http://ham-radio.com/k6sti/broad.htm
The writeup describes a simple upgrade for an FM broadcast receiving
antenna, but the idea may have application at HF. For example, if you
hang a quarter-wave wire from a tree 90 feet away from a quarter-wave
40-meter vertical, you'll get 3 dB gain in two directions. The wire will
need radials or a good ground connection, but it will not need to be fed
nor must the vertical be rematched. The half-wave 40-meter wire vertical
I once used in a tall Eucalyptus tree would need only a parallel wire.
Due to the height needed when used with a horizontally polarized
antenna, I think a parasitic broadside element is best applied to
vertical antennas at HF.
A director can provide higher gain, but the array will have low
impedance, require antenna rematching, have restricted bandwidth, and
may have higher ground losses. A detuned reflector can provide about the
same gain as a broadside parasitic element when placed 46 feet away from
a 40-meter vertical. Impedance is high enough that you can get away
without rematching. Response is unidirectional with low F/B. This gives
another antenna upgrade option, depending on available supports.
A broadside parasitic element or a detuned reflector are quick and easy
antenna upgrades. They're not something you'd design from scratch.
Feeding both broadside elements will yield higher gain, as will properly
tuning and matching an end-fire parasitic array.
In 30 years of antenna modeling, this is only the second design that has
surprised me. The first is here: http://ham-radio.com/k6sti/tilted.htm.
I stumbled across both while modeling something else. I like to pass
along unexpected results. You never know when an antenna trick may prove
useful.
I subscribed to Towertalk only to post this message. I'll unsubscribe
when I see it appear. If you have a question, contact me by email at the
address given in the writeup.
Brian
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