In article , "Wes Stewart"
wrote:

Antennas are reciprocal, if they wouldn't work well for transmitting,
they will work equally poorly for receiving.

The reciprocity principle is usually good physics (but watch out for
Faraday rotation). However, the engineering virtues of a good transmitting
and good receiving antenna are different. At HF and below, efficiency is
much less important for receiving than it is for transmitting. The reason
is that the natural noise level is high at these frequencies: at 10 MHz
it's 30 dB above thermal, while a good receiver's noise floor is 10 dB
above thermal. This leaves plenty of room for inefficiency without SNR
degradation. At lower frequencies the natural noise is higher. In practice
10 meters of untuned inverted L into a 500 ohm input suffices to reach the
natural noise floor from 100 kHz to 30 MHz with a good receiver.

Back in the days of the omega navigation system, we used tuned 2 meter
whips to receive signals from around the world in the 10 kHz band.

For the results of quantitative engineering calculations on this subject,
see:

http://anarc.org/naswa/badx/antennas/SWL_longwire.html

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| John Doty "You can't confuse me, that's my job."
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