Wednesday, March 9, 2011

Something went wrong.......but what

LP-100 displaying the bad news
On Sunday before I fired up the K3 on 30 meters to try the new attic dipole on the air with WSPR. I double checked the SWR with my MFJ analyzer and it was 1.4  . I was very surprised to see the SWR went from the 1.4 yesterday to 2.4 when I tried to transmit with my K3!!!! I went up to the attic (AGAIN) to have a look at the antenna just to make sure something did not happen  over night. It looked very good so I then I hooked up the antenna analyzer to the antenna and low and behold the SWR was now 2.4. I checked the coax with an ohm meter and all was good. I then removed the balun out of the picture and it was still 2.4 SWR. I then ran a short piece of
Murphy was discovered on the moon!!
coax from the antenna to my antenna analyzer and the SWR was still 2.4. I then checked the antenna connections at the mounting bracket and it was ok......the only thing I can try now it to adjust the height of the antenna in the attic maybe move it further away from some of the joist's. I was left scratching my head wondering why the SWR was good until I sent 3 watts into the antenna??? Then after that the SWR never again was 1.4 but 2.4, the 40 meter antenna was never affected by the attic joist's and the 20 meter dipole is about 4 inches away from the wooden roof in the attic. I guess if I was to look close there would be a post-it-note from Murphy's desk with a smiley face on it....I then made an adjustment to the antenna by lowering it's height just a little. On the MFJ analyzer that seem to do the trick again and the SWR was back down to around 1.4. Now it was time to put some power through the antenna and see if the SWR stayed the same or changed again. This time it did go up but only to 1.6 this is very odd as I have not had this happen before with any of my antennas.  Here is the next odd happening....I went on 30 meters WSPR and was not able to decode any signals and I was not being received by any other stations. My LP-100 did show I was putting out 1 watts to which I raised to as high as 5 and still nothing. I did switch over to 20 and 40 meter WSPR and all was ok seems I have to do more investigating with 30 meters.  Finally the other odd thing is the SWR will at times be  1.4 and will rise to 1.6 at times and stay there. Also as I adjust the sound card to the proper ALC reading I am not able to get the RF output to raise and lower when I adjust the RF on the K3. But on 20 and 40 meters all is ok. hmmmmm

11 comments:

  1. Hmm indeed. Although it is unlikely, one possible explanation of strange SWR readings and power output that doesn't follow the input is PA instability. A more likely explanation is a bad cable / connections, though that would affect all bands. But it is surprising how many problems of this sort have turned out to be the cable from the radio to the antenna.

    Having a dipole in the attic will affect it by lowering the frequency but after you trim bits off to get the best SWR in that position the SWR should not change.

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  2. Hi Mike, I am puzzled. I don't know what could be wrong. Very strange phenomena. I hope you, or someone else, knows what is wrong. 73 Paul

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  3. Good morning Julian, yes it is strange for sure....the odd part is the coax used for the new 30 meter dipole was from my 40 meter dipole. I ran new coax to the 40 meter dipole. So the coax when hooked up to the 40 meter dipole gave me no troubles...but that does not mean something went wrong when I moved it from the 40 meter dipole at one end of the attic to the 30 meter dipole at the other end of the attic. On the weekend I am going to do more investigating.

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  4. Good morning Paul, yes that it is strange for sure but ham radio is all about the challenge and solving stuff that just does not seem to be right at the time. So the weekend is fast approaching and I will see what I can do to solve the issue.

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  5. Have you checked your roof for heavy snow and ice? How about the roof itself. Any suspected damage? I found that when I had an attic dipole years ago, the swr changed with the amount of snow on the roof. 73 Dick N2UGB

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  6. Rain, snow, ice etc. will do this with an indoor antenna. Also check the braid ground on the pl259. If the analyzer is in the attic while checking - rf in the analyzer will cause strange readings. Look for any AC lines near antenna. Are yuu using an antenna tuner in the shack? If so, be sure the tuner in the rig is off - or they will fight each other and give that type of reading.

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  7. Your swr meter might need at least 2.5 watts to register properly.

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  8. Good morning Dick, as for the roof there was no snow up there and none now. But I would never had thought that snow on the roof would have any affect good to know.

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  9. Myles good morning and thanks for stopping by the blog. There are some AC lines that run along the attic in that area and I can look into that. There is no antenna turner being used at this time. I have the K3 and the tuner is in by-pass. Thanks for all the great info and it will keep me busy on the weekend.

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  10. If you have a dummy load, put it at the far end of your coax & then check the SWR at the rig. This will isolate the problem to either the coax or the antenna.

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  11. Good afternoon John....I had done that in the past and the SWR at both ends and all was ok....but I was thinking today and have a theory going to give it a go and see what happens.

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