[TowerTalk] Maddening Problem Revealed

Kim Elmore cw_de_n5op at sbcglobal.net
Tue Dec 30 10:51:37 EST 2008


Last night, when there were signals to be heard on 160 m, I began 
some listening tests. I have a set of K9Ay loops for low band rx. 
Even with a mismatch, the shunt fed vertical should hear well, but I 
found that it was at least 10 dB down (by ear) from the loops, 
*without* the loop's preamp.

This morning, I've substituted a known good transmission line for the 
one in use but that changed nothing. So, I looked carefully at the 
the connector I used for feeding the shunt:  a PL-259, the center 
feeding the shunt and the shell grounded. The part I could see looked 
fine, but when I fed about 20 w to it, it got warm.  Not right.

So, I removed it and looked in the other end. It's filled with 
carbon. That is the problem. I'll replace it with a real feedthrough 
and use a separate ground lug.  Someone asked if I were using 
feedthroughs and I said no, But, I should have been! I had forgotten 
that I had a couple of old ones and, instead of using the proper 
components, I used what I had on hand. I should know better.

Now, If I can just figure out how moisture is getting into that box, 
I'll be set. Actually, I think what I'll do is drill some 1/4" to 
1/2" screened holes in the bottom, so any moisture that gets in has a 
way out, but with screen small enough to keep insects out.

My thanks to all who responded.

Happy New Year,

Kim Elmore, N5OP 



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