Batboard

Hey guys,

I've been trying to get on the up and up about COR/COS to build a repeater project. Now I understand that Motorola COR is usually or can be programmed for active low. This can be interfaced to a PTT input to key up another receiver.

Now the problem. Through my research I see some other COR/COS outputs are possibly active high. This would mean they go positive when the radio receives. However PTT inputs seem to be always ground inputs (grounding the pin keys the radio).

Is this information generally correct? It seems that there is no standard for what is coming out of a COR/COS line.

Thanks!

You are absolutely right.
There is no standard.
And some receivers won't "sink" enough current to key some transmitters.
It is also common on some receivers that if you load that COS / COR / RUS circuit it won't work properly.
You kind of have to find out the needs of the RX, TX and controller you are going to use.

If you think about it even farther, unless a manufacturer is complying to an accepted standard for ANYTHING, there is no single accepted standard for ANY single component, IO gateway, or device. If a manufacturer puts a DB-9 componenent connector on the back of a device, unless the manufacturer states that it specifically complies with RS-232 standards, there is absolutely NO guarentee that you will get anything resembling RS-232 compliant levels, voltages and line assignments on the pins.
Manufacturers can put anything they want, anywhere they want. If they are particularly inclined, they can make it nonstandard and then make people buy parts from them, rather than generic equivalents. Sound fa/\/\iliar to anyone?

So it's pretty much hit or miss with that stuff...wonderful.

How about using a 5v reed relay to invert the polarity (to use an active high COR to key active low PTT)? I would imagine as long as there's enough power to trigger the relay this could also help for situations when the voltage change is not enough.

Could SW B+ be used as a 5V power source at the connector (in general, not for keying PTT)? I never really understood the function of it. I believe the max load is usually around 200ma, which is enough considering the max for most 5v PCB reed relays is 500ma.

I also see that some radios put out about 5v on the speaker leads, and that this can be used for COR. This concerns me. I can see hooking one lead up to a relay and turning on the radio just to hear the audio amp go pffft...

Thanks for all your help.

Of course you could use a small relay.
Anymore it is probably easier to use a cheap transistor. (2n2222, 2n3904 etc)
A good example of a COS inverter is posted on the NHRC controller website.
Look for "COS inverter" or something similar on their site, and you should find it.
Using the audio output on a radio is not a very good way, and in most cases won't work.
Relays work, but anymore its usually cheaper to use transistors.
Then again, I will often use whatever is handy in the supplies I have.

Yeah I thought about the transistor too. That probably would be easier. Too bad I already bought the reed relays. Thanks for the links to the circuit. I chose a reed relay for the switching time. I was concerned that a standard solid state relay wouldn't switch fast enough in times of rapid opening/closing of squelch.

Oh well.

Thanks guys.