GP Series DIY Repeater

[Nickinator]

Hi all,
I purchased a few GP328's on eBay a while ago, and I've just started learning about them and really getting into them, I'm a bit of an electronics tinkerer, and I'd like to build my own repeater. What I'm thinking here is as simple as it gets - two radios hooked up some distance apart via the 13 Pin Auxillary Connector's Speaker Pin going to the Mic Pin.
I've a few questions regarding this however, the first is:
What's the pinout on these? I've read different bits about what different pins do, and I've looked at all the publicly accessible Motorola documentation, but none seem to give me a concise answer as to the function of each of the pins, and what I'll have to do to get PTT to work or is that what the VOX function is for?
The second is: What's the Impedance / Voltage the Mic transmits and what's the Impedance / Voltage the Speaker transmits? - Are the two compatible or will I have to step down / amplify voltages?
I've heard of "Parot" repeaters that simply record something and re-transmit it back. What's the ballpark price on one of these, I'm sure I can build one using some inexpensive microcontrollers for about ~$20, but there's no point if such a product already exists for next to nothing, and any names / pointers I should search for for these?
I've heard that having a reciever and a transmitter functioning at the same time next to eachother can cause some kind of "tunnel" effect or something where the two signals partially cancell eachother out, for my WiFi at home I've got a directional antenna, is the same thing available for the 403-470Mhz specrum or is it something I can make myself?
Thanks for taking the time to read this rather gargantuan first post, but I'll be sticking around!
Cheers,
Nickinator

[Jim202]

Hi all,
I purchased a few GP328's on eBay a while ago, and I've just started learning about them and really getting into them, I'm a bit of an electronics tinkerer, and I'd like to build my own repeater. What I'm thinking here is as simple as it gets - two radios hooked up some distance apart via the 13 Pin Auxillary Connector's Speaker Pin going to the Mic Pin.
I've a few questions regarding this however, the first is:
What's the pinout on these? I've read different bits about what different pins do, and I've looked at all the publicly accessible Motorola documentation, but none seem to give me a concise answer as to the function of each of the pins, and what I'll have to do to get PTT to work or is that what the VOX function is for?
The second is: What's the Impedance / Voltage the Mic transmits and what's the Impedance / Voltage the Speaker transmits? - Are the two compatible or will I have to step down / amplify voltages?
I've heard of "Parot" repeaters that simply record something and re-transmit it back. What's the ballpark price on one of these, I'm sure I can build one using some inexpensive microcontrollers for about ~$20, but there's no point if such a product already exists for next to nothing, and any names / pointers I should search for for these?
I've heard that having a reciever and a transmitter functioning at the same time next to eachother can cause some kind of "tunnel" effect or something where the two signals partially cancell eachother out, for my WiFi at home I've got a directional antenna, is the same thing available for the 403-470Mhz specrum or is it something I can make myself?
Thanks for taking the time to read this rather gargantuan first post, but I'll be sticking around!
Cheers,
Nickinator

First of all don't go just connecting the speaker output of one radio to the mic input of a second radio. Your going to let the smoke out to start with. In most of the Motorola radios, the speaker output has voltage on both wires to ground. If you ground either of these wires you will blow the audio output circuit.

Second, the mic input on most of the Motorola radios has a DC bias on it. Grounding this bias out will cause a number of problems. You might cause circuit damage, you will cause transmit audio problems and you could even cause the transmitter to be slightly off frequency.

The speaker output levels are way too high to just jack it into another radio mic input. You will at a minimum, need some sort of level control.

In trying to create a repeater, you should use some sort of control circuit. This should contain audio level control, timers to limit the transmit duration and also contain some sort of station ID at least every 10 minutes of operation.

You should have some sort of filter on both the transmit output and receiver input. This is intended to limit the receiver from being clobbered by the transmitter being on at the same time. Most repeaters use a duplexer to perform this function and let you use only one antenna.

Go do some homework on building a repeater before going too far.

[Nickinator]

Thanks for your info,
I'll keep scouring the net see if I can find more info on the speaker output and mic inputs, if that fails I'll hook it up to my scope and see what it looks like. I'm thinking then I'll feed it into a Microcontroller that way I have the rules to limit transmit duration. What sort of station ID would you reccomend? A voice prompt saying "This is X repeater in X town?" I'm in Australia so everything's a little more "Free for all" than in the states in regards to radio laws.

[Bill_G]

Welcome Nick -

16 pin accy port - http://www.batlabs.com/images/maxacc.gif

As Jim mentioned, to hook two radios together to make a repeater, you need some kind of controller. There is a low cost one available for the model radio you own. Repeater interface kit (RICK) - http://www.batlabs.com/rick.html

A "parrot" repeater is also know as a "store and forward" or "simplex" repeater - http://www.midians.com/html/products.as ... +Repeaters

You will need software and programming cables - look for a Motorola dealer in your area.

You will need a duplexer - http://www.ebay.com/sch/i.html?_nkw=uhf+duplexer

You will need an antenna and coaxial cable - http://lairdtech.thomasnet.com/category ... nas&bc=100

It's a straight forward project, but it can easily be done wrong. Keep studying.

[Nickinator]

Welcome Nick -

16 pin accy port - http://www.batlabs.com/images/maxacc.gif

Thanks Bill, I've seen that diagram, but it's got 16 pins, mine has 13, as do most of the GP Series from what I've seen, I've ordered a programming cable and I've got a handpice for it, which will let me know what a lot of the ports do, I'll hook the handset up to a mutli-meter over the weekend see if I can find which two are the PTT, Speaker and Mic, shouldn't be too hard, and I've already ordered a Ribless programming cable from eBay, I've heard varied things about them, but we'll see how it goes.

Can you explain the need for a duplexer if I'm using two radios connected to eachother? Or would it just be so I can use a singular antenna, what was thinking of was a directional antenna for recieving and a non directional antenna for transmitting, it's just a geographic thing, I'm more likley to be wanting to transmit from a remote location than to transmit from anywhere the repeater's range is tuned too.

Are there simple Op Amps I can use to boost the 4w my radio is producing, in my head it would make sense, but do devices exist, are they simply op amps or are the infinatley more complex?

[Bill_G]

Doh! You have portables. I wouldn't even attempt to turn them into a repeater. You don't use a bicycle to pull a truck trailer. You know, I'm just sayin ...

Do some more reading Nick. There are a lot of discussions providing the background you need. This is a well traveled path.