Re: Hamstick-40 and Autek RF-1, and the Rockloop Tuned Loop antenna

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From: JCoote@aol.com
Date: Tue Aug 01 1995 - 23:46:58 EDT


Some comments on small, tuned loops:

These antennas sometimes have extreme voltage and current nodes depending on
their Q and the RF power used. When the loop conductor is very thick, Q
goes up and bandwidth goes down. There is some material by W5QJR on the
subject in the ARRL Antenna Book which I recommend for anyone interested in
building "small" or "magnetic loops"... or to anyone who wants to know how
antennas like the AEA or MFJ loops work.

Even in a less efficient loop with a thin conductor, I wonder if RF voltage
could be arcing across the tuning cap? Also, some variable caps (especially
surplus stuff) can have very strange values (example) 80-200 pF instead of
2-200 pF. Be sure your cap really is 3-100 pF.

I wonder about the incandescant lamp in the "Rockloop". Would it's filament
add resistance or a small inductive reactance to the Rockloop, and would
removing the lamp change the antenna?

A version of the Rockloop I read about used a broadband toroid RF matching
transformer between the 50 ohm coax and loop. Another thing to check would
be the toroid. Is it the correct one? If the toroid is surplus or brand-x,
you will never know what material it is since there is no standardization for
toroid color codes.

72, Jay WB6AAM


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