> How many of you operate topband with small antennas?
I did at one time though my Inv L today seems like it's a dwarf among
the contesting giants.
I was in a condo with all the restrictions you might expect. I did
put some upper band antennae tacked to the ceiling but what to do for
80 & 160... I don't recall which arrl handbook it was in but there
was a guide to shortened loop antennae made of copper pipe in a
hexagonal shape. (Essentially the same concept as the MFJ loop
antenna for the higher bands).
I made mine out of 1" copper pipe and it was 8' high and was attached
to the wall. Center conductor went to the a piece of refrigeration
copper tubing which was soldered to midway on the first 45 degree
leg. The Q is extremely high and on the 160, the bandwidth is about
3KHz at best. To change frequency you change the capacitor setting at
the feed point. A 100 watt transceiver can use an air variable but to
use power, I was using a SB-220 so a vac variable was required.
I used a pair of servos to control the vacuum variable and that
antenna would cover 160 & 80, almost up to 40M. As the Q was so high,
you really didn't need a SWR meter, you would adjust the vac variable
till you heard signal and then fine tuned the rig for the max volume.
When transmitting, it was a 1:1 and the effect of that high Q was
like a marvelous roofing filter as anything adjacent to you would
simply not be possibly able to be heard.
According to the article in the handbook, at resonance, it is
supposed to be 95% the efficiency of a dipole.
As I did use this antenna for several years I can tell you it does
indeed work but I really did need the amp to make the pileup
contacts.
Gary
KA1J
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