[Elecraft] Re: K3 receiver sensitivity on 50MHz

[Bill W5WVO]

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