Topband: W6SAI three wire inverted L

[Tom Rauch]

I am about to erect an antenna for Top Band,  I've found an
article on the Web from an old issue of Ham Radio magazine,
where W6SAI described the evolution of a 3 wire inverted L
for use in a small garden/city lot.   The antenna is based
on a 135 foot (35 up 100 out) inverted L,  this single wire
antenna was adapted to use 300 ohm ribbon, and then to a
system with three wires with the centre conductor going to
the transmitter and the outer two being connected to ground
at the feedpoint.
The claim is that using this system the efficiency of the
antenna was raised to over 80 %>>

Bill was wrong. He admitted to me in private conversation
his idea was wrong but I never saw a coreection in his
Handbooks or in magazines. Several years ago when speaking
to Roy Lewallen W7EL,  Roy mentioned a similar story. He
said Bill did the same with him, when he questioned Bill on
it.

I have to admit to "knowing enough theory to be dangerous",
and it may well be that the much missed W6SAI was correct,
my gut feeling is that this may be another occasion where
feedpoint impedance is translated to radiation resistance -
can any of you who understand the physics and especially the
math please tell me whether I'd be wasting a lot of time and
effort making up the spreaders etc for such an aerial with
respect to a single-wire Inverted L?>>

Sure. It's nonsense. The RSGB even pulled that stuff from
it's books.

The sum of currents from ALL the wires enter the ground. The
feedline moves to one wire. This means the feedline sees and
increase in impedance, but the ground sees almost exactly
the same current. Nothing changes.

See:
http://www.w8ji.com/radiation_resistance.htm

And finally, I tried a rather novel Top Band antenna last
Winter KE4UYPs  "Top fed linear loaded" dipole arrangement
with 132feet out and 170 feet of linear loading in the other
leg at two foot intervals, this enabled me to span the
"pond" with 80W and increase my country score quite well,
the downside of this antenna is that if like many of us you
share the Antenna space with the XYL who for some strange
reason considers that plants should be grown etc, that you
can have a real problem with the up and downs of the linear
loaded bit... but I mention this as it may be an antenna
worth trying for those without the space to erect a full
sized Top Band dipole.>>>

The most efficient way to load an antenna is with
capacitance at the open ends. As for lumped loading inside
the length of the element, a conventional coil actually has
less loss than linear loading when wire sizes are remotely
simila and the coil has even the most reasonable form
factor. Linear loading is largely something antenna
manufacturers hyped all out of proportion as a sales pitch.
Typical Q of linear loading is in the low multiples of tens.
Typical Q of a modest inductor is in the hundreds. A coil
has about 1/10th the loss resistance for a similar
reactance.

73 Tom