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Old December 4th 05, 06:57 AM posted to rec.radio.amateur.antenna
Roy Lewallen
 
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Default Antenna reception theory

Reg Edwards wrote:
Thank you Roy.

I don't doubt that your answer conforms to the learned text books on
the subject. But I am suspicious the text books may be wrong.

I will do some calculations related to radiation resistance and power
available to a matched receiver. If I think my suspicions are correct
then I will come back to you.
----
Reg.


To tell the truth, I got the result for a wire over ground from an NEC-2
model, after first checking to make sure I got the theoretical 0.5 volt
for the center of a dipole in free space. (NEC-2 has provision for
applying a plane wave to the model.)

In the process of confirming the 0.5 volt value, I found an error in a
popular text, Balanis, _Antenna Theory, Analysis and Design_. On p. 61,
he incorrectly states that the current along a short dipole "can be
assumed to be constant", which isn't true, and from that concludes that
the "induced voltage" would be 1 volt when the dipole feedpoint is short
circuited. How he defines "induced voltage" with a shorted feepoint
isn't clear, but the uniform current assumption he used to get it is
incorrect.

Kraus, in _Antennas_, and others get it right, and modeling confirms it.

Roy Lewallen, W7EL
 
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