February 25th 06, 03:49 AM
posted to rec.radio.amateur.antenna
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80 m compact loop - progress report
Frank,
Will you please forward the nec code?
Thanks - Dan
Frank's wrote:
This winter I have been working on the design and construction of a
compact loop for 80 meters. The loop will be constructed from 72 ft of
3/4 in copper pipe and will be in the shape of an octagon. The plane of
the loop will be vertical, and the loop will be remotely tuned by a
vacuum variable capacitor coupled to a geared stepper motor.
I have just finished constructing and testing the driver for the stepper
motor. See
http://tinyurl.com/bwobb for pictures and some information about the
system. Constructive comments will be appreciated.
John, N9JG
John, how high above ground is the antenna?
Frank, VE6CB
John, just for interest I placed the top of the antenna at 30 ft; which puts
the base at about 8' 3". Using NEC's Sommerfeld/Norton ground with: sigma =
5 mS/m, and Er = 13. The input impedance computes to 6.57 + j855.6 ohms.
Since this is very close to the edge of the Smith Chart, your 1 ohm figure
is probably within a reasonable margin of error. However I cannot see how
you can match such an impedance with a single element.
The structure appears to be a very efficient, physically small, antenna.
NEC computes 0.84% copper loss.
Frank
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