Thursday, July 7, 2011

Attic antenna ghost's

Strange behavior.
Earlier this week I was getting the K3 and computer software ready for the IARU contest this weekend. The rig was on 20m (14.030) were I was able to get an SWR  around 1.4 and in that ball park from 14.000 to 14.060. This time when I did a software transmit check with N1MM contest software at 14.030 the SWR is now 2.18 Hmmmm. The other bands are up just a little bit but not as bad as 20m, we have had some very hot weather and I thought it was due to the hot weather maybe. I posted this question to Ham radio help at Yahoo groups. The consensus  seemed to be that with this type of antenna the heat should not affect it. In the past the other antennas were not affected by the heat. I did go up and have a peak at the Alpha Delta DX-EE to make sure nothing had happened to any supports or the antenna itself and all is well. The resonant frequency seems to be a lot higher than it was. For example 20m's was resonate at 14.200 and it is now 14.350 and it is similar on all other bands as well. Seems on Friday after work I may have to go up in the attic and play with the length as well as sweat and loose some weight in the attic.

5 comments:

  1. Strictly a shot in the dark! Do you have shingles on your roof? Do the shingles contain metal fragments in their construction? I wonder if the heat might have some affect on those shingles just above your wire. "Metal" shrinks in the cold and expands in the heat.

    Just a mad thought.

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  2. Hi Mike, that's a strange phenomena. Moist can make the SWR higher, but I think your attic is dry enough. Very strange... 73 Paul

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  3. Good morning Dick, that is a very interesting idea for sure and as I think about things I just may leave the antenna alone and see what happens when the cooler weather comes along. I have the tuner in the K3 that handles the mismatch no problem.

    Hi Paul, yes the attic is very dry other than the humidity that is in the air are muggy days. Other than that it is very dry up there

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  4. Hi Mike,

    I hope you find the cause of the higher SWR and post it. Strange! Does it drop at night when it's cooler? The ATU will tune it out at the rig, but of course you have some extra (minor) loss on the coax, which I take it is a very short run anyway. Good luck in the contest!

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  5. Hi Casey, I thought the other day I had it solved by changing out the coax to some spare LMR-400 I had in the attic. It seemed to be find then it was back up to the funny SWR. It really has not cooled down here at night to see if it is just from the heat.

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