J-Pole Attic Antenna Install Troubleshooting Help

ccg_ga

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Nov 24, 2018
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Cumming, GA
I installed a J-Pole antenna from Snap-on Ferrite Beads in my attic recently and need some help to figure out why I am not able to get any signal out or hit local repeaters.

This is the setup:
  • Baofeng BF-F8HP handled w/ 8W
  • KB9VBR 2-MeterJ-Pole antenna w/ N connector
  • 3 Snap-on Ferrite Beads on the coax at the antenna (as recommended by KB9VBR)
  • The antenna is mounted to a length of schedule 40 pipe and attached to the plywood with a mounting plate
  • 3 hose clamps to secure the antenna to the pipe
  • All 3 hose clamps are under the "T" section of the antenna
  • Times Microwave LMR-400UF coax (40-45 feet run from the antenna to inside my shack)
  • RFN-1006-3I N Connector at antenna
  • RFI RFU-507-SI PL-259 at the end of the LMR-400UF cable
  • RFI RFU-536 Female-to-Female PL-259 barrel connector
  • LMR-400 jumper with PL-259 and SMA right angle connector to the Baofeng radio
  • I also made a jumper with RG-58 with a PL-259 and SMA right angle connector to test with also
When I key up to try and hit the closest local repeater I get nothing. Signal seems to not be making it to the repeater. I changed the antenna connection to a small mag-mount 2M antenna on my metal roof top and I can hit the repeater normally.

I hooked up my Surecom SWR meter to the J-Pole antenna and it doesn't read anything. No SWR reading, no power reading, just 0's.

I also checked both jumpers for continuity with a multi-meter and they read 0 on both coax connector center pins and also on the external housing of the connectors.

I'm stumped as to what to check next. Is the 8W the Baofeng possibly just not a strong enough signal by the time it makes it to the antenna?

The only other things 2 things I can think of are the metal film on insulation panels on the inside of the roof and that the AC/heat furnace units are about 6 feet away from the antenna.

I'll still pretty new to building my on antenna setups so the answer may be obvious and I just don't know what it is. Any help or suggestions are appreciated.

IMG_9886.jpg IMG_9887.jpg
 
Last edited:

nd5y

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Wichita Falls, TX
When I key up to try and hit the closest local repeater I get nothing. Signal seems to not be making it to the repeater. I changed the antenna connection to a small mag-mount 2M antenna on my metal roof top and I can hit the repeater normally.
It could be that the external antenna is wiping out the Baofeng's POS receiver but the repeater is hearing you fine.
Do you have or can you borrow a real radio to test on the antenna?
Can you arrange for somebody to listen to you both on the repeater and simplex?

I hooked up my Surecom SWR meter to the J-Pole antenna and it doesn't read anything. No SWR reading, no power reading, just 0's.
Probably another case of needing a second real radio to test with.
Is the meter known to be good?
Does the meter work when connected directly between the radio and a dummy load?

The metal inside the roof isn't good but may not be the main problem.
 

popnokick

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Several possibilities of things to check here. First is the fact you tested with a 2M mag mount antenna and hit the repeater normally. That means the Baofeng receiver is NOT being de-sensed or overloaded with signal from the repeater or nearby RF. To be certain, bring the 2M mag mount antenna into the attic and try it again there (rather than on the roof outside). That will help determine whether or not the metallic foil on your attic insulation is attenuating signals.... and by how much (if any). You don't need any other radio to do these tests. If the Baofeng and the mag mount antenna work with the repeater inside the attic then the problem is definitely with your J-pole installation and / or the coax and connectors.
Next, ditch the metal schedule 40 conduit. It's very likely the J-pole is coupling to it and detuning it to some degree. Replace the schedule 40 pipe with PVC... and consider replacing the metal hose clamps with wide zip ties or some other non-metallic attachment.
Finally - Your "0" readings on the Surecom are alarming. They suggest a short or open in your coax cabling / connectors. You wrote that you made up your own RG-58 jumper, so I'm assuming you also attached the other coaxial connectors yourself. That is a very easy thing to have go wrong, as it does very commonly when you attach your own connectors to coax cable. Very easy to make a mistake resulting in either a short or an open. When you test with a multimeter... and you must test EVERY cable and jumper.... ensure that the meter shows a SHORT (continuity) between the center pins on each end of the coax, then also test for a SHORT between the outer shell / shield of the connector at each end of the coax / jumper. If you don't get continuity then you'll need to redo the connector(s). Next, check each cable between the center pin and the shell / shield of the connectors for an OPEN (no connection). If you get a short / continuity between any center pin / shield, you will need to redo the connector(s). Good luck with your revised troubleshooting!
 

Ubbe

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I hooked up my Surecom SWR meter to the J-Pole antenna and it doesn't read anything. No SWR reading, no power reading, just 0's.
Then the connection between SWR meter and radio are faulty. Either short circuit or open. Use a standard volt/ampere/resistance meter and check the coax. First remove the coax from the radio and measure the coax end at the SWR that it is not short circuit. Then make a short at the coax at the radio side and measure at the SWR end that you see the short.

Don't bother checking j-pole or radio, they are fine. It is the coax or its connectors between SWR meter and radio that are the problem.

/Ubbe
 

ccg_ga

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Cumming, GA
@popnokick @nd5y @Ubbe Thanks to each of you for the reply and suggestions.

It could be that the external antenna is wiping out the Baofeng's POS receiver but the repeater is hearing you fine.
Do you have or can you borrow a real radio to test on the antenna?
Unfortunately not. I have an Icom IC-2730A in my Jeep but I don't have a power supply for it to run in the house. I wanted to test out this antenna setup first before I purchase another mobile radio/power supply for a base station.

Can you arrange for somebody to listen to you both on the repeater and simplex?
I do have another Baofeng UV-5R (I know, cheap radios) that I tuned to 146.000 simplex and my wife took it outside. She was able to hear me clear and vice-versa.

To be certain, bring the 2M mag mount antenna into the attic and try it again there (rather than on the roof outside). That will help determine whether or not the metallic foil on your attic insulation is attenuating signals.... and by how much (if any).
I did this and placed the mag mount antenna on top of some boxes in the attic. I was able to hit both repeaters I use normally with no issues.

Next, ditch the metal schedule 40 conduit. It's very likely the J-pole is coupling to it and detuning it to some degree. Replace the schedule 40 pipe with PVC... and consider replacing the metal hose clamps with wide zip ties or some other non-metallic attachment.
Thanks for this suggestion. I didn't think about that since the instructions on the KB9VBR site say it was fine to mount the antenna against another metal surface. I'll swap this out and see the performance differs.

I did some more testing with the multi-meter. Here are the results. The meter was set to Ohms with the continuity beep setting on.

radio-coax-tests.png

I did install all of the connectors except the N-Male connector on the LMR-400 that connects to the antenna (it was installed by the place I brought the cable from - Antenna Farm). Based on the replies I did determine that the RG-58 jumper was bad because of how I soldered the center pin connection on the SMA connector.

If I am interpreting these results correctly, I think the LMR-400 jumper is good since it has continuity between center pins and both outer connector shields and the OL reading on individual connectors.

The PL-259 connector that I installed on the LMR-400 is the problem since it reads 0.000 and not OL which indicates there is a short/continuity between the outer shield and center pin?

And here is where it gets interesting. On the Baofeng I have a SMA Female to Female adapter. I happened to bump the transmit button as I was loosening the coax and the radio hit the local repeater just fine. I think I may have had the adapter screwed too tightly, which was, in turn, causing the issue. I tried another repeater that is about 22 miles away and I was able to hit it fine as well.

IMG_9895.jpg

So, since that worked I hooked the SWR meter back up and here are the results from those tests:

radio-coax-tests.png

KB9VBR advertises a SWR of 1.2 or less at band center, and the reading on 146.000 is pretty much that so I guess the performance isn't that bad? 147.405 is the local repeater that is about 6 miles away.
 

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Ubbe

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KB9VBR advertises a SWR of 1.2 or less at band center, and the reading on 146.000 is pretty much that so I guess the performance isn't that bad?
The j-pole are a balanced antenna and the coax are unbalanced so you really need an adapter for that, a balun. Try and transmit while watching the SWR meter and touch the coax at different places. If the SWR changes you have a "hot" coax that radiate and are not decoupled from the antenna. Perhaps it is the coax that also works as an antenna now and makes the SWR readings worse.

/Ubbe
 

tweiss3

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How did you use a mag-mount on the roof? Do you have a metal roof? If so, you basically have a faraday cage over your attic and won't get RF out.
 

ccg_ga

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How did you use a mag-mount on the roof? Do you have a metal roof? If so, you basically have a faraday cage over your attic and won't get RF out.
Good point - I didn't make this distinction in the original post. The roof that I had the mag mount antenna on is metal, but it not the roof of the house. It's the roof over the front porch of my house. The roof of the house has typical shingles, but it is not metal. The metal roof over the front porch basically acts as a big ground plane for the mag mount antenna.
 

tweiss3

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Good point - I didn't make this distinction in the original post. The roof that I had the mag mount antenna on is metal, but it not the roof of the house. It's the roof over the front porch of my house. The roof of the house has typical shingles, but it is not metal. The metal roof over the front porch basically acts as a big ground plane for the mag mount antenna.
Fair enough. Know what I just noticed though, your roof sheeting is foil lined. I also see you have HVAC equipment and vents up there. All of that could be blocking your signal just like a metal roof. The quick check is to see if you can reach one of the repeaters from the attic with the HT in your hand with the stock antenna. My guess is you won't be able to.
 

enCrypt

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Was just going to say, first thing I noticed was the foil backed insulation boards! Your antenna is basically inside a Faraday Cage :oops:
 

popnokick

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READ the OP’s entire replies. He wrote -
I did this and placed the mag mount antenna on top of some boxes in the attic. I was able to hit both repeaters I use normally with no issues.
Therefore the foil-lined insulation is NOT the problem. It may be having some effect but is NOT preventing access to the repeaters he wants to use. The OP has ID’d the root cause as a bad coax/ connection. Again, read what was written and you will see this.
 

ccg_ga

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READ the OP’s entire replies. He wrote -

Therefore the foil-lined insulation is NOT the problem. It may be having some effect but is NOT preventing access to the repeaters he wants to use. The OP has ID’d the root cause as a bad coax/ connection. Again, read what was written and you will see this.
This is correct. I did some more research on the foil board on the inside of the roof. Adding this to the thread in case it is helpful to others in the future.

The inside of the roof is covered with a product called LP TechShield which is a radiant heat barrier (it deflects heat and keeps the attic cooler). It's constructed of a thin layer of aluminum which is laminated to an OSB (wood fiber) board. You can see the full details at the link below.

TECHSHIELD 7/16 in. x 48 in. x 8 ft. OSB Radiant Barrier-22493 - The Home Depot

I was able to hit both local repeaters (one is about six miles away and the other is 24 miles away) while in the attic with the mag mount antenna. I didn't have the mag mount antenna on a metal surface (ground plane), it was just sitting on top of some cardboard boxes.

When I was doing the SWR testing yesterday I was also able to hit those same repeaters with the J-Pole antenna.

Thankfully so far it seems that the heat barrier board is not totally killing my signal. I'm sure it is impacting it, but I am not sure to what extent.

I am going to make a couple of changes - change the J-Pole antenna mount to PVC pipe and re-do the PL-259 connector on the LMR-400 coax. Stay tuned for updates and new SWR measurements once those two items are complete.
 
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