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

Tim Sawyer tisawyer at gmail.com
Mon May 8 23:10:38 EDT 2017


The PCGM were noisy. I know of a case where a ham using one was shut down
by the site owner. Seems the PCGM was emitting a interfering signal on high
band, around 158 Mhz.

On Mon, May 8, 2017 at 1:33 PM, Bryan Fields <bryan at bryanfields.net> wrote:

> 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 <(727)%20409-1194>
>
> 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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-- 
--
Tim
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