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

Joe Leikhim rhyolite at leikhim.com
Tue May 9 02:24:46 EDT 2017


I wonder what kind of enclosure he had it in?


On 5/8/2017 11:10 PM, Tim Sawyer wrote:
> 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 
> <mailto: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 <tel:%28727%29%20409-1194>
>
>     On May 8, 2017, at 14:15, Reid Brandon <rfpowerguy at yahoo.com
>     <mailto: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 <mailto: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
>>     <mailto: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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-- 
Joe Leikhim


Leikhim and Associates

Communications Consultants

Oviedo, Florida

JLeikhim at Leikhim.com

407-982-0446

WWW.LEIKHIM.COM

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