Project pays off

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Posted by w0ep on July 12, 2018 at 8:47 pm

[Yesterday: 3 miles of hill workout in Columbus]

I feel like I was just in time on the monitoring box because my transmitter has been heating up due to antenna feedline mismatch.

Radios, particularly transmitters, want to see a certain electrical quality in the antenna in order to transfer the maximum power to the “air”.  If things are mismatched, some of the power is reflected back to the transmitter which then causes the transmitter parts to heat up.  The mismatch is measurable and  frequently described in turns of standing wave ratio – SWR.  An SWR of 1:1 is a perfect match.  The SWR is determined by the impedance of the feedline and antenna taken as a complete system. Impedance is a technical term, it depends on the physical properties and the frequency of the radio energy being transmitted.

I think maybe I’m getting some moisture into my feedline somewhere. That messes up the impedance. My SWR is not so good and the transmitter is heating up and the air conditioner isn’t able to keep up with the whole thing on 90+ degree days.  So I have cut the total output back to about 50% of normal and I fooled around with a lightning arrester that I had in the line.  Between those two things I have the transmitter working in a sustainable way.

Yesterday I ordered some new feedline, new lightning arrester, and connectors from MFJ over in Starkville.  I have all of that in my hands now.  I need to do some work on end connectors for the new cable, then find a day that I can get up the tower and swap out the new for the old.  Maybe Sunday?

Until I get that done I’ll be running less output and keeping an eye on the temperature… which is exactly what my new monitoring box allows me to do from my desk yahoo!

 

Filed under classic book radio
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3 Comments

  • On July 13, 2018 at 10:33 am Jonathan Howard said

    Just curious, did you paint roof silver or otherwise light or reflective color? Also insulate the roof and walls?

    • On July 13, 2018 at 11:56 am w0ep said

      I did insulate the roof and walls, but the roof covering is just regular asphalt shingles, mostly grey.

  • On July 14, 2018 at 10:06 am jonathan howard said

    You did all you could w/in constraints of residential aesthetics.

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