Batboard

Hi gang. I'm putting together the 1-way repeater as found on Nand's site. Basically, I want to take audio and COR from a Low Band Maxtrac (which has the 16 pin connector), and have it repeated out onto a UHF frequency, using a 5 pin UHF Maxtrac.

I was going to modify the circuit slightly. How would the following work:

1) Tie grounds together through pin 7 on the Low Band, and the mic jack on the UHF.
2) Tie the RX Audio (Pin 11) on the Low Band, to the Mic Input on the mic jack of the UHF.
3) Tie the COR on the Low Band to the PTT line on the UHF's mic jack.

If I didn't build it with the audio level components that Nand suggests, am I risking any damage? I would really like to make this as simple as possible.

The other option, which I'm thinking might work better. Modify the Mic Jack on the Low Band to provide COR on an unused pin in the mic jack. Then, just make a cable with two RJ45 connectors on either end, one for the RX and one for the TX.

In theory this should work, I just wanted to check before I start hacking!

Also, forgot to mention. Should I bother using a transistor to pull the PTT line to ground, or is it safe to connect it directly to a COS pin that's set to "Active Low"?

There is a major problem in using these radios in this fashion.

1. They are not designed for high TX duty. The TX
is only rated for about 10% TX at the most.

2. You need some control to time out the connection.
Setting the time out timer on the TX side is a start.

3. You will need some way of setting the audio level going
from the RX to the TX.

4. You need to have some form of ID on the TX side every
xx minutes depending on the service they are used in.

5. Your frequemcies need to have the license modified to
allow repeater service. Not all services are allowed
to run a repeater.

Jim

I have made a crude repeater "interface", if you can call it that, using only two 10uF capacitors and a pair of RJ45 plugs.

You can make your own COR using one 4.7k resistor and one common NPN silicon transistor (2N2222 for example) by tapping the RX MUTE signal on the logic board and bringing it out to the MIC jack pin 1. Lots of people do this; see the MaxTrac Interfacing article on http://www.repeater-builder.com in the Motorola area. It'll work on VHF, UHF, and 800 MHz radios; the 900 MHz radios do not have wiring to get to pin 1 on the MIC jack. Do this on both radios. The PTT requirements are minimal and the transistor will easily pull PTT to ground.

The COR output signal goes directly to the other radio's PTT input.

The headset audio output signal goes through a capacitor to the other radio's MIC audio input.

Ground goes to ground plus the hang-up terminal on each radio. This enables PL/DPL decoding. If you want to make it carrier squelch, either press the MON button on the radio or don't ground the hang-up terminal.

It's not perfect; the audio probably will be too loud, so a resistor in series with the capacitor would allow it to be suitably adjusted. You only need one capacitor for each MIC input (the positive terminal goes to the MIC input) so if the repeater is only going to be uni-directional, you only need one capacitor.

Of course, there's no CW ID or timers, but for a quick test on the bench, something you can throw together in a couple of minutes, it's not bad. Plus, after you add COR to the radios, you can do everything you need from the front panels.

Bob M.

Okay.. well.

Firstly, the TX duty cycle MIGHT be 1%. That is, it'll be transmitting maybe a minute out of an hour's time.

It's for the Amateur service, so I'm not too worried about the license issue.

Basically, there's a UHF ham repeater that also has a 6m side. I can HIT the UHF side perfect, I just can't hear it. So, I'll transmit out the lowband on a UHF simplex channel, but transmit out on the portable on the actual input channel.

bellersley wrote:Okay.. well.

Firstly, the TX duty cycle MIGHT be 1%. That is, it'll be transmitting maybe a minute out of an hour's time.

It's for the Amateur service, so I'm not too worried about the license issue.

Basically, there's a UHF ham repeater that also has a 6m side. I can HIT the UHF side perfect, I just can't hear it. So, I'll transmit out the lowband on a UHF simplex channel, but transmit out on the portable on the actual input channel.

Legally you have to ID that UHF transmitter every 10m, but in practice I doubt you will get much flack.

Legally, I can't use encryption on the ham bands either.

But yea. As I said, this would be getting VERY little use. It's a specific purpose-built repeater for a trip I'm doing in the middle of nowhere. Cellphones don't work. Anything short of 100 watts on lowband isn't going to get heard by a single person, exception is this UHF ham repeater that's very nearby.

You should follow Nand's diagram. YES you do need the audio adjustment pot. You can use the Mic jack on the transmit radio for connection.