RT97s to ID-O-Matic interface problem

[Moonlight]

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

[Moonlight]

I got away from solving the problem interfacing the ID-O-Matic with the RT97S to take care of immediate problems around the house. I determined that the COR out on the RT97S does indeed have audio on that line and will feed back into the COR in and modulate the radio given a chance. I was really disappointed with the engineering frankly. I conjured up this very simple circuit that I bread-boarded that solved the audio feed through problem. It's also a very cost effective solution and easy to build. The components can be obtained online or whatever you might have in the junk box. Only things I ordered was the LM44D00 two pole relay, some 2N2222's and green LEDs that gave be a visual feedback of operation. The LED and associated resistor can be eliminated if desired. The circuit works almost perfectly with one exception. When the ID-O-Matic activates and keys the radio you cannot key the repeater until the ID-O-Matic relinquishes the COR in line. This means during that short brief time during the courtesy beep the repeater cannot be keyed. This shouldn't be a problem in most cases since the beep duration is very short. And on air etiquette usually means a user pauses for a couple of seconds to allow another user to join the conversion. So not a real problem. This is true also when the unit is sending id. My unit ids in CW and voice. Takes just a few moments so it shouldn't be a real problem. But at least the horrible feed-through problem is fixed. I also put 16 pin DIP sockets on the board for the 4049 chip and the miniature relay. Hope you find this useful and if so and you hear of others with the same problem with this configuration feel free to share the circuit diagram to them. Best of luck with your project. WRLY353

 

[SteveShannon]

Is it possible that it just floats back up to 2 volts?  Would a simple 10k pull-down resistor to ground prevent it from floating?

[WRTM529]

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.

[WRZB793]

On 8/28/2023 at 10:12 PM, Moonlight said:

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

Have you resolved this issue? I'm pretty new to this and am / was interested in putting an ID O Matic on my RT97S. I know nothing about circuits, I guess that's why I am not a HAM. WRZB793