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Repeater Help! (Motorola GR1225 UHF)


Durake
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Hey! Doubtful I'll have an answer or suggestion by the time I leave tomorrow, but I was loaned a Motorola GR1225 UHF Repeater for an event I'm doing this weekend. Along with some LMR400 and an antenna. Essentially the full setup. Its a full 40 watt repeater with tuned duplexer.

 

But, the issue is, the range is so short! I'm only pushing 25 watts and this was just pulled from a working environment where it was actually pushing the full 40 and coverage was perfect. The only changes are the LMR, the one previously used was some high dollar 15 bucks a foot extremely low loss cable, and the antenna. Its a UHF J-Pole antenna, and I've already tried multiple types of things including changing the cable, and antenna, adjusting the programming a bit, and the range is just crazy short. I even had a friend stop by and try to trouble shoot it. I just don't understand. I can go without the repeater for this event for the most part, but I would appreciate a solution. 

 

I can't imagine what would be wrong with it, everything is screwed in correctly, fixed up, set right, I've triple checked! The range is only not even a block, the antenna is about 12 foot up in the air in a clear line of sight environment. Help!!

 

(I'll feel really stupid if its something like the push of a button, lol.)

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I don't have much experience with that repeater, maybe someone else can give they're thoughts if you can't get anything more. But, my only ideas are, have you tried different heights just to check and you tried adjusting the power? I believe each channel can be set to different powers. You're getting 25w on each channel?

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I don't have much experience with that repeater, maybe someone else can give they're thoughts if you can't get anything more. But, my only ideas are, have you tried different heights just to check and you tried adjusting the power? I believe each channel can be set to different powers. You're getting 25w on each channel?

 

Yeah, I also tried it at about.. 24 foot I'd say. It's surprisingly worse at that point. I can do 40 or 25 on each channel, I tried it with 40 and it makes little difference. 

Thanks for the quick reply.

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Yeah, that's odd. If you can measure out about 40w, but, getting little difference at about 24', I would say either obstructions or cable or antenna. But, you mentioned you tried different cable, antenna, and no obstructions. What was the range like before and mounting point? Sorry that I probably won't be any help. :(

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A couple of random thoughts:

 

1) LMR400 is prone to intermod when used between a duplexer and an antenna. Especially if the coax is not new.

 

2) Are you certain the duplexer was tuned for GMRS in general, and your specific frequency in particular?

 

3) As noted already by @ZAP, these radios are VERY prone to blowing/burning the final. Running at a high duty-cycle will almost certainly blow the final.   I would not run it any higher than 25w and they should really be run at as low an output as works for your needs.  It sounds like you may already have a problem. 

 

4) It seems you are testing with a field strength meter. Do you have a (good quality, like a Bird) meter and a dummy load you can use. That is the only way to get a reliable reading for the output.

 

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It's too late by several days, but were you using the same exact frequency pair that the duplexer is tuned for? If not, then that was the problem!

This describes exactly what your symptoms were. It doesn't take much to bump a mobile duplexer out of tune sometimes.

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This repeater was a backup GMRS Repeater for REACT. Only used a few times. I was using the frequency the duplexer was tuned to, and I think the PA blew, sounds like the issue. I'm taking it to get it checked out here soon. Thanks y'all for the help! I'll keep y'all updated on the status.

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A bad antenna and coax can cause headaches for GMRS (or UHF in general). I have multiple repeater at tower sites that have great coverage but are installed properly with 1/2" or 7/8" heliax and a real base station antenna. I have removed one of them for a temp repeater in the past doing similar to what you are doing. Never have i gotten decent coverage. LMR400 as others said is not the best for this. I have found 1/2" andrews superflex has been good for a temp setup. I run it on a 25' mast with a DB404 antenna and get decent coverage. 

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what ever fault blew your finals, If still present will just blow them again. Check every connector, every inch of feedline and have the duplexor hooked to a frequency counter to check it's status. As has already been said, slightest bump can change tunning and sensitivity.

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