Rod -
The GAP antennas use inductive loading on the lowest band which reduces
efficiency on that band. This inductance is in series with the
feedpoint. It
is derived by using a capacitor transformed through a piece of coaxial
transmission line to provide an inductive reactance at the lowest
frequency.
(See the GAP product review in January 1995 QST by K5FUV).
Another effective and low cost alternative is to use TWO antennas, one
for the low bands and another for the high bands.
Specifically, the MFJ-1792(?) 80/40 or the 80/40/20 version.
This antenna is full size on 40 meters and has a 40M trap plus capacity
hat for effective top loading on 80M. The 80/40/20 version has a 20M
element supported parallel to the 40M section. This could be converted
to 30M with no problem. It does require a good radial field under it.
For the high bands, the R5 makes a fairly low cost and efficient
solution.
A really low cost solution would be to hang a 20M dipole vertically from
a non-conductive support (i.e. tree) and feed with ladder-line. This
would
work as a half wave vertical dipole on 20M, two half waves in phase on
10M
and something inbetween on 12/15/17 meters. I use just such an antenna
as a 5 band horizontal dipole at 50 ft with good results.
de TOM - N4KG
.
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