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Author Topic: swr question  (Read 522 times)
AE7GL
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Posts: 62




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« on: June 28, 2004, 02:25:55 PM »

I'm currently running a Diamond NR72BNMO (1/4 wave) antenna with an Icom V8000. Antenna is mounted in the center of the metal roof on a Ford Bronco. My current SWR's look like this...

near 144.000 swr is about 1.9
at 146.000 swr is about 1.1
near 148.000 swr is about 1.8

Is there a way to get the swr any lower at the top and bottom of the band? Or is this typical of a small antenna? I recall reading somewhere that the larger material (tubing) an antenna is made from the broader or flatter it swr would be. Is this right? Would this also apply to a longer antenna?

If so could I expect to get lower swr at the ends of the band by going to a longer (1/2 or 5/8 wave) antenna? I went with the shorter antenna to keep overall height down, but I still want to get the best performance possible too.

Any thoughts would be appreciated.
Thanks,
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N3ZKP
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Posts: 2008




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« Reply #1 on: June 28, 2004, 03:15:39 PM »

This is typical and is nothing to worry about. Anything under 2:1 on a 2m antenna is fine.

Lon
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AA4PB
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Posts: 12899




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« Reply #2 on: June 28, 2004, 07:09:41 PM »

The larger the tubing diameter, the broader the bandwidth. You cannot do the same thing by making the antenna longer - it needs to be thicker.
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AE7GL
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Posts: 62




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« Reply #3 on: June 28, 2004, 08:26:28 PM »

Thanks AA4PB. That's what I needed to know.
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W0IPL
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Posts: 410


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« Reply #4 on: July 04, 2004, 02:10:24 AM »

I think, were I you, I would look for something else being wrong.

When I read your results I thought that I remembered mine (quarter wave, NMO for 2M) being a lower SWR. So I went out and rechecked mine.  I show a 1.2:1 at both band edges and a 1:1 at 146 Mhz. As memory serves, it has been like this since I installed it in 1988 on my (then new) Pathfinder.

The first thing I would look at is the ground connection. If you did not scrape through the paint to bare metal or didn't use some type of anti oxidant to inhibit corosion, that may be your problem.

C Ya
 Pat
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AE7GL
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Posts: 62




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« Reply #5 on: July 11, 2004, 05:23:22 PM »

Just saw your post Pat. Thanks.

If grounding was a problem wouldn't the SWR's be higher all around? At 146mhz its fine.

I installed the antenna about 3 or 4 months ago and checked all the connections at that time with an ohm meter. Good continuity to ground. Nothing shorted. All looked fine then. Didn't get a chance to actually test it with an SWR meter until a couple weeks ago. That's when I posted the question.
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AA4PB
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Posts: 12899




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« Reply #6 on: July 11, 2004, 09:22:33 PM »

In my experience, it is not normal for a simple 1/4 wave whip to have an SWR under 1.2:1 across the whole 4Mhz of the 2M band. Now if you have a lot of feedline or other loss you might get that kind of reading at the transmitter end.
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