I operate a low power FM radio station. I have always had issues with high SWRs. Recently I have purchased a new transmitter, new antenna, and new 100 ft cable from the same company assuming they would work well together.

To test the system, I mounted the antenna as high as I could reach on my radio tower (about 5 feet). I had no trouble broadcasting at 100 watts at 5 feet.

I am in a very rural area, so it took some time but I found a tower climber to come out and mount my antenna on top of my tower. Now the antenna is at a height of 75 feet. Same antenna as at 5 feet, same cable, same transmitter. However, now that it is at 75 feet when I go above 30% power or 30 watts my SWRs become too high and the transmitter shuts off to avoid meltdown.

Any idea why it would work just fine at 100 watts at 5 feet, but won't operate above 30 watts at 70 feet? Could something be wrong with my tower?

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    $\begingroup$ hi there, Jim, welcome to the site! Can you add a little bit more detail to your question: what country/state are you in? what test equipment do you have available? what specific frequency are you set up for? what kind of feedline are you using, and what is its impedance? what is the nature of the grounding that you have set up for your tower & radio? what is the geometry of your antenna, including any radials\standoffs from the tower, where is it mounted (at the peak of the tower, off the side, etc.) adding this information to your question above, will help you get more specific answers! $\endgroup$
    – webmarc
    Commented Nov 19, 2023 at 1:51
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    $\begingroup$ and finally, how is the feedline connected to the antenna? $\endgroup$
    – webmarc
    Commented Nov 19, 2023 at 1:55
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    $\begingroup$ Did you inspect the connectors on the coax? Were they put on by the manufacturer? Did you test the cable for a bad/intermittent connection before using it? Is the cable strain-relieved on the tower? What brand antenna are you using and how does the manufacturer describe it? Was it manufactured/tuned for your particular frequency or not? It sounds like a bad connection to me; I think you should start there, but posting the details about the make and model of your antenna would help. $\endgroup$
    – Lou-in-USA
    Commented Nov 19, 2023 at 13:38
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    $\begingroup$ What kind of antenna is this? $\endgroup$ Commented Nov 19, 2023 at 15:06
  • $\begingroup$ Make friends with someone who owns an antenna analyzer. $\endgroup$ Commented Nov 21, 2023 at 3:28


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