I just finished helping a friend raise a Pro 57 yagi. When I looked it
over, I noticed that it had a split driven element and was fed thru a
coax balun. However, there was an aluminum strap connecting one side of
the driven element to the boom. This is the side attached to the coax
shield terminal of the balun. The driven element is actually a 2 el log
cell. I thought he had made a mistake in assembling the antenna but when
we checked the instructions, that is what they said to do. I have great
difficulty accepting this as proper design. It seems to me that part of
the transmitted power is applied to the boom as well as one half of the
driven element. If it were mine I would have cut the grounding strap and
operated the log cell driver in the usual manner. I suppose one could
argue that it is desirable to have a driver grounded for lightening
protection? Is it possible that the designers have measured the
impedance presented to the driven element by the boom and it is high so
will not take any current when connected to one side of the feed point?
Does anyone have a rational explanation for such an unorthodox drive
system?
73, Dan, N5AR
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