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=RTCM Simulcasting=
=RTCM Simulcasting=
The RTCM/VOTER boards do support simulcasting, however, there are a bunch of quirks that one needs to be aware of.
The RTCM/VOTER boards do support simulcasting, however, there are a bunch of quirks that one needs to be aware of.
==Radio Hardware==
For best results, you should use all identical RF equipment between your voting RX sites and simulcast TX sites. If you don't, you can end up with strange audio artifacts when different receivers are used, and other strange audio issues when different transmitters are used.
:We had to use 9.6MHz mainly because of the DAC in the dsPIC instead of 10MHz. The options for various divide/clock radios in the part are RATHER limited. As I recall, there wasn't even a way of getting the necessary 16kb/s sample rate on the ADC from 10MHZ, either.
:We had to use 9.6MHz mainly because of the DAC in the dsPIC instead of 10MHz. The options for various divide/clock radios in the part are RATHER limited. As I recall, there wasn't even a way of getting the necessary 16kb/s sample rate on the ADC from 10MHZ, either.
=Micro-Node RTCM Clock Issue=
James, KI0KN, had some strange-ness with some of his RTCM's when used for voting. As soon as he changed menu item 10 on the RTCM to either a (1) or a (0) instead of (2), he '''instantly''' got this on the RTCM console:
<pre>
04/05/2016 18:44:13.660 Lost GPS Time synchronization
04/05/2016 18:44:13.660 Host Connection Lost (Pri) (10.16.1.240)
</pre>
And it sits there forever and never re-establishes connection to the host. The issue was finally traced to a bad batch of 9.6MHz crystals that affected a small run of the RTCM's. The issue was eventually resolved by Micro-Node, but we'll document it here just for record keeping.
James comments to the list:
:Well, after many of you offered your time and thoughts on my voter problem, Jim, WB6NIL, graciously donated a couple of hours of his time to remotely help me and he uncovered the problem.
:All 5 of my RTCMs were purchased within the last 6 months, and I suspect all 5 have the same problem (will verify that today). The problem is that the microprocessor crystal is running too fast! There is 9.6Mhz crystal that drives the MPU, on the particular unit that Jim helped me diagnose, it's running 2.5 khz too fast.
:There is a sanity check in the firmware that makes sure the correct number of samples were taken in the last second (it's supposed to be 8000) and fails if the sample is incorrectly sized (mine is taking 8003 samples). Jim helped adjust the code to be more tolerant of the sampling error and my whole system instantly worked.
:I have since tested it with ALL my GPSs (they all work great!). So I now have everything working, including the voting.
:I haven't contact Micro-Node about it yet. Jim told me that voting should work fine but this clock error would probably not be acceptable for Simulcast (something we have no plans on doing as of now). Since mine are deployed at mountain top sites, I'll probably pursue a crystal that is running at the correct frequency and use "standard" firmware so that if the decision is ever made to play with simulcast, I won't be right back in this same boat.
:Thanks to all that helped out, and a HUGE thanks to Jim for taking the time to troubleshoot this.
:BTW- This clock error will NOT effect the RTCM in mix client mode, it only affects it in voting or simulcast mode!
:In voter.c, the stock line is:
<pre>
if ((samplecnt >= 7999) && (samplecnt <= 8001))
it needs to be changed to something like:
if ((samplecnt >= 7999) && (samplecnt <= 8003 ))
</pre>
:That was just enough to make my first RTCM work. I've had a chance now to check a few more of my RTCMs on the bench this morning and the crystal frequencies are kind of all over. The next one I had on the bench was 5.2Khz fast. The above code was still not enough to fix it (as would be expected) so it looks like the quality control on whatever manufacturer that crystal is, isn't very good (or a low tolerance crystal is being used). I am going to pursue crystal replacement to get a highly accurate, stable, on-frequency crystal in there as my first choice. Changing the firmware 5 different times doesn't seem like the right answer.
:Jim put that sanity check in there for a reason. Working around it '''may''' allow the device to work, but to me, it seems getting the hardware operating the way it was supposed to originally is the better answer. I will follow up with Micro-node and let you all know how it goes.
After following up with Micro-Node:
:They were all off, some were off a LOT. I talked to Mark @ Micronode. He told me there were 25 units that made it out the door with a crystal from an unapproved source and that was quite likely the reason for the problem. He gladly sent me 5 new crystals to replace (he offered to replace them himself if I sent the units in, but I am comfortable doing it myself to save the time and postage).
:I haven't received them in the mail yet to show that the problem is fixed, but I will post here when that happens. He was great to work with and had no issue getting things set straight. If you are having the same issue and your RTCMs were bought about the same time, I'd suggest you contact him and have him help you resolve the issue!