A 2L Delta Loop makes a simple effective antenna.
I used one on 40M, suspended from a 20 ft boom
mounted at 120 ft on a tower leg with pulleys at each
end and a continuous rope through them to allow me
to attach the loops at the tower and pull them out to
the ends. Small ropes can be used to pull out the
corners. Feed impedance is approximately 100 ohms
which is easily matched to 50 ohms with 1/4 wavelength
of 75 ohm coax (RG59). It was a KILLER antenna.
Quads and Delta Loops work better with reflectors.
You could use a common reflector with separate
driven elements on each side to make a reversible
pattern. OR, you could use a 3/8 wavelength length
of coax to a pair of relay contacts (switch both sides
of the coax). Each element would be identical, cut
for resonance in the band. The unfed element looks
like a reflector because the unfed stub presents an
inductive reactance at the feedpoint. For matching,
you would need 1/4 WL of 75 ohm cable plus 1/8 WL
of 50 ohm followed by 50 ohm to the transmitter. OR,
you could just use 75 ohm cable for the whole length,
as long as it is cut to an odd multiple of 1/4 WL (electrical).
73 / GL, Tom N4KG
BTW, the TOWERTALK reflector would be a better place
to post antenna / tower / rotor questions. To subscribe,
send message with "subscribe" in the text to
towertalk-request@contesting.com
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