Batboard

I'm a Communications Officer for the USMC,
I going to be given a GR500 and told to make it work tomorrow. Any help that can be given to me will be greatly appreciated. This radio repeater will help extend the range at which the Iraqi Police can go on patrols without losing comm.

Some of these questions might seem simple, but I'm not familiar with motorola radio systems at all.

- The repeater has two different radios. Should the repeater receive and transmit the same signal? If not, why is simplex not desirable?

- How does the duplex work? If a radio's transmit and receive frequencies are different, and another radio is programmed identically, isn't the other radio waiting to receive at the wrong frequency?
Example, two radios programmed the same:
Radio 1
TX1 = 140.00
RX1 = 141.00

Radio 2
TX1 = 140.00
RX1 = 141.00

Radio 1 -> Radio 2
140.00 /= 141.00 ???

-Should the repeater be set on the same frequencies as the radios?
Repeater
TX = 140.00
RX = 141.00

-Does anyone have a manual or words of wisdom to pass?

Thanks,
V/R/S,
CommO

I see from your IP's that you are who you probably say that you are -

I'm going to give you some advice, take it or leave it - I wouldn't go posting potential frequencies, or other hypothetical information here, and while we can help you with your questions, anyone on the internet can read this board.

With this in mind.

The GR is going to have 2 radios in it, and then it's going to have a repeater controler. One radio is programmed for rx, the other for tx. The portable or mobile radios ment to talk through this repeater, must be setup to rx on the tx radios frequency, and tx on the rx frequency of the repeater. (where TX=Transmit and RX=Receive)

The Repeater controler is responsible for doing things such as repeater hang time, identifying itself, and controling when to turn the fans on, and other such things to ensure that everything is functioning as planned.

So really, here's what your going to need.

If the radios require reprogramming, your going to probably need GM300 RSS in order to reprogram the two radios. The radios could also be M1225's, or other pieces of hardware, I'm not sure what radios come in a GR500 off hand. Your going to also need RSS to program the actual controler, I haven't programmed one, so I'm not sure what specific package you'll need.

From there, you'll need the portable specific software in order to program the portables, or mobiles (if they are different from what is in the case).

As it stands, you'll also need the appropriate RIB (Radio Interface Box), Laptop (go to http://www.batlabs.com and read the primer on programming for what is a good system to use), and power to power both the rib and laptop during programming.

So going back to your illustration using the frequencies listed:

The transmit in the repeater should be: 141.00
The receive in the repeater should be 140.00

The portables:

TX: 140.00
RX: 141.00

I would put a DPL on the repeater.

Keep in mind, this operates in the clear, so anyone can listen. If you guys are expecting this stuff to be secure - you really have another thing coming.

You also will need to use 2 antenna's, one for RX, and 1 for TX. Keep in mind you'll need to properly ground and space these in order to gain maximum efficeny, and have the repeater work correctly. It is best to use a duplexer if one is avaliable, but it will have to be tuned to your frequency, you can't just pull one off the shelf.

-Alex

Sir,
Thanks for the information. We have all the equipment to make it work.

I just didn't understand how it worked.
Those example frequencies were just that.
We have our own radios for secure communications.
The Iraqi Police force communicates in similar ways to ours.

I have a few more questions.
-What is a DPL?
-What spacing requirements are there for the antennas?

V/R/S,
CommO

Send me an e-mail ([email protected]) marine and will se about getting you set up to go through the repeater with no trouble.

DB

DPL = Digital PL, keeps unwanted signal from opening the receiver on the radio.

Antenna spacing depends on the frequency...UHF or VHF??

And If you call me Sir, I will have get my stripes out.

DB

A couple of thoughts:

One question asked was "Why repeat?" The fundamental reason for repeating is to extend the effective range between two field units. These field units can talk even though they are beyond the range for simplex communications, so long as each is within range of the repeater transmitter and a receiver, which are usually located in strategic high sites.

A second reason for repeating is that by splitting the input and output traffic, a field unit in trouble can transmit and be heard even while the dispatcher is transmitting directly over the output frequency.

The downside to repeating is that there can be situations where two units are close enough for simplex but one or both cannot hit the repeater. This is why you either have to program a "direct" button or program the "direct" channel in the radio -- and train the troops on its use.

It sounds like a lot of this is new to you, so let me offer a suggestion: instead of thinking of frequencies in MHz, think of repeater pairs as having an "Input" frequency and an "Output" frequency. The "input" is what field units transmit on when using the repeater. The Output is what the repeater's transmitter transmits on (its receiver listens on the input frequency, unless it has an auxiliary receiver, in which case it listens on both frequencies so long as the transmitter is not active). The Output is also what field units transmit on when on "direct." Note that for both the "repeat" and "direct" channels, the field units are listening to the same frequency, the Output. This enables a Unit A to hail Unit B on direct even though Unit B's radio is set for "repeat."

Then all you have to remember when programming radios is:

Portables Xmit on Input and Rx on Output.
Bases Xmit on Output and Rx on Input.

My two bits worth:
By all means use a duplexer if one is available, otherwise use two antennas.
The antennas must be vertically spaced exactly in line.

The further apart the channels are the better.
A duplexer for 600KC seperation is about the size of a file cabinet.
You could hold a 5 MHZ seperation duplexer in the palm of your hand.

600 KC seperation would require 50' vertical spacing or quarter mile horozontal seperation.

5 MHZ seperation works with very little vertical spacing.

The problem is that if there is not enough isolation between your receiver and your and other transmitters you have "Receiver Desense".

With the repeater disabled receive a weak signal with an Iso tee and signal generator, or from a unit in the field in a bad location, enable the repeater function, observe the quality of the received signal on the local speaker.
If there is no change, all is well, if it gets very noisy, or squelches you have a problem.
In this case inspect all cables and connectors, seperate the antennas, retune the duplexer, find another frequency pair.

Also, and I mean this advice with all seriousnes, put out whatever your unit uses for inter unit bulletins for a radio amateur or other tech with vhf/uhf experience.

ESPECIALLY if you are using separate antennas, you need good quality coax, to prevent the repeater transmit signal from "desensitizing" (desense) the repeater receiver. Leaky, poorly shielded coax with guarantee that problem.


Also, be aware that wider freq separation between tx and rx will help the desense problem, especially with using two antennas.

I think they are asking a lot of you for your level of expertise, I second the recomendation to try to find the Ham radio operator hiding in your ranks. It would probably be a welcome distraction for him or her as well as very helpful to you.