Re: NEC-LIST: loop antenna using the GA and GR cards

Good day all.

Harking back to the days when we had problems with NEC2 and low
frequencies for small structures ...

In 1992 one of my final year project students made a loop antenna as a
prototype for NVI HF comms on vehicles. The rectangular loop was made
of 111 mm Al tubing, and was 950 X 1600 mm outside measurements. In
one of the longer sides we left a gap, and across the gap we placed a
tuning capacitor. The loop was fed at a corner near the capacitor
using a much smaller loop with a direct coaxial feed.

Estimated efficiency was about 15% at 3 MHz, rising to about 80% at 8
and 90% at 10 MHz. Radiation resistance was of the order 10^-3 to 5
10^-1 ohms. Bandwidth was naturally very small. Using a 2:1 VSWR we
obtained the following bandwidths in measurements

B Freq
6kHz at 2,9 MHz
13 kHz at 4 MHz
40kHz at 7 MHz
82 kHz at 10,06 MHz
156 kHz at 11,6 MHz

In order to test the antenna operationally, we had our University's
radio amateur club evaluate it. Successful contacts were made with
other radio amateurs at 7 MHz over distances ranging from 80 to 1600
km. Maximum input power was limited by the capacitor, but we did
manage to run at 250 W CW.

Hope this is of interest to someone out there trying to model/build
loop antennas.

best regards,
Duncan Baker.

--
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Prof. Duncan C. Baker (Pr. Eng., FIEEE, FSAIEE, Sci. Nat.)
Dept. of Electrical and Electronic Eng.,
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