Topband: electric fences and Beverage termination
btippett at alum.mit.edu
Wed Dec 28 11:58:49 EST 2005
>As for the proper resistance on a Beverage termination, you are
looking to maximize front to back. Bill Pfaff, K2GNC wrote an article
on how to find the "right" resistance in one of the ham magazines (I
googled him but couldn't find it but I think it was HR) where he
attached a carbon pot to a kitchen timer and then set it to one hour.
He tuned a station off the back of the antenna and then waited for
the corresponding best F/B by time. He reset the time to the best F/B
and then measured the resistance. He then got a fixed value carbon
resistor and used that value for his antenna.
Craig this is a waste of time. When you tune
for best F/B to a point signal, you are only putting a null
on that exact azimuth and elevation angle. This really does
nothing for the overall RDF or DMF of the array. Unless your
QRM is always from the exact same point as your test signal,
the F/B will not be the same. ON4UN comments on this in
Chapter 7, Paragraph 2.5 in his new book.
The best method is as W8JI described...tune for
flat SWR (1:1 is not necessary) over the frequency range of
interest. This is one application where the AEA HF-CIA
really shines. You can sweep the frequency range of interest
and simply adjust the termination for the flattest response
on the swept SWR display.
73 & HNY to all!
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