I am planning on using a 45ft vertical during the CQ 160 CW contest
next week:
http://www.dellroy.com/W4EF's-Ham-Radio-Page/Stew-Perry_El-Mirage/El-Mirage.
htm
The configuration shown in the picture uses four 20ft top hat wires
sloping down at 45 degrees. According to EZNEC the system is
resonant at ~2.7 MHz. At 1.8 MHz the real part of the base resistance
is about 7 ohms. The pros of this configuration are that it is real easy
to put this antenna up (takes about an hour at a fairly leisurely pace
plus however much time is needed to lay ground radials). The
downside is that it is electrically short which makes it a lossy match
with my T network tuner. Tuner components also arced above about
600 watts presumeably due to the very high reactance of the antennas
input impedance.
The alternative is to take along a 36 ft Rohn push-up mast lash it to
the RV trailer were taking and put up an inverted L (45ft vertical, ~90
feet horizontal). This configuration would have a base impedance of
about 13 ohms resistive which should make for a more efficient match
using the T-network. Also, the higher base resistance should result in
overall better efficiency. The downside is of course the extra hassle
of putting up the 2nd mast. Since I am planning to install some
RX antennas, I will have my hands getting all the hardware installed
in the time available. Anything I can do to shave off the workload is
desireable, so I am trying to figure out how many dB's that inverted-L
will be worth over the top-loaded vertical. The antenna will be installed
over the sand along a salt water beach with about twenty 100ft long
radials under it.
Any thoughts on whether the inverted-L is worth the extra work of
installing a second mast?
Thanks,
Mike, W4EF........................................
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