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Repeater HELP!!!!

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WQOC472

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USA
Hello. I have a motorola GR1225 UHF Repeater. I recently purchased it as well as some LMR-400 coax and a Omni-Directional antenna. The repeater is running 30 watts on GMRS 462.550/467.550 (114.8pl)

I have had the repeater up for about 2 days now, and it has worked great. Until tonight when I went to transmit on it and when I released the PTT I got static (like someone had an open mic) which I know no one did... and ever so often it would make the "doubling" noise, (like 2 were trying to TX at the same time) which again, I know wasn't the case.

Also, the repeater does the CWID every 15mins and when the repeater ID's it self it works just fine... it has no static. Until I transmit on it then I release the PTT and again I get the "open air sound" from the repeater. Once I shut off the repeater and turn it back on then its fine until I TX on it again.

The antenna is about 50 feet from some powerlines and is elevated about 30 feet off the ground.

The antenna can be moved.

What should I do?

Thanks!
 

RRSINC

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47
Location
Woburn, MA
You say it sounds like an open mic after you TX, Could it be the repeater tail is just sent long... does the open mic sound eventually turn off?

Are you near any other repeaters that are on the same Freq that you could be hitting both at the same time?
 

mm

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Messages
610
It sounds like a classic example of passive intermod and/or desense holding the receiver open,

Your repeater controller may only enable the transmitter during ID periods with the receiver being ignored, some controllers can be set up this way.

If this happens then the repeater transmitter is not getting into the receiver during ID periods because the receiver isn't listening; however when you transmit during a period where the repeater isn't ID'ing the repeater transmitter is getting back in to the receiver which is enabled which brings us to the real problem.

Also check and see if your transmitter is sending out the same CTCSS tone as the receiver requires to access the repeater, if it is then you can change the transmit CTCSS tone and this should stop the transmitter from getting into the receiver and holding the squelch open but this will not fix the real problem.

Did you have your duplexer tuned after installing, sealing and tightening every connector ?

The big problem that I see is the LMR coax is not suitable as a repeater coax, due to the fact that LMR uses an outer weaved braid with a over coating consisting of aluminum over the braid which scrapes against one another creating PIM, the result is that the noise floor when using LMR coax is typically much higher when the repeater is active.

You really need some good quality hard line coax and then you need to tune the duplexer on site with everything connected and all connectors tight and sealed from the weather.

Mike
 

radioman2001

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Sounds like some desense, LMR is not recommended for the reasons posted. You also could have a loose connector, bad connector, water in the antenna or coax. If you have a dummy load, hook it up instead of the antenna and see if the problem goes away. Try disconnecting the RX from the duplexer and try that. Try and eliminate what portion of you system is causing this noise you describe,
 
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Concur; sounds like the duplexer tuning is off keeping the receiver open. LMR400 is not suitable for duplex use for that very reason. If you are going to install a repeater, you need to not go cheap on the antenna or feedline.
 

WQOC472

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Messages
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Location
USA
I tried it again this morning and it seems to be working good now. The guy i purchased it from programmed it backwards, i asked for the traditional RX:462.550 TX:467.550, But he programmed the opposite. I have purchased the programming software for the repeater and it should be here monday.

Here is the Link to the antenna i purchased

Tram/Browning BR-6155 [Tram/Browning BR-6155] - $79.95 : The Antenna Farm :: , Your Two Way Radio Source!

Here is the link to the coax

Times Mic LMR-400 [LMR-400] - $0.85 : The Antenna Farm :: , Your Two Way Radio Source!

I am running 65 feet of coax from the antenna mast to a climate controlled closet.

Any suggestions or help would be greatly appreicated!

Thanks!
 

ecps92

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Jul 8, 2002
Messages
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Location
Taxachusetts
Sounds like he programmed it Correctly. :wink:

Remember the Repeater is reverse of your Portable.

A Repeater would TX on 462 and Listen on 467
A Portable/Mobile would TX on 467 and Listen on 462

I tried it again this morning and it seems to be working good now. The guy i purchased it from programmed it backwards, i asked for the traditional RX:462.550 TX:467.550, But he programmed the opposite. I have purchased the programming software for the repeater and it should be here monday.

Here is the Link to the antenna i purchased

Tram/Browning BR-6155 [Tram/Browning BR-6155] - $79.95 : The Antenna Farm :: , Your Two Way Radio Source!

Here is the link to the coax

Times Mic LMR-400 [LMR-400] - $0.85 : The Antenna Farm :: , Your Two Way Radio Source!

I am running 65 feet of coax from the antenna mast to a climate controlled closet.

Any suggestions or help would be greatly appreicated!

Thanks!
 

MTS2000des

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Messages
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Location
Cobb County, GA Stadium Crime Zone
LMR400 is crap for repeater use. you'll eventually have noise, desense and other problems will eventually arise.

You lose about 1.7db of signal at 462MHz with LMR400 for your 65 foot run, if your repeater is putting out 30 watts into your duplexers, depending on the type of duplexer and their tuning, you can say you're getting around 17-22 watts out of the can. Up the feedline subtract 1.7db that leaves you with around 13 watts. Quite a bit of loss for a short run of cabling. Not to mention the noise problems on RX you'll get from desense.
 

n5ims

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Messages
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I concur on the coax. LMR-400 (or the larger 600, etc.) is good for receive only, transmit only, or normal two-way operation, but shouldn't be used in a duplex operation due to known issues with PIM.

Go with some quality coax like Andrew LDF4-50 (like Andrew LDF4-50A Heliax Coax Cable) which should work well, both for the passive intermod issue and lower loss. Use quality connectors and be sure that they're on correctly since bad or incorrectly installed connectors are also a major source of PIM.

If you must use LMR coax, get the new stuff that is designed to correct the PIM issues (http://www.timesmicrowave.com/downloads/products/lmr-sw.pdf) or the older TCOM type (http://www.timesmicrowave.com/products/lmr/downloads/126-129.pdf).
 

WQOC472

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USA
On the Hard line... Should i go with 1/4, 3/8, or 1/2??

the difference in price between the 1/4 and 1/2 is 99. a foot.

i will need 65 feet of coax
 

n5ims

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Messages
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On the Hard line... Should i go with 1/4, 3/8, or 1/2??

the difference in price between the 1/4 and 1/2 is 99. a foot.

i will need 65 feet of coax
That's nearly retail price, but you can easily find it for much less since tower folks buy it by the reel and sell off the ends for minimal cost. This one is nearly a buck a foot and almost the right size for your needs as well Andrew LDF4-50A 70' 1/2" Heliax Coaxial Cable New!!! | eBay
 

cmdrwill

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3,235
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So Cali
Neither one of the antennas are very good for duplex/repeater operation.

Also the LMR cable is know for desense problems in repeater operation.

Get your self some good hard line and a 'real' antenna.
 

n5ims

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Messages
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"Real Antenna"? Give me some suggestions on a "real" antenna.
Don't worry too much about the "Real Antenna" comment. While what you posted is an amateur or light duty commercial antenna, your repeater isn't a "100% gotta run perfect or folks might die" operation. If it was than that wouldn't be appropriate. For that type of operation you'd need a very high dollar DB Products Dipole Array antennas like these Decibel Products Antenna Drawings DB-404 DB-408 and DB-411. I won't tell you the price but you can see from this Andrew Solutions DB408 Dipole Base Antenna they ain't given 'em away.

It sounds like your main issue is PIM along with desense in the receiver. Since your coax is one well known to cause PIM that should be the first thing to address, which it sounds like you're doing. Since that would put you at the antenna anyway, if you were thinking about upgrading that anyway, now would be a great time to do so.

Once you make all of your changes, it would be a good idea to retune your duplexer (this'll require some good test equipment so it may pay to have someone come out to do it for you). This should make sure that everything is properly matched and isolated to eliminate the last bit of desense along with other issues you may not have yet found.
 

jackj

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Location
NW Ohio
Unless you have a good spectrum analyzer, stable marker generator and know what you're doing, LEAVE THE DUPLEXER ALONE!!
 

dmaria

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May 24, 2010
Messages
245
I hope you get the issues resolved, and it would be interesting to hear the resolution. I would like to see a GMRS repeater in this area and I'm sure others will apreciate your hard work.

Dave
K9DPM
WQNR758
 

n2hbx

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Messages
277
Location
Orlando, FL
If you're using the internal duplexer that comes with the 1225, it's a piece of junk. As soon as you can, replace it with a good pass-reject external duplexer.

Larry
 

wb0qqk

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Location
Omaha, Nebraska
A number of years ago, a GE Mastr II UHF repeater I installed had a similar problem. The only
way it would work was if the transmitter output was turned down below seven watts. The repeater
was connected to vertically spaced antennas through TX RX combiners. After days of researching
the problem, it was discovered that the Belden 9913 jumpers to the combiners had Radio Shack
'N' connectors on the ends that were radiating due to poor conductivity. They were cut off and
replaced with silver-clad Amphenol connectors and the problem went away.
 

radioman2001

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New York North Carolina and all points in between
The internal duplexer is good for most applications, if you are at a commercial site with a lot of high power transmitters I would agree that you would need to replace it. The easiest test is to get a 50 ohm dummy load, place it on the antenna port of the duplexer. If the problem goes away, then you know it's not the duplexer or radio. Then move the dummy load to the end of your coax, do the same tests, move the coax around see if it generates the noise you are complaining about, if so now you know it's the cable or it's connectors, if not start looking at the antenna, look at the connector, look at the weep holes in the antenna, make sure they are clear. Hook up the antenna and shake it, see if that generates the noise. Your problem isn't that hard to fix, it's finding where the noise is coming from. Don't replace anything until you do these simple tests.
 
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