Batboard

Hi Group,
I've got a UHF Micor RT station with SpectraTAC voting that's worked fine for years, with only one issue: The repeater doesn't encode reverse-burst onto the end of the transmissions. It's been this way since I bought it. It doesn't matter if I disconnect the SpectraTAC comparator, etc; it still doesn't transmit reverse burst.

Any ideas what this could be? I seem to recall there's some feature that allows you to disable reverse burst, but why someone would want to, I don't know. I've scoured the manual, and I can't find anything plainly there about it. I'd like to get rid of the squelch tail when the repeater unkeys on the radios. Any guidance is appreciated.

Did you do steps in the troubleshooting chart for this symptom?

i.e.

Check for 170-250 ms delayed keyed A+.
Check for turn off code @ U801-5.
Check to see if low pass filter is always switched low [defective Q705]

No, I didn't check these things. Where in the manual is this procedure detailed?

Which cards could possibly be causing this problem? Is there a jumper somewhere that can enable/disable reverse burst? This thing was pretty heavily modified for use with an aftermarket controller, and I did my best to restore it to factory defaults, but I could've easily missed something.

Usally the ENCODER for the PL is in the Exciter plugged into the back side of the board. You can unplug the Encoder board, TURN OFF THE POWER first, and plug it into the frontside of the Exciter for testing. Look for Delayed A+ to the Station Control board, in the card cage on Pin 13. The Delayed A+ comes from the Transmitter on Pin 27 into the card cage. It originates on the PL or DPL Encoder plugged into the Exciter.

You may have a non stock Encoder, BTW the Encoder is the same as in the Micor mobile.

The encoder is the stock MICOR repeater encoder board, the type that uses a plug-in vibrasender reed to determine the PL frequency.

I'm unclear on what to look for with regards to the delayed A+. What parts should one start replacing if they don't want to go down to component-level on this? Encoder board? Station Control Module? Squelch Gate? Line Driver? Thanks for the help.

Maybe I was not too clear.. Keyed A+ from the Station Control goes up to the PL Encoder in the Exciter. When this switched or "Keyed A+ goes away when the PTT is released, the Delayed A+ is generated in the PL ENCODER during the reverse burst time, aprox. 180ms after PTT goes away. PTT going to the EXCITER is accually the Switched A- from the Station Control Board, pin 7. The DELAYED A+ keeps the TX keyed while the PL reverse burst is transmitted, and returns from the PL Encoder board thru the Exciter to pin 13 on the Station Control board, where the Switched or Keyed A- is kept switched. Look at the DELAYED A+ with a scope and trigger on the PTT line going positive, the end of PTT.

Then look to see if the DELAYED A+ is accually getting to the Station Control card pin 13, that is where the PTT , switched A-, to the Transmitter is streached the aditional 180ms, so the Transmitter stays on to transmit the PL reverse burst.

Also check the ENCODER to see if any componets have been removed or "butchered".

My two bits worth:
I have seen this! (Over 30 years ago)

I can't recall exactly which jumper was missing from the factory.
Perhaps Reverse burst timing does not always come from the PL encoder.
I think the wrong jumper was on the station control module.
The early (Prior to the unified chassis) had a fold out overall diagram that was very useful in figureing out which jumpers go where.

Be sure the jumper on the exciter board in the PTT line is open for PL operation. (JU405)

I don't think that the Spectra Tac encoder has anything to do with this problem.

BTW. The mobile PL board looks the same but is not directly interchangeable. The tone level output on the mobile version is greater, and you will really have a PL buzz. I discovered this while trying to figure out the problem with missing Reverse burst. It will do for trouble shooting.

Bernie,
Thanks for the reply. It's a unified chassis unit. I'm concentrating on installing the C269 SpectraTAC Encoder option right now (XMO if you're reading, I ordered and received the manual, and the cards are on the way), I'll take care of the reverse-burst issue next.