Laurence, KL7L / WE2XPQ, sent this picture of his 2200-meter loop coupler after his WSPR-15 session last night:
what do you get when you put 55 amps of 137 kHz RF though a stainless steel bolt?
Laurence indicates the following in a post of the European LF reflector:
“The Stainless 5/16th bolt in the feedthru must have had some imperfections in manufacture and got extremely hot at circa 50-60A 🙂 it didnt happen to the other bolt and wasnt at the wire connection points each side.
I think Ive had it with feed thrus’ at this current and are going to come straight in thru a hole drilled in a hi density cutting board.
I recall the original brass feed thrus getting a little warm but this must have got real warm – sufficient to say the Decca kept on transmitting and didnt see a high SWR at all over the past week…
The Walmart Rubbermaid box was (is) in its 12th year and Im just going to plate over it… “
I’ve seen heating on brass and bronze as well and his plan to go straight through the plastic is probably sound. I have nightmares about this kind of stuff. Its also curious that the other insulator was fine since the current through each conductor should be the same. There had to have been some current path along the plastic box, in my opinion.
Be careful out there!