Well, there's an interesting article in the latest QEX that's going to have me
up the 40 foot extension ladder again. Along with more measuring gear than I
ordinarily tote to work on an amp.
According to my 12 year old notes a ferrite balun at the feed point of a not
too unbalanced dipole will drop the current on the outside of the coax shield
to a quite reasonable value, a few ma, EVEN with my Titan working hard, so I
have been using one at the feedpoint of my VERY low dipoles for that time.
For a radically unbalanced antenna such as a windom (note uncaptalized w, a
Windom takes a single wire feeder) I pull out my Millen GDO and wind a resonant
choke balun around the body of the ferrite balun I would ordinarily use. The
antenna hooks to the choke, then through the ferrite, to the lightning
arrestors, etc.. And the measured current on the shield is very low.
Again, this has stood up without problems for over a decade, usually running
500-1,000 W and when I have a guest op over will go a full weekend at the legal
limit. No smoke, no flames, no RF in the shack, and everything works as
expected. Or does when the dogs don't chew holes in the coax and let all this
nice California sunshine in.
However, the QEX article, all computer simulation, says this is pretty much all
wet. So as soon as the rain stops and I get a chance I intend to go up the
ladder and repeat my last set of measurements. Computer simulation is fine -
but a computer simulation of a cup of coffee does not wake me up in the
morning. A jolt of real joe does.
73 Pete Allen AC5E
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