[App_rpt-users] RTCM 9.6 MHz OCXO

[Joe Moskalski]

---------- Forwarded message ----------
From: "Joe Moskalski" <kc2irv at gmail.com>
Date: Sep 10, 2016 1:37 AM
Subject: RTCM 9.6 MHz OCXO
To: "app_rpt mailing list" <App_rpt-users at ohnosec.org>
Cc:

I felt I needed to let those on this mailing list know my findings with
> simulcasting with the RTCM units since I have received a great deal of help
> and information from people on this list.
> For the past week I have had a two (2) site simulcast system up and
> running on UHF using the RTCM units. I have done a great deal of testing
> and proving on the bench and it is so far working beautifully. The one
> issue that was made apparent to me early on was that in order for the
> RTCM's to be suitable for simulcast, the processor inside it needed to be
> clocked to a more accurate source. This source is supposed to be the
> Programmable Clock Generator Module in order to produce a GPS locked 9.6
> MHz reference for the processor. Unfortunately this unit is not currently
> available.
> Knowing this, I started to go down the road of possibly designing my own
> but stumbled upon a cheap, plentiful supply of Symmetricom 9.6 MHz sinewave
> OCXO's. I took a chance and ordered a few to experiment with to see if the
> RTCM would be able to use this in place of the supplied crystal for a
> clock. I found they did, with that I decided to modify the RTCM with an SMA
> connector just about the audio adjustment pots and use this OCXO. I trimmed
> the frequency on the units to match each other and used them to produce the
> processor clock.
> After a week of testing I have found the results in the overlap areas to
> be exactly as I would expect them on a public safety/commercial simulcast
> system. While in an overlap region where both transmitters are within 3 dB
> of one another, to the ear you hear no audio phase wandering. Of course
> this has only been a week of testing so I wouldn't call it case closed yet.
> I will say that if this system remains this way after testing for 6 months
> to a year than using a 9.6 MHz OXCO is a viable alternative to achieve the
> needed precision and accuracy needed for the processor clock to make it
> suitable for simulcast.
>
> If anyone has any questions about my system feel free to contact me. i
> will more than happy to share everything I have done with anyone.
>
> Thank you to all on the list that contribute.
>
> 73's for now
> Joe
> KC2IRV
>
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