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For 7.0 MHz,
the lengths of the two 3/8 wavelength feedline sections should be about
34.8 feet with polyethylene dielectric coax (velocity factor .66) such as
RG-58, RG-8, and RG-213. For foam dielectric coax such as RG-8X (velocity
factor .81) the best length is 42.7 feet. This affects gain and directivity
but is probably not highly critical. For mid-band, 7.15 MHz, the
respective lengths are 34.0 feet and 41.8 feet.
Note that the Ameritron RCS-8V does not
switch both the center conductor *and* the braid of the coax,
as stated by K4TX. (Perhaps he meant that any unselected HOT [center] conductors are not grounded by the switch?) All connector shells are grounded to
a common point on the circuit board, according to a schematic which I have seen. He does report that his
antenna works very well, however.
Regular coax switches probably should not be used
with this antenna.
You might want to build your own remote switch box
for this antenna switching scheme- one that switches the braids as well.
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This is an interesting version of the ever popular 40 meter delta loop
beam that was built by
K4TX/K4GE.
It is quite effective for a relatively simple wire array.
Two things contribute to its top notch performance- the clever use of
3/8 wavelength feedline sections to tune the non-driven loop as a
reflector (as seen on the K3LR 160m sloper array),
and the 'upside-down' configuration with the point of the
delta at the bottom. This increases the effective height of the antenna
over the more commonly used point-up configuration. The antenna has good
F/S rejection and around 10-15dB F/B, which can make all the difference
between hearing or not hearing weak DX signals on a noisy band.
