Laird FG4607 UHF GMRS Repeater Antenna

[SpugEddy]

Following this thread. Very interested to see the
outcome.
Only thing I would try next is to use PVC on the bracket.
Use a long enough piece to get the antenna above the
sheet metal. Total isolation between antenna and sheet
metal

 

[AA4TX]

My thoughts are along the lines of RFI-EMI-GUY. You could be getting RF into the SWR meter due to the close proximity of the meter to the antenna. It would be worth recording what you get with the meter placed at the transmitter. And as already mentioned, make sure your short service cable is intact.
Have you tried a dummy load in place of the antenna?

AA4TX

 

[BlueDevil]

UPDATE: I brought the antenna down off the mountain (again) to test its performance. Everything continued to check out fine. The RG-214 tested fine both with a SWR meter and continuity test.

I was able to install the antenna on a different roof top mountain base. The new one is all galvanized metal with support brackets and nuts and bolts holding everything together. The previous base was a painted style pole that is commonly seen with satellite TV dishes. I never could get it so tighten up like I wanted. The new base seems to have solved the problem. I am now getting an SWR reading of 1.24 both at the antenna and at the beginning of the feedline going to the antenna.

I am now dealing with issues related to my Icom FR4000.

Thanks for everyones help!

 

[SpugEddy]

Amazing how something so simple and trivial can cause
such havoc. Glad you're straightened out

 

[mmckenna]

Amazing how something so simple and trivial can cause
such havoc. Glad you're straightened out

Exactly why many radio techs are going partially bald and/or are experts at day drinking.

 

[RFI-EMI-GUY]

UPDATE: I brought the antenna down off the mountain (again) to test its performance. Everything continued to check out fine. The RG-214 tested fine both with a SWR meter and continuity test.

I was able to install the antenna on a different roof top mountain base. The new one is all galvanized metal with support brackets and nuts and bolts holding everything together. The previous base was a painted style pole that is commonly seen with satellite TV dishes. I never could get it so tighten up like I wanted. The new base seems to have solved the problem. I am now getting an SWR reading of 1.24 both at the antenna and at the beginning of the feedline going to the antenna.

I am now dealing with issues related to my Icom FR4000.

Thanks for everyones help!

Curious what issue you are having with the repeater, because, if the power amplifier is oscillating or otherwise creating out of band signals, your VSWR may reflect (pun intended), that. Of course very bad VSWR can cause transmitter spurious signals as well, so you can end up chasing your self.

If you have a circulator/ isolator, you can improve things.

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[BlueDevil]

Apparently the FR3000/4000 series repeaters have a known issue where the Repeater continuously transmits very low signal on the TX frequency. It is noticeable with a handheld radio. Holding the radio within a 1ft or so will detect a carrier and the signal strengthens as you hold the radio closer to the frame.


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[BlueDevil]

Here is a link to the thread: https://r.tapatalk.com/shareLink?sh...ence.com/showthread.php?t=331546&share_type=t


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[RFI-EMI-GUY]

Apparently the FR3000/4000 series repeaters have a known issue where the Repeater continuously transmits very low signal on the TX frequency. It is noticeable with a handheld radio. Holding the radio within a 1ft or so will detect a carrier and the signal strengthens as you hold the radio closer to the frame.


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I think the Motorola MSF5000 did the same.

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[jeepsandradios]

All of my FR3000/4000 repeaters do that. As others have said the MSF also did that. I have never seen an issue on my FR4000 due to this, other than my carrier light going on when i am in the shelter with the repeater. As soon as i walk outside it clears. Make sure your chassis is grounded along with your other equipment and you should be good.

 

[mmckenna]

Apparently the FR3000/4000 series repeaters have a known issue where the Repeater continuously transmits very low signal on the TX frequency. It is noticeable with a handheld radio. Holding the radio within a 1ft or so will detect a carrier and the signal strengthens as you hold the radio closer to the frame.


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Probably noise from the local oscillator. I've got some Motorola XTL consolettes that will do this.

 

[BlueDevil]

So the issue with very high SWR readings at the antenna has come back up. Today when visiting the site I noticed that the SWR readings on the feed line and at the antenna were consistently around 6.0. However when I hooked up my Bird Watt Meter to the TX port of the repeater with a dummy load I also noticed that my repeater had not been putting out any power.

I ended up swapping repeaters. Now my repeater is putting out 40watts right out of the back and about 20-22watts after the Duplexer (seems like a fair amount of loss?). While testing the repeater output I also checked the reflected power and to my amazement I found very little, just enough to make the needle budge on the meter. This seems like an odd finding to me. If my SWR Readings are back up around 6 shouldn't my reflected energy be much higher? Could I be getting false SWR readings from RFI/EMI being picked up by the antenna?

I left the repeater on and operational to test it as I came down the mountain and back into town. The receiver seems to be almost completely deaf. A strong mobile station can sometimes get into the repeater however a handheld has no chance. This repeater is positioned about 2500ft above the valley that I live in with a direct line of sight. In fact I can talk simplex on a handheld back to town without issue. Although the transmitter sounds great! The carrier on the hang timer and the occasional CW ID transmission are at full quieting.

The location that this repeater is installed at has a fair amount of Point to Point Internet Networking Equipment with associated network switches and other networking equipment. The building and equipment doesn't seem to be particularly noisy with RFI/EMI. But there is clearly something desensitizing the receiver.

 

[mmckenna]

Is it possible you duplexer is out of tune?
I'm trying to read back through your posts to see where you made the SWR measurements. I'm not entirely clear on how/when/where you did this.

Testing SWR -at- the antenna can be problematic.

All your testing on the individual components seem OK, or that's what you've said.

I don't see any mention of testing the duplexers. If your duplexer is out of tune, that would/might explain a lot of the other issues, like receiver desense, weird SWR at the repeater, etc.

For the repeater that is now showing zero RF output, if the SWR is high, it will throttle back, or could be damaged by high SWR. Many years ago we found our MSF5000 VHF was putting out very low power. Turned out to be a heliax connector messed up by other work on the tower. Had to have the amplifier repaired. Not sure I would have put the other repeater in there until I solved this.

 

[RFI-EMI-GUY]

So the issue with very high SWR readings at the antenna has come back up. Today when visiting the site I noticed that the SWR readings on the feed line and at the antenna were consistently around 6.0. However when I hooked up my Bird Watt Meter to the TX port of the repeater with a dummy load I also noticed that my repeater had not been putting out any power.

I ended up swapping repeaters. Now my repeater is putting out 40watts right out of the back and about 20-22watts after the Duplexer (seems like a fair amount of loss?). While testing the repeater output I also checked the reflected power and to my amazement I found very little, just enough to make the needle budge on the meter. This seems like an odd finding to me. If my SWR Readings are back up around 6 shouldn't my reflected energy be much higher? Could I be getting false SWR readings from RFI/EMI being picked up by the antenna?

I left the repeater on and operational to test it as I came down the mountain and back into town. The receiver seems to be almost completely deaf. A strong mobile station can sometimes get into the repeater however a handheld has no chance. This repeater is positioned about 2500ft above the valley that I live in with a direct line of sight. In fact I can talk simplex on a handheld back to town without issue. Although the transmitter sounds great! The carrier on the hang timer and the occasional CW ID transmission are at full quieting.

The location that this repeater is installed at has a fair amount of Point to Point Internet Networking Equipment with associated network switches and other networking equipment. The building and equipment doesn't seem to be particularly noisy with RFI/EMI. But there is clearly something desensitizing the receiver.

You haven't said much about what's on the mountain. And it could be trouble.

I will tell you a story. About 30 years ago I was responsible for UHF repeaters in Chicago. This included the Sears Tower and the John Hancock building. The John Hancock building was a bit of a sketchy site with a lot of old stuff, FM broadcasters and no vertical separation between the LMR and Broadcast antennas. In fact, inside the Radio room, there were FM broadcast rigid lines, 90 degree elbows, very messy. In that corner, I actually felt I was having short term memory problems. A lot of power.

Anyway, before I went out there the first time, a co worker told me to be prepared to see 8 to 10 watts coming back on any antenna line constantly from those broadcasters. He was right, there was that much power on the Bird wattmeter. The repeaters had T1504 cavities and MA COM triple circulator, so there was protection from that out of band energy.

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[jeepsandradios]

I ended up swapping repeaters. Now my repeater is putting out 40watts right out of the back and about 20-22watts after the Duplexer (seems like a fair amount of loss?). While testing the repeater output I also checked the reflected power and to my amazement I found very little, just enough to make the needle budge on the meter. This seems like an odd finding to me. If my SWR Readings are back up around 6 shouldn't my reflected energy be much higher? Could I be getting false SWR readings from RFI/EMI being picked up by the antenna?

What are you using to test SWR ? You mentioned a Bird Watt Meter. If you showing 22F/0R then your SWR is fine. Where do you get 6 from ?

 

[BlueDevil]

The Mountain Top Site that I am using is used primarily by an Internet Service Provider providing wireless internet. It has networking equipment and Point to Point Microwave connections. None of it seems particularly noisy.

I had a really odd experience today. Suddenly without explanation the Repeater started working beautiful in the middle of the day for a few hours and then suddenly it stopped receiving again. The Repeater was providing very strong coverage area of at least 40+ miles. It had full quieting and was performing exactly like I have been anticipating.

We haven’t had any significant weather chances. Cold, Fog, Freezing Fog... The Repeater is still transmitting a very strong signal with the CWID transmissions.

This is starting to make me believe that I could have an issue with the receive side of the duplexer. Something is lose and may have some how vibrated back into position. Maybe there was a temperature change inside where the duplexer is stored that caused it to operate a little differently. This seems like the only thing that would allow the Repeater to suddenly go from being “deaf” to fully operational and back again within a few hours during the middle of the day.


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[RFI-EMI-GUY]

The Mountain Top Site that I am using is used primarily by an Internet Service Provider providing wireless internet. It has networking equipment and Point to Point Microwave connections. None of it seems particularly noisy.

I had a really odd experience today. Suddenly without explanation the Repeater started working beautiful in the middle of the day for a few hours and then suddenly it stopped receiving again. The Repeater was providing very strong coverage area of at least 40+ miles. It had full quieting and was performing exactly like I have been anticipating.

We haven’t had any significant weather chances. Cold, Fog, Freezing Fog... The Repeater is still transmitting a very strong signal with the CWID transmissions.

This is starting to make me believe that I could have an issue with the receive side of the duplexer. Something is lose and may have some how vibrated back into position. Maybe there was a temperature change inside where the duplexer is stored that caused it to operate a little differently. This seems like the only thing that would allow the Repeater to suddenly go from being “deaf” to fully operational and back again within a few hours during the middle of the day.


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Have you performed a effective sensitivity and desense tests on the repeater?

Circling back to your high VSWR. Could the antenna have a loose part inside?

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[BlueDevil]

Have you performed a effective sensitivity and desense tests on the repeater?

Circling back to your high VSWR. Could the antenna have a loose part inside?

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I don't have the equipment to perform an "effective" sensitivity and/or defense test on this repeater. I could do some basic field testing...

When the repeater had that brief period where it was fully operational I didn't notice any signs suggesting that the transmitter was deceasing the receiver. However the receiver side of things has been very intermittent. This is causing me to lean towards a possible duplexer problem. When connecting the antenna straight into the receiver and operating the repeater as a base station I am able to receive signals very well without any noise or signs of interference.

 

[BlueDevil]

Here are some pictures of the duplexer I am using...

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[RFI-EMI-GUY]

Here are some pictures of the duplexer I am using...

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Ok, that is a notch type duplexer. It has reject tuning only. It is a common duplexer, but not as ideal as a band pass/reject type filter duplexer.

Tuning is critical to get the notch depth as good as possible on each section and leg. The jumpers are critical length. Make sure they are the ones for that duplexer. and are for or near the frequency of operation. Make sure they are not damaged.

The BNC connectors are problematic, if silver, they may be tarnished needing clean up. If nickel plated watch out for green corrosion. The connectors may need to be tightened up so that the shield and center conductors mate tightly.

Who tuned the duplexer? Is it tuned properly?

But before that, let's go back to the high VSWR which was the original complaint. And try these things.

Connect the wattmeter directly to the transmitter and feedline. Send an assistant to the roof with a 10 foot section of PVC pipe. From that distance have the assistant lightly thump and push the antenna radome as well as the feedline connection and watch for any abrupt VSWR changes.

If the antenna checks out, reinstall the duplexer, send the assistant out to town to transmit while you enable and disable the transmitter in a crude desense test. While doing this, manipulate the duplexer cabling and note any changes.

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