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Mobile Extenders on GMRS Interstitial


ASRM
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While I am just getting back into GMRS, one idea I was toying around with was getting one of those Vertex mobile extenders and use the one of the GMRS interstitial frequencies as the extender frequencies (I wasn't aware these were for GMRS and could be at 5 watts)

 

Considering it would all be under the same radio group class, no cross linking like I saw mentioned people doing with MURS or Interrent Business freq's would this be allowed? I like the idea that if we are in decent mobile coverage but spotty or inside a building, having a nice solid 1 mile radius, heck even just 1/4 to 1/2 mile solid would be ideal as a decent communication plan for HT use, seems you can snag the Vertex units for $50 to $100 on eBay.

 

Thanks

 

Dave

 

ETA: grammar

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I wont get into a rules argument however have installed many of these mobile repeaters/extenders in vehicles over the years. The biggest issue you will have is with the VRM being decensed by the mobile radio. This is extremely difficult in "IN BAND" configurations such as uhf uhf. I have done many in cross band configuration and work very well. In UHF the issue i ran into was frequency separation. Using a mobile on 462/465 and the VRM on the 462 may get you enough seperation but i think you will still see poor performance. If your 20' from your car all is fine but if your inside a building with your car in the parking lot it will have issues. You also need to seperate your antenna as far as possible. The last system i did in band was a mobile on 453/458 and the VRM on 465. We still had issue on high power so switched to 800.

 

As for the VXR1000 its a solid little unit and is great for what you want to try. The nice thing about the vertex is the channel change. So in reality if you had someo ther channels outside the FRS band in your mobile and portable you could use it for both services, vs just locking it to one channel.

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I wont get into a rules argument however have installed many of these mobile repeaters/extenders in vehicles over the years. The biggest issue you will have is with the VRM being decensed by the mobile radio. This is extremely difficult in "IN BAND" configurations such as uhf uhf. I have done many in cross band configuration and work very well. In UHF the issue i ran into was frequency separation. Using a mobile on 462/465 and the VRM on the 462 may get you enough seperation but i think you will still see poor performance. If your 20' from your car all is fine but if your inside a building with your car in the parking lot it will have issues. You also need to seperate your antenna as far as possible. The last system i did in band was a mobile on 453/458 and the VRM on 465. We still had issue on high power so switched to 800.

 

As for the VXR1000 its a solid little unit and is great for what you want to try. The nice thing about the vertex is the channel change. So in reality if you had someo ther channels outside the FRS band in your mobile and portable you could use it for both services, vs just locking it to one channel.

 

Thanks for the insight, my thought was possibly having the mobile antenna on the front fender, and using a small whip of something inside the car (well SUV) or maybe inverted under the car, like I was saying, if I could get good coverage 1/4 to 1/2 mile solid, as I wouldn't see myself or wife ever further then that unless we were hiking somewhere, that could present an issue, but then I would hope I have planned ahead and scoped like minded GMRS repeaters to use.

 

Again excellent information as that was what I was after, pro's and con's though not sure if it was legally addressed. I would think a repeater is a repeater no matter the location? Noting in the rules state what is to be a repeater (or maybe it does now that I think this out).

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I have been successful in putting a BNC rubber buck in the back window of a car with a short cable to the VXR. It is out of sight and performs well. The VXR is only 4 watts anyway so it is just acting as a portable at this point. If you did a quarter wave on the center of the roof with this configuration and stay away from your mobile TX frequency you may be ok for what you are trying to do. I would limit your mobile to lowest power you can go and reliably get into the repeater. I use a CDM1250 and have low power at 10 watts. That will help your decense greatly. If money is not a factor using a tuned ceramic filter inline with the VXR is another way to clean up the signal but then you are limited to one channel only.

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Thank you, our mobiles are CDM1225's at 20 watts, nothing to say once I go this route I could program the mobile on a certain channel to be lower power when on the extender, I also thought of the HT antenna idea as well.

 

Thank you as this helps guide me in the future of setting up a unit, the wife will probably thumb it down as she used to have to use rigs like this all the time as a cop, I guess after 25+ years you don't find the fun in it like a civvy  :P

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I think the issue will be the receiver in the MRE verus anything else. If you can get the antennae as far apart as possible, and use as little power on the CDM as possible (If you don't have hi/lo programmed on it, get it set for 10 and 40 then you can switch it) and use 1/2 watt on the MRE you may get better results. 

 

I have done all sorts of projects in commercial/public safety and sometime you would be surprised what a better antenna position and LESS power will do. 

 

I know when we used to service PAC-RTs as MRE on Low Band MICOR radios...the VHF PAC-RT's ran at 250mw and the HT600's were 1 watt. Of course the Micor was low band, but it was blasting 100-120 watts on a long whip 2 1/2 feet from the VHF antenna.

 

In band is tough, not alot of options, but worth playing with. I had a case to (oops!) leave a 1/2 watt FRS on VOX laying in front of my Uniden 780 scanner in my truck and listening on my P1225 while out of the truck....worked great, even when the 780 was picking up 453 and the FRS was Txing 467. I could get 1/4 mile away in a building and still hear it. Didn't do that much, but had some stuff going on once that I wasn't going to miss...needed LB, VHF, UHF and 800 all together.   

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