

> On May 8, 2017, at 14:15, Reid Brandon <rfpowerguy at yahoo.com> wrote:
> 
> Hi Joe,
> I got a page with a pic of a man that rotated  around saying DOWNLOAD NOT FOUND.
> Try again!?
> Tks  Reid
> 
> 
> On Sunday, May 7, 2017 12:25 PM, Pierre Martel <petem001 at gmail.com> wrote:
> 
> 
> I am very interrested in all this project. My email is VE2PF @ VE2MRC dot com!
> 
> what radio did you used for the project? 
> 
> Thanks for sharing!
> 
> Pierre
> VE2PF
> 
> 
> 2017-05-07 12:32 GMT-04:00 Kevin Custer <kuggie at kuggie.com>:
> Joe,
> 
> Why not consider do it as an article for Repeater Builder?
> 
> Thanks,
> Kevin
> 
> 
> On 5/7/2017 3:13 AM, Joe Moskalski wrote:
> I wanted to throw this email out to the group for all those who want to simulcast with the RTCM. For those who don't know, in order to make the RTCM suitable for simulcast you must have a more accurate 9.6 MHz clock for the RTCM in order to ensure the audio sounds acceptable in the overlap areas. I did this a few months ago using 9.6 MHz OCXO's. This worked reasonably well. Not as well as I would have liked but the system was very usable, but of course I wanted it to be better. Since the PCGM (Programmable Clock Generation Module) is no longer available, I decided to roll my own as some say.
> I created a PLL circuit that can accept a 10 MHz, 1 MHz or 100 KHz reference input and produce a phase locked 9.6 MHz out for the RTCM. I have been testing this over the past few days and it has made an great improvement in the audio quality in the overlap. The quality of the audio in the overlap areas sounds very, very good, it's very similar to what I expect to hear in commercial simulcast systems. My circuit is heavily based off of an old Motorola MSF5000 HSO PLL circuit that I was able to adapt and modify to my needs.  There are other uses for this circuit that make it attractive for simulcasting but I wont get into them here. I am will to share my schematic and bill of materials (digikey) with anyone. Please send me an email and I will be willing to share all of my information on the project.
> 
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