[Elecraft] K3 and Preamp

[Edward R Cole]

Maybe most of you already know this, but...

It has been accepted that the K3 receiver needs a little help of a 
preamp on 10m and 6m (especially 6m).  That is why Elecraft came out 
with the PR6 and later the PR6-10 preamps.

At lower frequencies the level of sky noise is much higher which 
overwhelms any noise generated internally by the receiver, thus a 
preamp would only contribute gain making both noise and signal 
louder.  But around 30-MHz sky noise  starts dropping so that it is 
necessary for the first stage of a receiver to be "quieter" 
(technically that is called a low noise figure).  If the noise 
generated in the receiver is significantly equal to sky noise the 
receiver sensitivity is not optimum (meaning you can't copy weak 
signals).  This trend continues downward with increase of frequency 
up to 1.2 GHz where sky noise is minimum (on earth).  One cannot 
receive "weaker" signals without a low-noise preamp close to the antenna at mw.

So, use of the internal preamp is generally not needed below 20m as 
all it will do is increase noise volume and not improve receiver 
sensitivity.  But at 15m it often helps.  At 10m the internal preamp 
is inadequate to obtain maximum sensitivity and an external low-noise 
(figure) preamp can really help.

Like I said at the beginning, maybe you already knew this...

73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
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