> Steve, as I understand it the issue is voltage, not current -- the induced
> voltage at the top of a shunt fed tower can reach several thousand volts
> with high power, and a surprising amount even with low power. Perhaps it
> found a way to ground through the insulation on the balun windings...
Interesting...the damage really looks like heat...it appears like the core
stack just got VERY hot.
I can't see any evidence of arcing or other high voltage effects. Unlike
some others, I have never
noticed arcing or sudden SWR changes indicating same when loading the tower
I run 1 KW. Maybe it is not the shunt feed that is the problem.
Could there be enough common mode current on 40m to generate this much heat?
I will "push" the beam during the SSB dx tests and xmit split very high in
the SSB band
with a high SWR. The yagi is tuned for around 7.030.
> Does the XM-240 use some sort of a hairpin coil to get a match to 50
> ohms? In that case, it might be a simple fix to ground the shield of the
> coax to the boom close to the feedpoint, so that the driven element's hot
> side is at the same RF potential (at 160 M) as the boom.
NO...the yagi is a 1:1 match to 50 ohms. The benefit of those small lossy
coils : (
These 40m elements will be mounted on a boom together with a shortened 80m
and my plan includes relays to ground all elements during 160m xmit.
de steve VE6WZ.