Topband: Shielded, Balanced Flag

[Doug Waller]

Thanks Tom for the clear "balanced vs. unbalanced" treatise.  I had planned
to ask questions about shielded Flags on down the log, but decided to it
now, while the iron is hot.  The Little Gunn desperately needs a 160M
receiving antenna breakthrough now, for use on a subdivision lot.

>>The problem with our antennas and feedlines are that they are never
>>completely perfectly balanced, or perfectly unbalanced.

My 80M hand-held shielded loop deep-nulls local stations from inside my
shack, surrounded by wires and metal.  There is an 80m vertical within 30
feet.  I can walk all around the loop, and the station remains nulled.
Every Ham should experience this!  Conversely, my hand-held Adcock array,
using bare wire for its dipoles, only nulls outdoors, and then only if I
keep away from it.  It is very sensitive to its surroundings, easily
becoming unbalanced.

>From the above I would say that my 80M shielded loop is very close to being
perfectly balanced.  A Flag antenna could be constructed from coax, the
shields of which would be open at the term. resistor, and grounded at the
feedpoint.  With some retuning, the Flag should work just as it does now,
but not be partially unbalanced by its surroundings.

The near-perfect balanced feedline for this antenna would then be two
twisted coaxes, grounded only near the receiver.  Other pattern fill-in
problems such as re-radiating verticals and transmit/receive sig feedthrough
in the rig, could be avoided by using relays to isolate the transmitter and
detune the vertical at the same time, during receive.

When enough of these 160M receive problems are solved, the way will be paved
for the fabled Rotary Beverage.  I believe the collective wisdom of the
Topband Reflectees can push this project over the top.

73, Doug / NX4D