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Author Topic: High SWR on 2M  (Read 1034 times)
KD8TZC
Member

Posts: 67




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« on: April 23, 2013, 04:46:41 PM »

So this weekend I installed a new Slim Jim 2M antenna.  I tested the antenna out and it has a nice SWR under 1.4 across the entire 2M spectrum.  Only problem is when I installed in, ran the RG8/U from the attic to the basement, hooked it up to the SWR meter and the radio, I get an SWR > 5:1.  I decided to hook a dummy load up at the end of the coax line and test the line, and the cable int the dummy load is generating > 5:1 SWR.  So, I don't think it is the antenna, but what could it be?

I ran 100' of RG8/U from the basement to the attic.  I do have excess cable in the attic in case I want to move the antenna to another portion of the attic.  Would excess cable cause this though?  Should I wrap up the excess cable neatly (right now it is just strewn on the attic floor)?  Is the cable bad or could it be something else?

I was all set to assume the cable was fine and just the location of the antenna was the issue... I have no issue how to deal with a high SWR on an antenna.

Thanks,

John
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John - KD8TZC
K2OWK
Member

Posts: 1077




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« Reply #1 on: April 23, 2013, 04:51:30 PM »

If the end of the antenna cable into a dummy load is giving you a >5 to 1 VSWR. It is in the cable. Most likely one or both connectors.

73s

K2OWK
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KD8TZC
Member

Posts: 67




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« Reply #2 on: April 23, 2013, 04:53:49 PM »

I soldered the connectors on, so I guess that could be a possibility.  Is there something I should look for or a way to tell if the connector is the cause?
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John - KD8TZC
WB6BYU
Member

Posts: 13567




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« Reply #3 on: April 23, 2013, 04:55:41 PM »

Actually a long cable will tend to give you a LOWER SWR at the rig than at the antenna
due to losses in the cable.

Look carefully at the two connectors on the cable:  likely failure points are the braid
(spin back the outer shell to confirm that the braid is properly soldered to the connector)
and the center pin (not soldered, or has come loose).  I often find connectors where the
shield is not properly terminated.

Or you may have shorted a connector when you soldered it.  A quick test is with an ohmeter
or other continuity tester:  you should measure a short circuit from one connector shell to
the other, and from one center pin to the other, but it should show open if you test either
pin to the shell of the connector.
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KD8TZC
Member

Posts: 67




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« Reply #4 on: April 23, 2013, 05:27:46 PM »

Well, I figured it out... nice and easy.  I cut off the connector near the radio as it is the easiest to access, and soldered a new connector on it.  Hooked it back up to the dummy load, and had almost a 1:1 match. 

Only problem I have now is many of the channels that I tune to (not all) have high levels of hash. I turn the sql all the way up and still all hash.  If I sent (to a repeater) and then listen, I can hear the silence at the tail of my transmission from the repeater for a second or two, and then back to hash.  I have a feeling this will be a tougher thing to diagnose.  I thought maybe it was the CFL's or LED lights in the house, but I turned most of the lights off and still that way.  Hmmmm.... dumb question, but do they sell a filter to reduce the interference?

Thanks all for your help,

John
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John - KD8TZC
K7KBN
Member

Posts: 2835




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« Reply #5 on: April 23, 2013, 09:32:11 PM »

Did you have the noise problem before?  Do you have/can you borrow another radio (maybe an HT) just to see if it, too, has noise?

If both radios have the same noise, you're going to have to look around your house to find the source.  There are a lot of things these days that produce some pretty severe noise.

And by the way, to answer your question about testing coax and connectors, use a multimeter to check for continuity between center and shield with both ends of the coax disconnected.  (There should be an open circuit.)  Wiggle the connectors around while watching the meter and see if there's intermittent continuity.  Apparently, you found the faulty one by ... ESP?!  Grin
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73
Pat K7KBN
CWO4 USNR Ret.
KD8TZC
Member

Posts: 67




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« Reply #6 on: April 24, 2013, 04:43:30 AM »

Yes, I have a mobile unit in my car and an HT that both get the noise.  At night it is worse that daytime.  I'm thinking it could be the street lights.  We have one (across from my house) that constantly cycles on and off.  I have let the utilities company know about this multiple times, but they have yet to come out and fix it.  Maybe I should throw rocks at it to bust it out.  lol...

Even in the daytime though there is still some noise on some channels.  127.210 seems to get it bad at all times of the day and when I drive through the neighborhood, it will come and go, but normally I can squelch out the static in he car if I turn the sql up high enough.  What I might do is kill all the fuses' in the house except the one that feeds my ham shack, and see what happens.  If that quiets the noise, then I know it is in my house.  I can then turn each one on one at a time and see which ones bring the noise back.  I do have a number of WiFi Access points in the house, but I don't know what frequency those broadcast on (I would presume they are not in the HAM bands, but you never know).

The HT doesn't pick up the noise as bad as the other units, and I'm going to presume that is because the antenna has less gain than the others.  I wonder if there is a device that would allow me to introduce attenuation on the antenna line to see if that would kill the noise if I can't isolate it somehow?

The continuity tester thing wouldn't have worked as I would have had to uninstall all the cable to do the test (or have a multitester with a lead that could go from my basement all the way to the attic access on the second floor.  I just got lucky with the one end I picked.
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John - KD8TZC
K2OWK
Member

Posts: 1077




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« Reply #7 on: April 24, 2013, 01:04:42 PM »

The cable can be tested from one end if necessary. Test from the center pin to the outside, it should read open. Then go to the other end and short the center pin of the connector to the outside. It should read a short from the center pin to the outside of the connector. This will tell you if the connector is shorted to the shield (first test), and that the center is connected to the center of the coax. While it is not the best way to test it. It will work in a pinch.

73s

K2OWK
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KD8TZC
Member

Posts: 67




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« Reply #8 on: April 25, 2013, 10:21:37 AM »

Just an update on my noise issues that I continue to see.  Only happens at night, so I happen to believe that this is related to lighting.  I have contacted the power company that maintains the light poles in our neighborhood to see if they will fix the one that constantly turns on and off all night.  I'm not sure if that is the culprit for this, but I'm sure it is causing some noise.

What I did though for the noisy channels on 2M was to enable Tone Squelch on the frequencies that are on a repeater and that has a PL tone that is required.  Worked like a charm!  I know this won't work always as some repeaters don't always use a PL tone.

John
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John - KD8TZC
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