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RT97s to ID-O-Matic interface problem



I' m having a problem with the COR out on the RT97s to COR in on the ID-O-Matic (latest version). The repeater trips the controller OK but the controller produces a voltage that back feeds into the RT97s COR circuit causing problems. One of the problems is a loud white noise being transmitted. Sounds like an open squelch. Disconnecting them and manually tripping the controller and the problem goes away. Courtesy beep works as it should and the loud white noise vanishes that the repeater was broadcasting. It appears some kind of isolation circuit is required like a reed relay or maybe a MOSFET. Anybody run into this problem? What was your solution? The COR on the RT97s goes low on carrier detect. The controller is expecting it's COR input to go low on trigger. When they are connected as expected the problem appears. Putting a meter on the line I see the voltage at about 2 volt on the COR line Then on key up there is a very brief drop like a pulse in voltage before coming back up to the 2 volts. It should stay low as long as its being keyed. Any ideas on a MOSFET isolation circuit? Any ideas would be much appreciated. Thanks in advance, WRYL353

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I have two RT97S repeaters that I've (unsuccessfully) attempted to attach a controller to. My experience is the exact same as yours with white noise being transmitted by the repeater whenever the control board keys the repeater. I was trying the ICS Basic and Linker IIA controllers.

I tried:

  • Putting a reed relay to key the repeater
  • Running the repeater and the controller off of different power supplies
  • Isolating the repeater's COR from the controller with a transistor switch
  • Isolating the repeater's COR from the controller with a diode
  • Isolating the repeater's COR from the controller with an optoisolator
  • Disconnecting the receive audio from the controller
  • Various combinations of everything above and probably some other things I'm not recalling at the moment

I had to move on to some other projects, but plan to getting back to trying. I'd bought a pair of the ID-O-Matics, thinking that maybe the issue was with the ICS' transmit audio interface circuit (both models of controllers have similar circuits). From your post, it's probably not the issue though.

One possible solution that I didn't try (yet) was coupling the audio through transformers. Combined with optoisolators/reed relays, that might totally isolate the repeater from the controller.

It's possible that the white noise that is transmitted when connected to the controller is actually the unsquelched receive audio. I've tried changing the squelch level as well as running ctcss, but it makes no difference. If it is the receive audio, that may be a show stopper since there don't appear to be any schematics available.

I didn't have access to my service monitor when I was trying to interface the controllers, but an interesting test would be to generate a signal with a 1KHz tone on the repeater input and see if you hear the tone instead of white noise.

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