Repeater Antenna - Poor Performance

[alcahuete]

I'm stumped on this one...

Just put up a local Mototrbo repeater for a neighborhood watch group. When I had the antenna propped up in the air temporarily for testing, the thing worked great. Was getting a 30 mile radius coverage without any issues at all. Was using a XPR5550e for the testing while mobile. Got 3-4 bars consistently.

I put the antenna up in its permanent mount (~10 ft. higher than the temporary) and now the range is severely limited. The 4 bars drop literally a block away from the repeater, and while it still goes out to around 15 miles, it now requires the full 40 watts to get in, when 20 used to suffice, and it sits at 0 bars on the meter, and consistently cuts out.

Nothing changed aside from putting the antenna up on the permanent mount. SWR is almost a flat 1.0:1, power output is fine. Duplexer seems fine, using 7/8" heliax aside from the pigtails.

I'm at a complete loss here, since absolutely nothing changed except raising the antenna higher. Have put up plenty of repeaters and radio systems in the past, and have never ran into this issue before.

Any ideas?

 

[riccom]

I'm stumped on this one...

Just put up a local Mototrbo repeater for a neighborhood watch group. When I had the antenna propped up in the air temporarily for testing, the thing worked great. Was getting a 30 mile radius coverage without any issues at all. Was using a XPR5550e for the testing while mobile. Got 3-4 bars consistently.

I put the antenna up in its permanent mount (~10 ft. higher than the temporary) and now the range is severely limited. The 4 bars drop literally a block away from the repeater, and while it still goes out to around 15 miles, it now requires the full 40 watts to get in, when 20 used to suffice, and it sits at 0 bars on the meter, and consistently cuts out.

Nothing changed aside from putting the antenna up on the permanent mount. SWR is almost a flat 1.0:1, power output is fine. Duplexer seems fine, using 7/8" heliax aside from the pigtails.

I'm at a complete loss here, since absolutely nothing changed except raising the antenna higher. Have put up plenty of repeaters and radio systems in the past, and have never ran into this issue before.

Any ideas?

what kind of coax are you using?

 

[alcahuete]

what kind of coax are you using?

7/8" heliax, aside from the pigtails.

What is really throwing me is that the damn thing worked great before I put it completely up in the air. ha ha! It's driving me nuts.

 

[riccom]

7/8" heliax, aside from the pigtails.

What is really throwing me is that the damn thing worked great before I put it completely up in the air. ha ha! It's driving me nuts.

ok and you said at 10 feet it was booming out 40 miles , when you put it up, it dropped amd cut out, is this a stand alone antenna, or is there another one or is this in a group of antennas?
is the cable tied off by wire or clamps?
second is what kind of antenna?
and have you checked to see if the coax was pinched, in the pigtails or pulled in any way?

 

[Thunderknight]

Was the same cable attached during testing? If not, the cable or connectors could be bad. Any chance the antenna got damaged during the install?
Is the antenna mounted in a way that might deform the pattern? (Eg side mounted). Can you bring the antenna back to the temporary setup (location and cable) and retest? Does it start working well again?

 

[alcahuete]

Thanks guys!

On the temp install, the base was right at about 15 feet. It was booming for sure out to around 30 miles, with a few dead spots here and there, but still working great. It is a standalone antenna on top of a residence. I checked all the coax including the pigtails, and it all looks fine. The cable is tied off with plastic zipties.

@Thunderknight, yes, the setup used in testing was completely identical. The only thing that is different is that the antenna is now mounted about 10 feet higher. It is mounted to a house, but it is above the house completely, so the pattern shouldn't be getting deformed.

If I can't get it figured out tomorrow, the plan is to put it back at the temp location and see what happens.

 

[riccom]

;power lines maybe, adjacent frequencies near by, and is this uhf or vhf?

 

[alcahuete]

;power lines maybe, adjacent frequencies near by, and is this uhf or vhf?

Closest power line is probably 10 miles away. UHF, no adjacent frequencies to my knowledge. Those variables should be eliminated anyway, as it worked fine before being permanently mounted.

 

[riccom]

Closest power line is probably 10 miles away. UHF, no adjacent frequencies to my knowledge. Those variables should be eliminated anyway, as it worked fine before being permanently mounted.

sounds like a bad coax or coax connector, i would test it with a nine volt battery and a small light, see if it shorts out

 

[alcahuete]

sounds like a bad coax or coax connector, i would test it with a nine volt battery and a small light, see if it shorts out

Will probably have to do that as part of the testing tommorrow.

 

[riccom]

Will probably have to do that as part of the testing tommorrow.

ok also check the connectors and give them a good cleaning, and seal up, the dust can do some damn crap to antenna connectors (living in phoenix i had the same issue)

 

[alcahuete]

ok also check the connectors and give them a good cleaning, and seal up, the dust can do some damn crap to antenna connectors (living in phoenix i had the same issue)

Yeah, I'm in the mojave desert, so definitely have dust issues. The coax and connectors are literally brand new....straight out of the box just for this project.

 

[riccom]

Yeah, I'm in the Mojave desert, so definitely have dust issues. The coax and connectors are literally brand new....straight out of the box just for this project.

with the santa ana winds and the fires and what nots, does not take much man, you are in a prime area due to it being so flat, so if it works better at 15 feet, roll with it!

 

[alcahuete]

with the santa ana winds and the fires and what nots, does not take much man, you are in a prime area due to it being so flat, so if it works better at 15 feet, roll with it!

Ha ha ha!! Yep! That's why the thing was working out to 30 miles. Actually would likely be considerably more, but the mountains get in the way at that point. Yeah...if I have to put it back in the original place, just going to do that.

 

[riccom]

Ha ha ha!! Yep! That's why the thing was working out to 30 miles. Actually would likely be considerably more, but the mountains get in the way at that point. Yeah...if I have to put it back in the original place, just going to do that.

well you have a few advantages, wind would not kill it, and more power to the antenna, less loss, and well its pretty damn cool looking!

 

[alcahuete]

well you have a few advantages, wind would not kill it, and more power to the antenna, less loss, and well its pretty damn cool looking!

Ha ha ha!! All good points.

Well I'll see what I can come up with tomorrow. If it wasn't so damn cold out (27 degrees....brrrrrrrr ha ha!) I'd be outside working on it now.

Thanks for the help!! I'll definitely keep the thread updated as to what I find out tomorrow.

 

[NC1]

The issue seems to defy logic, so the solution will in all probability also defy logic.

Where was the extra coax when it was in it's temporary position? Maybe the extra loop or two of spare cable was helping. Possibly it needs some ferrite clamps on the coax just below the antenna?

Double check the grounding as well just to cover the bases.

I have an antenna that works like a champ in only one spot on my 2nd floor deck, anywhere else and the performance drops off the cliff. I just left it where it works even if the mast is sometimes in my way.

 

[prcguy]

Stick a wattmeter at the antenna end and see if you have the expected power. If not move it down the line until you find the problem. You must have at least some basic test equipment if you own or operate a repeater.

 

[alcahuete]

Stick a wattmeter at the antenna end and see if you have the expected power. If not move it down the line until you find the problem. You must have at least some basic test equipment if you own or operate a repeater.

I thought I mentioned in the original post, but apparently not. Output power across the system was appropriate and SWR almost flat, hence my severe case of confusion as to why the hell this was happening.

Thanks guys for all the help!! I believe I found the issue. Still going to run some more extensive tests tomorrow with some long distance driving, but the tests tonight went amazingly well.

To add to the defiance of logic (@NC1 I know the feeling well, ha ha!), it appears as though the issue was a Male N Connector on one of the duplexer cables. I started at the repeater checking and replacing everything that could be replaced. I replaced the duplexer cables and took a drive. The cable on the transmit side appears to have had a bad connector.

To repeat, SWR was almost flat, output power was as expected throughout the system, and when things went bad, I also needed to double the output power of my radio just to get into the repeater. None of this makes sense to me with a bad connector on the output side. However, every time I put the old cable on, the problem occurred. Replacing the connector on the old cable also seems to have fixed the problem as well.

I'm not calling it a win yet, as it just doesn't add up for me, but so far so good.

 

[prcguy]

Does the bad cable have nickel plated connectors? These can create some low level IMD which will raise the noise floor in the receiver and limit range, but its usually not severe like you are describing. It would still be interesting to know if it has nickle plating and the replacement does not as in silver plated or something else.

I thought I mentioned in the original post, but apparently not. Output power across the system was appropriate and SWR almost flat, hence my severe case of confusion as to why the hell this was happening.

Thanks guys for all the help!! I believe I found the issue. Still going to run some more extensive tests tomorrow with some long distance driving, but the tests tonight went amazingly well.

To add to the defiance of logic (@NC1 I know the feeling well, ha ha!), it appears as though the issue was a Male N Connector on one of the duplexer cables. I started at the repeater checking and replacing everything that could be replaced. I replaced the duplexer cables and took a drive. The cable on the transmit side appears to have had a bad connector.

To repeat, SWR was almost flat, output power was as expected throughout the system, and when things went bad, I also needed to double the output power of my radio just to get into the repeater. None of this makes sense to me with a bad connector on the output side. However, every time I put the old cable on, the problem occurred. Replacing the connector on the old cable also seems to have fixed the problem as well.

I'm not calling it a win yet, as it just doesn't add up for me, but so far so good.