wayne burdick wrote:
I should mention that the operator would be able to turn the K3's regular
preamp off when using the external preamp, if desired (and/or turn on the
attenuator). Thus there would be a full range of possible NF/dynamic range
tradeoffs under convenient operator control.
This capability is especially advantageous for 6M work because of the
prevalence of sporadic-E propagation on this band. When the E-skip is running
hot during a summer contest, propagated signals equaling or even exceeding the
strength of local stations are commonplace, and that rather big band can get
VERY crowded very quickly. The tremendous strength of these signals is due in
large measure to the very efficient nature of sporadic-E ionization. Formed by
high-energy wind shear layers, sporadic-E clouds are very planar, and are
therefore in general more efficient reflectors than the more loosely
structured F2 layer. In addition, they are closer to the Earth, so there is
less relative path loss. Finally, 6M antenna systems are oftentimes "larger"
in terms of ERP than a system of equivalent cost on HF. It all adds up to
extremely strong signals.
But if you live well out into the countryside, away from the man-made RF
racket of the towns and cities, 6M can be a very quiet band, much quieter than
on 30 MHz and below. (I wish I lived far enough out in the boonies to be able
to hear my receiver's noise floor with the antenna connected!)
IMO, due to the combined effect of all these factors, 6M arguably demands the
highest flexibility in receive dynamic range vs. sensitivity of any amateur
band.
Bill / W5WVO
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