Topband: Verifying integrity of 75 ohm coax.

[Jim GM]

What is making you believe you have a faulty 75 ohm coax?

I would hang a 50 ohm dummy load on it at the end of the cable that goes to
the antenna and load it to the same power level you have the problem with.

Then move the dummy load to the next joint then the next joint and so on
and do the same test.

Verify and re-verify. shack and move connectors to see if it happens again.

Replace bad section.

My guess, and I have guessed wrong many times is a bad connector joint.
When this happens I replace the cabe and connectors and start all over with
new.

-- 
Jim K9TF