Re: CURIOUS ANT QUESTION

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From: wkhibbert@juno.com
Date: Thu Apr 03 2003 - 08:30:00 CST


Hi Joel. Keith here in the Depths of the Great Bergen Swamp

Here's some info I found for your antenna question:

-----------< dipole_array.txt >------------------

Phased Horizontal Arrays

Source: The ARRL Antenna
Book, 14th Edition,
Chapter 8, Page 8-11

"Phased arrays with horizontal elements can be
used to advantage at 7 MHz, if they can be
placed at least 40 feet above ground. Any of
the usual combinations will be effective. If
a bidirectional characteristic is desired, the
W8JK type of array is a good one. If a
unidirectional characteristic is required,two
elements can be mounted about 20 feet apart
and provisions included for tuning one of the
elements as either a director or reflector.

The parasitic element is tuned at the end of
its feed line with a series- or parallel-tuned
circuit (whichever would normally be required
to couple power into the line), and the proper
tuning conditions can be found by using the
system for receiving and listening to distant
stations along the line of maximum radiation
of the antenna. Tuning the feeder to the
parasitic element will peak the signal."

The ARRL Antenna Book also included a diagram
showing either the classic W8JK feed (crossed-
over open wire line between the dipoles, fed in
the middle of the crossover section) with a
spacing of 16 feet between the dipoles and two
paralleled dipoles spaced 20 feet apart with
open wire (or balanced line) going to the
station from each dipole. One of the dipoles
is labelled "Parasitic" and the other is
labelled "Driven"

According to the text on the illustration,
"The length of the elements in either antenna
should be exactly the same, but any length
from 60 to 150 feet can be used. If the
length of the antenna at A (the W8JK) is
between 60 and 80 feet, the antenna will be
bidirectional along the same line on both 7
and 14 MHz. The system at B (the parasitic
dipole array), can be made to work on 7 and
14 MHz in the same way, by keeping the length
between 60 and 80 feet."

eof

So, with a couple of trees in the right spot, some twin lead, wire and
time you could have a dual-band directional array. At QRP levels, a
receive rated variable cap would handle the tuned circuit duties and will
a suitable arrangement you could quickly retune o 20 an 40 Meters. I
don't see why it would not work on 30 Meters also, but 30 Meters was not
a ham band at the time the edition of the Antenna Book I have was
printed.

Have fun and let us know how it works out.

73, Wm. Keith Hibbert, WB2VUO, TC/WNY ARRL Section
President, Brockport Amateur Radio Klub
"My night light runs more power than my Rig!!!"

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