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.