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Old April 26th 07, 05:37 PM posted to rec.radio.amateur.antenna
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Default Measuring Antenna Efficiency

Art wrote:
"I have determined that coupling of elements which means parasitic
elements is wasteful."

A parasitic element is normally constructed of low-loss material and
re-radiates all the energy it absorbs from the radio wave. If it is
placed and phased right it can reinforce radiation in the desired
direction.

Kraus in the 3rd edition of "Antennas" has his close-spaced all-driven
W8JK array and a wide-spaced all-driven 2-dipole array in the same
figure, Fig. 6-12, on page 184. The gain of either antenna is about 6
dB, supposedly with respect to an isotropic, or about 4 dB with respect
to a dipole. Both arrays are bidirectional.

Arnold Bailey catalogs a version of the W8JK close-spaced all-driven
array on page 511 of "TV and Other Receiving Antennas". On page 516 is a
1/2-wave radiator with a 1/2-wave parasitic reflector 1/4-wave behind it
(a simple Yagi).

Bailey gives the W8JK a resistance of 7 ohms and a gain of 4 dBd (6
dBi).

Bailey gives the parasitic array a resistance of 28 ohms and a gain of 5
dBd 7dBi). The parasitic array is slightly unidirectional while the
pattern of the W8JK is symmetrical.

Best regards, Richard Harrison, KB5WZI

 
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