Repeater setup issues

[sjmark24]

Hello all,

I'd like to just lay out my current repeater setup and would like some help with diagnosing a problem that I'm having with rx reception, for some reason there will be this intermittent problem of static and signal degradation to the point where the signal will drop for a second or two and then come back. Humidity does seem to play a part in this but here is the full setup and maybe someone can let me know what the issue is.


Repeater - Vxr-7000v

50' lmr 400 n type cable connected to lighting arrestor which is then grounded to a groundrod

rooftop mounted Commander technologies 220-3AN

TPL 250w amplifier

Duplexer from a local company (specs)
Frequency separation, MHz 0,6-15
Bandwidth, MHz 0,5-2,0
Max. input power (continuous-duty), Wt 250
Insertion loss RX-ANT, dB < 1,5
Insertion loss ANT-RX, dB < 1,5
RX isolation ANT-RX, dB > 90
TX noise suppression TX-ANT, dB > 90
Impedance, Ohms 50
VSWR < 1:1,2

 

[mmckenna]

50' lmr 400

This is the first thing that jumps out at me.

LMR-400 is good cable, but it's weakness is that the outer shield is made up of two different metals. When it gets damp, it creates a non-linear junction that will create all kinds of RF noise.
Take 250 watts, add a bit of moisture, and it'll cause issues like this.

All it takes is damage to the outer jacket, improper waterproofing of the connectors, or a leak at the antenna, and there ya go.

You might have more issues, but the first thing I'd do if it was mine would be to replace the LMR-400 with at least some 1/2 inch heliax cable. And make sure you waterproof all the outdoor connections.

After that, if it was still an issue, I'd start looking at your duplexer. "Duplexer from a local company" concerns me, as it's really easy for anyone to rebadge cheap Chinese stuff.

 

[sjmark24]

The thing is that it seems to be strictly an rx issue. When monitoring the repeater at the site i can hear the speaker playing the same static that is repeated. If I hit transmit with the base station mic theres no issues for anyone listening on the frequency, its just the rx side.

I'm thinking its an issue with the duplexer but I wont be certain until I replace the cable.

Thank you for your input

 

[prcguy]

I see a couple of problems right out of the gate. First off, loose the LMR400 and replace with Heliax cable immediately. Do not ever, under any circumstances use LMR cable on a full duplex system as its known to generate IMD which will show up as noise in your repeater receiver. Do that and you have fixed problem #1.

Second is you have a duplexer rated at 90dB isolation and that's assuming its properly tuned. You are running a 250W amplifier and I think you will need a 120dB rated duplexer or you will have to supplement your existing duplexer with several very narrow band pass or pass/reject cavities to get another 30 or 40dB isolation between your transmit and receive frequencies. Running a 250W amp on a repeater opens up all sorts of new problems. Maybe you should read this a couple of times and think about that 250W amp with 90dB duplexer: Duplexer Efficiency

Try running the repeater with no amplifier, just the stock repeater transmitter at maybe 25W and see how it works. That will lessen the duplexer isolation needs by 10dB and I'll bet its much better even with the LMR coax. There is really no reason to run 250W because most of the repeater users are probably using handhelds or modest power mobiles, why would you need to have a repeater transmitter that has 10X the power of the users talking to it? The only reason you might run 250W is when the users have pagers with little crappy internal antennas and you need to saturate a large area.

Hello all,

I'd like to just lay out my current repeater setup and would like some help with diagnosing a problem that I'm having with rx reception, for some reason there will be this intermittent problem of static and signal degradation to the point where the signal will drop for a second or two and then come back. Humidity does seem to play a part in this but here is the full setup and maybe someone can let me know what the issue is.


Repeater - Vxr-7000v

50' lmr 400 n type cable connected to lighting arrestor which is then grounded to a groundrod

rooftop mounted Commander technologies 220-3AN

TPL 250w amplifier

Duplexer from a local company (specs)
Frequency separation, MHz 0,6-15
Bandwidth, MHz 0,5-2,0
Max. input power (continuous-duty), Wt 250
Insertion loss RX-ANT, dB < 1,5
Insertion loss ANT-RX, dB < 1,5
RX isolation ANT-RX, dB > 90
TX noise suppression TX-ANT, dB > 90
Impedance, Ohms 50
VSWR < 1:1,2

 

[mmckenna]

The thing is that it seems to be strictly an rx issue. When monitoring the repeater at the site i can hear the speaker playing the same static that is repeated. If I hit transmit with the base station mic theres no issues for anyone listening on the frequency, its just the rx side.

Read what PRCGuy said so well.
It's not doing it when you are transmitting direct from the repeater because the repeater receiver is out of the equation. Even with the dissimilar metals in the cable, it'll transmit just fine because that's all it's doing, no RX.
When you transmit and receive at the same time, the receiver is picking up the noise generated by the transmitter and the cable issues.
So, that's sort of confirming that the coaxial cable is at least part of your issue.

I'm thinking its an issue with the duplexer but I wont be certain until I replace the cable.

I think the duplexer is the other part of your issue.

What's the reason behind running 250 watts on this repeater?

What brand/model duplexer is it?

 

[K5MPH]

I with pcrguy take the amp away and try it and replace coax,and why are you needing 250 watts any way.....

 

[prcguy]

After replacing the coax and dealing with the duplexer or additional cavity filters, I would also suggest adding an isolator right at the output of the amplifier if you keep it, or at the repeater transmitter output if you don't go with the amplifier. This will provide a constant 50 ohm match to the final amplifier and also to the input of the duplexer or additional filter that might be added.

The isolator will also protect your repeater transmitter and/or amplifier if the duplexer or antenna fails as the reflected power will be absorbed by the load on the isolator. The load is generally at least twice the power rating of the transmitter and if you keep the 250W amplifier a 150W load on the isolator would be appropriate.

 

[cmdrwill]

Repeater - Vxr-7000v
50' lmr 400 n type cable connected to lighting arrestor which is then grounded to a groundrod
rooftop mounted Commander technologies 220-3AN

TPL 250w amplifier

Duplexer from a local company (specs)

Alligator repeater. ALL mouth, no ears.

LMR400 cable at over 5 watts or so very BAD.

 

[zz0468]

I concur with the opinion that losing the LMR cable is the first thing you do.

Duplexer "from a local company"? I'm not sure what that means, but there are very few duplexers that I would trust at 250 watts, even if the "local company" specs it so. 90 db simply isn't enough isolation for that power level.

 

[kayn1n32008]

Alligator repeater. ALL mouth, no ears.



LMR400 cable at over 5 watts or so very BAD.

Bingo first thing after dumping the LMR409 would be to also dump that TPL amp.


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[sjmark24]

Read what PRCGuy said so well.
It's not doing it when you are transmitting direct from the repeater because the repeater receiver is out of the equation. Even with the dissimilar metals in the cable, it'll transmit just fine because that's all it's doing, no RX.
When you transmit and receive at the same time, the receiver is picking up the noise generated by the transmitter and the cable issues.
So, that's sort of confirming that the coaxial cable is at least part of your issue.



I think the duplexer is the other part of your issue.

What's the reason behind running 250 watts on this repeater?

What brand/model duplexer is it?

The need for 250 is the amount of coverage area needed for the repeater, this is covering 25-50 miles.

As for everyone elses questions, now thinking about it, the lmr 400 could be a huge culprit since I get the interference even if I run the cable straight into the repeater running in base station mode without any tx and just rx.

The duplexer could be the next problem but I think I will upgrade to the heliax first then move onto having the company that makes the duplexer to come to the site and take a look.

Its a 4 cavity duplexer if that helps anyone.

 

[kayn1n32008]

The need for 250 is the amount of coverage area needed for the repeater, this is covering 25-50 miles.



As for everyone elses questions, now thinking about it, the lmr 400 could be a huge culprit since I get the interference even if I run the cable straight into the repeater running in base station mode without any tx and just rx.



The duplexer could be the next problem but I think I will upgrade to the heliax first then move onto having the company that makes the duplexer to come to the site and take a look.



Its a 4 cavity duplexer if that helps anyone.

The club I belong to had a balanced repeater, 70+ mile RADIUS of mobile coverage, and the repeater only put 12.5w INTO the duplexer, then through 370’ or so of 7/8” hardline.

20-25 Miles does NOT need a 250w amplifier you will have an alligator, all talk not listen.

A 4 can duplexer will not cut it. 6 cavities of Band Pass/Band Reject, and as prcguy said, you will likely need additional band pass filtering on top of the 6 can duplexer.


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[zz0468]

The need for 250 is the amount of coverage area needed for the repeater, this is covering 25-50 miles.

Can we assume that the mobiles are all high power mobiles with gain antennas? It's usually desirable to match input and output coverage. If portables are used in the system as well, that 250 watts is not only grossly out-talking the portables, it's probably contributing to desense of the receiver so it hears the portables even more poorly.

There are sound technical reasons why people would question the 250 watt output. It takes very high quality equipment, from the transmitter and receiver, to the duplexer, feedline, and antenna itself, to get full duplex operation with that power level. And sometimes it's impossible to make it work perfectly.

The duplexer could be the next problem...

...Its a 4 cavity duplexer if that helps anyone.

A 4 cavity duplexer of any kind is probably not going to be adequate for the job of keeping a 250 watt transmitter out of is associated receiver. I've specified 8 cavity duplexers for that sort of service. They're huge, and hugely expensive. But that's what it takes to run a 250 watt transmitter in duplex service.

What is the make and model of the duplexer? Knowing that would help us help you.

 

[AK9R]

I'd like to just lay out my current repeater setup ...

What radio service is this repeater for?

 

[prcguy]

The OP is using commas to indicate fractions of an inch, usually meaning he is outside the US and his antenna model # indicates its in the 150MHz commercial range.

As mentioned in several different ways, assuming the repeater was working fine at 250W, users would be able to hear it at distances they would never be able to transmit through it. What good is a repeater that is full quieting at say 25mi but you can't key it up?

The OPs antenna model appears to be very good and it would be hard to improve on. Antenna height would be the next thing to consider in improving range once the transmitter power is dealt with and the duplexer and entire repeater system is performing the best it can be.

Edit: The OP might let us know what country he is in and some countries have ERP limits for human safety, which would affect the maximum power and antenna gain he could run.

What radio service is this repeater for?

 

[K5MPH]

How high is the antenna....