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UHF Repeater HELP!!!

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WQOC472

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Hello all,

I have a cheapy UHF Repeater i bought off eBay, The repeater is a Motorola SM50 on TX inerfaced to a P110 on RX, its putting out about 30W, with a cellwave duplexer fed into LDF4-50A 1/2" Heilax, with a 5db Tram/Browning BR-6155 as the antenna.

Here is the issue:

I have a Kenwood TK-8180 30W mobile, as well as a Motorola Spectra 45W mobile, with identical High Gain antennas mounted in my vehicle. I also have a Kenwood TK-3180 handheld.

When i key up the repeater (less than 1 mile from the repeater location) on either of the Mobiles all i get is static, but when i key up with my 4W handheld from the same location, it sounds great with no static and good clean audio.

What is happening here? Are my mobiles bad? Or is the repeater just a piece of crap?

I am just using this repeater until my Vertex VXR-7000 comes in sometime next week.


Thanks again for the help,
 

SCPD

QRT
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Virginia
If you are keying the repeater with one mobile and listening on the other or on your hand-held, your high power mobile is desensing the receiver of the radio you are listening on.
 

WQOC472

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So in all reaility the mobiles are transmitting just fine? I was doing some tests by my self today, and wasn't able to test with anyone else from a good distance away.
 

Rob_K

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I am not an expert by any means but going with the above post, I would turn one of the mobiles off and test with your 3180 and the other mobile.
 

WQOC472

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How can i overcome this? When i use the same radios on my local Police Dept, repeater, i key up on my mobile and i have my handheld on sitting in the car with my, it receives just fine.

How can i overcome this with my repeater?
 

SCPD

QRT
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Yes, the high power of the mobile is "killing" your receiver where as the 4 watt HT doesn't bother it so much.
 

WQOC472

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I am not an expert by any means but going with the above post, I would turn one of the mobiles off and test with your 3180 and the other mobile.
That is what i was doing, I had my 3180 receiving and i was transmitting with my 8180 and all i got was static, and likewise with the spectra and the 3180 as well with the same result.
 

SCPD

QRT
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I don't know what to tell you on how how to fix it. But the reason the you don't have the same problem on the PD repeater is probably because the have a much higher ERP on their repeater.
 

WQOC472

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That makes sence, Like i said in my previous post i am using this repeater for a few days until my VXR-7000 gets in. I was doing some calculations and my ERP on the this unit is around 58 ERP. But with my VXR-7000 i should be getting around 96 ERP.
 

SCPD

QRT
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Then again I could be wrong. Arkansas City PD is only licensed for 50 watts TX power. But they probably have less duplexer and feedline loss, and with a Stationmaster or DB408 or something more antenna gain.
 
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WQOC472

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Do you recommend I get a higher gain antenna when I start using the VXR-7000? I believe the PD uses a DB408 with LDF4-50A

Currently my antenna is up aprox. 40ft on a tower.
 

SCPD

QRT
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Virginia
I'm partial to DB408s mainly because you can put one up and forget about it for 20 years, handy when it's 200 feet up. And they seem to work better than the Stationmaster type in our mountainous terrain. But where you are something else may work better.
 
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LtDoc

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Oklahoma
I think I would check into how you have the mode, 'tones' and the frequencies set before jumping into new antennas etc. Your transmitting/receiving frequencies should be far enough apart that desensing shouldn't be that much of a problem.
If a signal isn't "keying" or "hitting" a repeater 'solidly' then it certainly can result in what you are experiencing. What would cause the repeater to not be hearing your signals 'solid' enough to turn on and work correctly? Signal strength is certainly one of the things affecting that, but probably not the most common 'mistake' or 'problem'. Check the things that are easy to check, then throw money at it.
Good luck.
- 'Doc
 

WQOC472

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Just FYI: The repeater is operating on RX:462.6000 (D025N) / TX: 467.6000 (D125N)



When my new VXR-7000 comes in i will be operating on 462.6000 (167.9) /467.6000 (167.9)
 

ramal121

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Back to the original question. You are definitely experiencing desense. That is when a strong off channel signal gets into your receiver and causes it to reduce its overall sensitivity thus making it harder to hear the intended on-channel signal.

You state that transmit from the portable to the mobile is clean. That means that there is no or little desense to cause a problem receiving the repeater. Now in reverse it sounds like the high power mobile transmit is causing enough desense to the portable that it is getting harder to hear the repeater.

The ability to overcome desense involves the selectivity (reject off channel signals) of the receiver, the amount of off channel signal getting to your receiver, and the signal strength of the intended on channel transmission (to overcome any desense present).

The difference between the GMRS repeater and the PD repeater is simply a better signal to your receiver to the point that desense is not a factor.
 

fineshot1

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NJ USA (Republic of NJ)
Just FYI: The repeater is operating on RX:462.6000 (D025N) / TX: 467.6000 (D125N)



When my new VXR-7000 comes in i will be operating on 462.6000 (167.9) /467.6000 (167.9)
If your repeater is rx'ing on 462 and tx'ing on 467 then you have it reverse of the norm
or did you make a mistake typing that out? That would be the norm for a portable or
mobile.
 

WQOC472

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My handheld's and Mobiles are RX on 462 and TX on 467. The repeater is opposite RX on 467 and TX on 462.
 

WQOC472

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ok - that's what i thought. just wanted you to realize your error in your post
cause if it was not an error that could cause problems for you and others
on that freq pair.
Thanks for seeing that, i did put it in wrong. My mistake...
 
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