Repeater troubleshooting

[wcpotter]

My guess is I am having a desense issue, but I'm not 100 percent sure.

 

The repeater works fine until I am about 1 mile away from the antenna site. Once outside of this area the audio from the mobile units stops getting through to the repeater. I know we are still reaching the repeater because we receive the squelch tail after attempting to transmit. The station ID from the controller can be heard loud and clear within a 3 town radius, so I know we are getting good coverage from the transmitter side of the repeater.

 

The duplexer has been tuned, we are using the proper jumpers for the duplexer, we are running 70 feet of 3/8" superflex andrew heliax. Brand new Comet antenna, etc. etc.

 

The only possibility I can seem to find through searching the internet is that there may be a bad jumper at the duplexer.

 

This setup was running at another site with no issues. The only thing that has changed is the feed line and the antenna.

 

 

 

 

[coryb27]

I would verify the repeater and radios did not somehow get programed to narrow band. Not a fan of comet antennas in full duplex operation, that's one place to look as well. Also did somebody swap the cables or tun the duplexer backwards? Let us know what you find.

[wcpotter]

I checked all the equipment last night to make sure it is all set for wideband operation.

 

When I was given the system the receive and transmit side of the duplexer needed to be re-connected, the rest were intact.

 

The duplexer is clearly labeled for receive and transmit. I can only assume it wasn't tuned backwards. Would you suggest swapping the two just in case or would that cause damage?

 

The antenna we have is a Comet CA-712EFC, the same antenna the prior operator used.

[n4gix]

That is the same antenna that I'm running, although mine is fed with 60' of Comspec 1/2" heliax. Have you access to an antenna analyzer? If so, sweep the system at both your transmit and receive frequencies to see what the precise VSWR and impedance are.

[coryb27]

 I would check the SWR between the transmitter and the duplexer and see what you get. I am leaning toward duplexer due to the vanishing audio. When is the last time it was tuned? Also, you did not mention the the type of repeater.

[wcpotter]

The system is made up from the following components:

 

TYT TH-9000D for the receiver & transmitter. Transmitter hits the amp with 10 watts drive.

Telewave duplexer

ID-Omatic 4 controller

Henry amplifier

[wcpotter]

I tuned the receiver to a frequency that transmits from about 3 towns away and my system received it loud and clear and passed it through to the transmitter with no issues.

 

I'm beginning to think that the terrain, current antenna height are working against me on the receive side. Wondering if its worth getting a receive preamp.

[coryb27]

So this was tested without a duplexer? If so it sounds like you are hearing ok. What kind of duplexer are you using?

[wcpotter]

It is a telewave duplexer.

 

I tested the receive using non-gmrs uhf frequencies with the duplexer inline & everything worked fine.

[zap]

Duplexer sounds out of tune. Is it a cavity style or mobile style?

 

Sent from my SM-T350 using Tapatalk

[wcpotter]

Cavity style

[wcpotter]

I did a bit more troubleshooting yesterday as I heard someone trying to use the repeater. Same thing, no audio.

 

When I shut the transmit radio off I could hear the user crystal clear, turned the transmitter on & no audio on receive.

[coryb27]

yea that's a bad duplexer, did you try reversing the tx and rx leads into the duplexer? I have seen people tun them backwards before.....

[wcpotter]

I tried reversing the tx & rx and it got worse, so I have ruled that out.

 

Do duplexers ever "go bad" or is it just out of tune perhaps?

[coryb27]

It is out of tune unless filled with water or hit by lightning

[rfmedic]

Ok the issue you're having could be one of several things so I'll break it down.

 

1: The radios you are using are not very well filtered and were never intended for duplex operation. The receiver may still be seeing the transmitter locally. Try bypassing the Henry amplifier and see how the performance of the system is.

 

2: Henry amplifiers suck and can be spurious. I have had dozens of them crap out over the years. Bypass the amplifier for now.

 

3. Have you performed a defense test? Have someone go out to a drop out location while you are in front of the repeater. Have them transmit and while they are talking. Shut off your repeater transmitter and see if the signal improves on the receiver.

 

4: What else is at your site? You may be fine internally to your repeater, however it does not sound as if you are utilizing any form of intermod protection (I.E. Isolator, circulator panel etc...) There may be some other repeater or transmitter that mixes with your transmitter and is causing inter-modulation which in turn would dramatically kill off your receive radio's sensitivity in full duplex mode.

 

RfMedic

[wcpotter]

I bypassed the Henry amp, set the transmit radio to high power & noticed no difference in regards to the issue I am having.

 

I have had people out in the field and I am able to receive them loud & clear with the transmitter off, turn the transmitter on & I lose their audio, but still receive the signal.

 

Nothing else is at my location that would cause any interference.

 

All the cabling for the duplexer is rg-214/u except for the output to the receiver & input from the amplifer.......those are lmr-400.

 

I know the rg-214/u is the proper cable to use between the duplexer cavities, antenna input, etc., but Is the LMR-400 ok to use for the receive & transmit sides of the duplexer? If not I'm guessing that could be the problem perhaps?

 

This system was given to me setup this way, so I am working through all the bugs myself.

 

Keep the feedback/tips coming!

 

Thanks

[n4gix]

Honestly I suspect duplexer issues. Possibly in moving to a new location it was knocked out of tune. I bought a spectrum analyzer so I can tune duplexers, circulators, etc., but if you don't have one or access to one you'll need to carry it to a shop that can check the tuning.

[coryb27]

when is the last time that duplexer was put on a spectrum analyzer? It is way off freq.

[wcpotter]

I have a local radio shop that will put it on the bench and tune it if need be.

 

Can someone confirm that the LMR-400 cables that are being used to connect to the receive & transmit sides of the duplexer are correct?

 

Thanks

Chris

[coryb27]

The LMR 400 is fine for that, just stay away from it as a feed line as it preforms poorly in full duplex operation.

[Logan5]

My duplexor came with LMR400 jumpers. I see no issue other than lack of flexibility during install and maintenance.

[linboogy]

Not sure but I have read a few comments about modern LMR has a coating on the shield foil making it non conductive to the braid to prevent the duplex problems now. Anyone have conformation of this?

[JohnE]

Not sure but I have read a few comments about modern LMR has a coating on the shield foil making it non conductive to the braid to prevent the duplex problems now. Anyone have conformation of this?

also known as LMR 400 flooded

https://www.tessco.com/products/displayProductInfo.do?sku=44370&eventPage=1