GR500 Repeater Linking

[bcoray]

I just picked up a GR500 UHF repeater for cheap.

It has the R1225 transciever and a ZR310 Community Controller. I would like to set it up to link with another UHF repeater in an adjacent town. Can anyone offer suggestions on how best to do this?

Thanks!
Ben
WQJF348
West Jordan, Utah
[email protected]

[Doug]

Unfortunately the best way is not the cheapest way. If this is something that is to be used on a continuous bases I would invest in a quality repeater controller that has full support for a second transmitter. In doing so your keeping yourself legal with your id's and the time intervals for those id's. Also they give you a lot of options for adjusting your audio levels and controlling your link via dtmf options.
Your interfacing signals can be obtained on the rear accessory connector of your R1225 and other motorola radios with the 16 pin accessory connector. You can do a search on the board and find out your appropriate pins.
Another thing to remember is that heat is your worst enemy. Your going to be dealing with equipment that does not have high duty cycles so make sure you've got provisions for plenty of cooling.
I'm going to give you a couple of links. Pour yourself your favorite beverage and sit back and enjoy your reading
http://www.batlabs.com/
And also don't forget
http://www.repeater-builder.com/rbtip/
You can tie the two together with a simple cable but I don't think you'll enjoy your results.
Doug

[motorola_otaku]

Based on his posting a GMRS callsign, I'm pretty sure that's what he intends to use it for (i.e. non-critical.)

Before you can even get into connecting your R1225/ZR310 combo to a link radio, you need to deal with the RF side of things. First and foremost, your link radio is going to be listening for a signal on 462.xxx at the same time that your repeater is transmitting a signal on 462.xxx. This will cause desense of the link radio's RX, which is going to be very difficult to remediate with only a couple hundred kHz separation between frequencies (also, if, say, your repeater and the one you're trying to listen to are on adjacent pairs, then forget it.. it ain't happening.) Also, depending on what type of duplexer you're running on the R1225, you may also end up desensing the repeater's RX on 467.xxx with the link radio's TX.

Here is the only way I have seen it work: a GMRS repeater was put on the roof of a hi-rise building with its antenna about 10 feet above the elevator shack (which was located in the center of the roof about 75 feet from the roofline), and the link radio used a 10-element Yagi and was located on the side of the building about 10 feet down from the roofline. It also had its TX power turned down to 200 mW. It worked, but not particularly great.

So yeah, if you think you can manage a set-up like that, then you can get into the radio linking part.

[Doug]

It never dawned on me the frequency separation. Good catch! I've done several configurations like he is attempting only the ones I've done were in the hammy bands with 2 and 3 meg separation
Doug

[bcoray]

Thanks for the replies.

Here is my understanding, tell me if I am way off base.

I figured that if repeater A is listening for a 467.xxx RX and Link Radio A is also listening for RX but on 462.XXX there wouldn't be a conflict.

However, when Link A hears TX from Link B on 462.xxx it then trips Repeater A which also transmits on 462.xxx which from what your are telling me will cause a problem.

I thought about setting the RX for the link radios in the 467.xxx repeater input range but then that would cause a problem when a mobile radio trips Repeater A on 467.xxx then Link Radio A starts transmitting on 467.xxx and interfers with the input to Repeater A.

Looks like I'm hosed. I can't get enough separation between repeater freqs and link freqs with GMRS. How much separation is needed before desense is manageable? I may have access to some other UHF freqs with permission from a local shop here in town.

Thanks for your input, you have both been very helpful to a novice.

Ben

[Doug]

First of all let me apologize as my explanations are pretty rough. The problem is going to be when the repeater is keyed up on lets say 462.xxx your link receiver will be listening on 462.x25 or what ever the spacing is and you are going to create an over load on the link receiver port causing desense. This works in reverse as well. Say the link happens hear something on repeater "B" that will in turn key up repeater "A" causing it to transmit and then in turn cause the over load or desense problem all over again.
I realize that you are going to be running duplexers on the repeater and most likely so sort of filtering on your link but I've never run into set of filters with the skirting as tight as what your going to need. So your only solution is going to be antenna separation. My explanations are rough and I hope you get the idea.
Doug