Repeater Control Schematic.. UPDATED!

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sun Aug 10, 2003 8:04 pm

See new schematic at bottom of post
------------------------------------------------

It's the control circuitry for a MaxTrac repeater.

It is based around the Midian ID-1 CW-ID'er / simple controller.

http://personal.cmich.edu/~weirm1js/900_4.gif

I tried to be as neat as I could.

Thank you.

Will · Post by **Will** » Sun Aug 10, 2003 9:48 pm

Jonathan, for what you are doing you do not need the opto isolator chips. BUT if one radio has a problem it will key up the other radio's transmitter till the cows come back home.
The opto isolator chips accually draw way too much from the COS/TOS line and load it way dow.

perthcom · Post by **perthcom** » Mon Aug 11, 2003 4:23 am

Hi
At first glance, my observations:
- You are using Pin 4 for your COS control (13V out on Rx), but there is no current limit resistor for your Opto_isolator input. Use about 680ohm resistor here.

- You are paralleling 3 audios into one low impedance input. I think you might run into muffled Tx audio here. Buffering with an OpAmp will fix this.

Be sure to bond all the cases together to ground.

Its not the way I do it, but it should work.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Mon Aug 11, 2003 9:42 pm

Rather then two optoisolators.. could I use a NOR gate instead?

Will · Post by **Will** » Tue Aug 12, 2003 1:59 am

"You are using Pin 4 for your COS control (13V out on Rx)," no use pin 8 for the zero true output to key the transmitter. I'll double check the roadmap as it was too big for my screen.

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Mon Aug 25, 2003 11:24 am

I updated this.

http://personal.cmich.edu/~weirm1js/REPEATER.gif

I picked up a free Student Version of CircuitWorks, so you will find it is a lot easier to look at then my messy schematics.

The audio mixer was taken from a design by Forrest M. Mimms, III. Another part of the audio section was taken from Nand's design.

It now uses pin 8 for CSQ+PL, rather then pin 4. That means it uses TTL levels now. It is set for logic high on active, so that the transmitter cannot be locked up when one of the recievers goes dead, like what happens in other designs I have seen.

I still need to work on powering the OpAmp, and the NOR gate.

The pinouts/config of the Rx MaxTracs are:
7 - Ground
8 - CSQ+PL, active high [+5V]
11 - Audio

The pinouts/config of the Tx MaxTrac are:
2 - Mic Audio In
3- PTT
7 - Ground

The pinouts/config of the Midian ID-1 are:
Black - Ground
Red - +12V
Brown - COS In (active low)
Green - CW output
Gray - PTT In (active low)
White - PTT Out (active low)

Again, feedback is welcome.

Nand · Post by **Nand** » Mon Aug 25, 2003 6:23 pm

For combining COR outputs (pin 8 ), I would just tie them together and program these for active low going into the Midian board. The COR outputs are not actively pulled high inside the Maxtrac so you won’t do any damage by tying them together; they are internally pulled up by a resistor.

But I you like to have the COR active high instead, you could just tie them together with each output in series with a small signaling diode like the 1N914, cathodes together on to the Midian board. The Midian board now needs to be programmed for active high COR input instead. This will satisfy Will’s observation about the possibility of the TX radio staying keyed if the RX radio looses power and the cows won’t come home. The time out timer in either the TX radio or the Midian board will bring the cows home as well.

As for the combining of the RX audio (pin 11), you may have experiment a bit. Perthcom pointed you in the right direction, but he has the equipment to confirm the results. In your case, I would likely start out by tying both pins 11 together and feed them in a single repeat level control and onwards to the mic circuit (pin 2). The ID audio is quit high and can go to the mic input through a series resistor that you may need to determine by trial and mistake. You can even try to input the ID audio into the flat TX audio (pin 5) instead though a large resistor (100K?)

I assume that you do not have any equipment to check the repeat audio deviation with. So you will have to compare the repeated audio level with the simplex level for both radios.

Nand.

Will · Post by **Will** » Tue Sep 02, 2003 1:52 am

I think the op-amp needs to be biased so the output is at half supply voltage.

Will · Post by **Will** » Tue Sep 02, 2003 1:56 am

Take the power for the circuit from the transmit Maxtrac and use a regulator chip for the correct VCC to the logic chip. You will need a series resistor on the ID audio output to bring the level down and to isolate the ID from the rest of the audio circuits and reduce noise pickup on the "flat" input.