[SECC] 160 meter antenna

David L. Thompson thompson@mindspring.com
Tue, 13 Nov 2001 21:59:58 -0500

I agree with Gary K9AY about the C antenna.   I originally called it a 1/2
wave partially vertical L but it is a 1/4 L with a 1/4 wave counterpoise.  I
used the 80 meter full size loop in the W1FB antenna notebook.   Jim West of
Antennas West ran his modeling program and feeding it at the bottom was
1.94DBi  but feeding it at the top was 4.86DBi.  I used ladderline and it
was good on 160 and I closed the loop and it worked very well on 80.   The
antenna was 90 feet horizontal with 45 feet vertical legs and the bottom leg
was 10 or 12 feet off the ground.  W1FB called it a 1/4 wave L with one
counterpoise.  I just swaped it around so I fed it at the top and used a
small relay to close the loop for 80 operation.  I tried to make it work
better on 160 by adding a couple of more counterpoises but that effectively
ended 80 meter operation.

What we did find is that antenna fed at the bottom was about 25 ohms a
somewhat inductive, but fed at the top was 9 ohms and nearly 1500 (-J) so I
needed a 200 pf cap to make it resistive.   In either configuration with
tuner you only had about 20 khz before you needed to touch up the
tuner...boy its a pain to keep adjusting a tuner during a contest.   K4SB's
version has a larger vertical section and the ends don't come too close so
probably not as inductive as the W1FB loop.

I have had 5 different 160 antennas up since 1988 and they all blew
down...guess the old adage about being too big is true except I wish they
would perform better....its hard on a 1/2 acre lot!

73 Dave K4JRB

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