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8100xt2 pilot issue

O

OKCRadioGuy

I have a friend that has an 8100 with the xt2 chassis. The stereo pilot seems to wander from 3 to 10 percent every minute or so. I have exchanged out the stereo card with another 8100 but it still seems to do it. Would the power supply be the next step? Has anyone else experienced this before?

Thanks!
 
I think you are on the right track. EVERYTHING in the Optimod is referenced to its power supply and its design (especially the negative supply) is a holdover from the original 8000A Optimod and a piece of crap. Replace all the small capacitors on the power supply board with 105 C capacitors. I also like to hang a couple of 1000-2000 uf 35 volt capacitors right on the power supply where the wires go over to the big fliter capacitors (see what I mean about a crappy design? These long wires are in series with the filter caps.). I know it's tight in there but it can be done and still have room for the circuit cards to plug in. Also, always set the vlitage output to EXACTLY 15.00 volts (using the 10 turn trimmer) measuring the positive supply wth a digital voltmeter of known accuracy-do NOT use the negative supply for setting the trimmer. There's no way to adjust the negative supply-in theory it tracks the positive one, but it can be as much as a volt off from it in my experience.
 
One other out-of-box idea to check: if your friend is running RDS, and the RDS carrier is injected into a separate port on the exciter -- versus sending the output of the Optimod through the RDS encoder for carrier addition -- make sure the encoder is set for "sidechain" mode.

What you want to avoid is sending the composite into the exciter twice. I'm not saying that I would have ever done this, for example, when I was at a transmitter and was tired ::) but "somebody told me" that the results are weird. I know I can tell ... uh, I mean that guy who told me about it said that you can first see it in the pilot.
 
Thanks for the ideas guys! I will have him unhook the RDS and check it first before I tear into the Optimod, changing the caps and adding... THANK YOU to you both for the help!
 
Like the above poster said, you could have the problem if you connected the RDS encoder for the side-chain operation, but failed to configure it for side-chain and instead left it in the loop-through mode. The pilot that is sent to RDS for synchronization in that case won't be used for sync at all, but would be passed through to the output and get mixed in the exciter/processor with the MPX signal from the processor (which also contains the pilot). If there are changing phase issues, the two pilot tones would interfere.

The other possibility might be that you have a stereo generator built-in the transmitter, but you failed to turn it off/remove it from circuit. There might not be any audio signals present in the built-in stereo generator, but it would be outputting pilot tone that is probably just summed with the MPX signal coming from your processor. The two signals would most certainly not be in phase, which would cause the pilot to be modulated. I've ran into problem like this before on one radio station where they had the problem of losing stereo and, of course, blamed it on their Omnia. It turned out they had the stereo generator turned on in the exciter.


Regards,
Goran Tomas
 
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