.... and, though it may not have importance at HF, any loss in the
transmission line (unless it is very cold) will add noise at the same
time that the signal is attenuated.
Once upon a time, serious consideration was given to using liquid
air (might have been Nitrogen) to cool a rather short piece of waveguide
(between feed and first receiver stage) in a really high frequency
system that was pointing out into space. Such cooling would not have
changed the attenuation a noticeable amount, but it would have improved
the SNR.
... and further: please do not think of using the
maximum-power-transfer theorem to maximize SNR. The first stage needs
to see a (small) mismatch, which might not be seen by the transmission
line.

With a low directivity antenna in the absence of close man-made
noise sources, the above issues are usually of no importance at HF and
below because the SNR is almost always (in a reasonably well designed
system) determined beyond the antenna. [Obviously, a highly directive
antenna system could dramatically affect SNR]

73 Mac N8TT
--
J. Mc Laughlin - Michigan USA
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