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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