Building a repeater with 2 maratracs.

[defcon-3]

Hello all,

I have 2 100 Watt motorola VHf maratracs lying around, and had a few questions about building a in-band repeater with them. First, how much frequency seperation do you need to get away without using a duplexer? This will be a vehicle install, so I can't seperate the antennas a huge amount. Also, on the maratrac, if you solder a connection inside, you can get a COS on the option connector. I am pretty new to these radio terms, so bear with me. Is it possible to go straight across, Radio 1 COS to Radio 2 PTT, and Radio 2 COS to Radio 1 PTT? And the same with the audio, can I take audio out from R1 to mic in on R2, and vice versa, or do I need a repeater controller? That seems too easy, but again, I am new to this.

Thanks a lot!

dc3

[RESCUE161]

100 watts? Ain't gonna happen without a duplexer, end of story.

I don't know how low you can drop the TX power, but the radio may flake out if you drop it too far.

I'd still imagine at even lower output that you'd still need to seperate the antennas more than a vehicle length.

[tvsjr]

This is closer to an infrastructure question, but...

1. You may as well forget about 100 watts. You're going to *have* to run a duplexer - it would take huge amounts of horizontal separation to make a repeater fly eithout a duplexer (you might be able to do it with vertical separation... but you probably don't have a chunk of tower bolted to your vehicle.) Unless you fancy carrying a 6-can BpBr duplexer around in your trunk, you're stuck with a mobile duplexer. That means 50 watts or less and at least 3-5MHz of spacing between input and output. Hambone 600Khz spacing? No way.

I believe the COS-PTT/vice-versa you're looking at is essentially what a RICK does. There are people far more knowledgeable around on this, however.

Most Motorola high-power PAs don't like dropping power too much. For example, 110-watt X9000 PAs start getting pissy around 60-70 watts. If you don't have a real spectrum analyzer to look at the output, you probably shouldn't be attempting this procedure.

Provided you have the separation to make a mobile duplexor work, perhaps you should consider trading the Maratracs for something like a Maxtrac/GM300. That would get you a much smaller package, easier interface, and a PA that won't flake on you.

[kb0nly]

All other subjects aside, let me answer the interface issue.

The Maratrac is basically a Maxtrac with a 100w PA on it. The logic board in the ones i have worked on are your run of the mill 5pin Maxtrac board. And its easy to get Cor/Cos and the other signals needed from the radio.

You can just solder to the pins on the front edge of the logic board for all the signals you need for repeater use, i'm talking about the pin headers where the connectors with all the wires come off, this is the same as where the front panel on a Maxtrac would connect.

I remember at one time someone suggested putting in a 16pin Maxtrac logic board, yes, you can do that, however the Maratrac RSS doesn't have the options for the accessory connector assignments. You could also make a frankenstein of sorts like i recently helped do. Its two Maratrac drawers with Maxtrac controls heads mounted to the top cover and they have 16 pin logic boards with Maxtrac firmware installed. This makes a 100w 32ch Maxtrac essentially, and can be programmed with Maxtrac RSS and also programmed for the 16pin accessory functions for repeater use.

That and you don't have to use the Maratrac control head and control cable, though you do still have to connect power to the front drawer connector, but i did that with a couple leftover Mitrek cable ends.

[kf4sqb]

As stated earlier, 100 watts in-band without a duplexer in a mobile ain't happening. Also, if you turn the output power down much more than app. 50%, it will start generating horrible spurs, and make you very unpopular with any other radio users in the area.


As for the interface, I wouldn't hook the output audio directly to the mic input. I would run it through a coupling capacitor. If you want, I will e-mail a diagram for doing what you are talking about doing on the Maxtrac/GM300/M1225, etc. mobiles. As Scott said, they use essentially the same logic board (well, except for the 1225, of course!), and have the "same" accessory connector.