[Elecraft] K3s noise figure spec

[Edward R Cole]

Dave,

I don't know the NF, but my K3 with PR6 (which the K3s supposedly has 
internal) has a MDS of -145 dBm at 500-Hz bandwidth.  That is fine 
for 50-MHz on eme (most demanding mode).  I have a ARR P50VDG preamp 
at the base of my 6m-eme tower which provides 0.5 dBNF with 24 dB 
gain.  I run it with PR6 turned off for very slight improvement.

The K3s 50-MHz NF is probably fine with internal preamp ON.  For 
comparison my 2m-eme system MDS is -157 dBm (preamp is 0.1 
dBNF).  But on 144-MHz low NF has more benefit since sky noise is 
lower (250K vs 2000K on 6m).  In truth with the rise in environmental 
noise, low NF on 2m is getting less effective.

6m-eme folk say this:  "If your coax line loss to the antenna is < 1 
dB, locating a preamp at the antenna is unnecessary".

K3s should do fine without external preamp (in general).

BTW my KX3 with internal preamp at 30-dB gain level has equal 
sensitivity to my K3+PR6.

73, Ed - KL7UW

Date: Tue, 30 Jun 2020 19:31:01 -0400
From: Dave Sublette <k4to.dave at gmail.com>
To: Elecraft Discussion List <elecraft at mailman.qth.net>
Subject: [Elecraft] K3s noise figure spec

Does anybody KNOW what the noise figure is for the 50MHz preamp on the
K3s?  It isn't listed in the specifications.

I need to know in order to make system noise figure calculations.  My
feedline is going to be long (low loss, but long) and I'm trying to
determine if I will need a preamp mounted at the antenna.

Thanks,

Dave, K4TO


73, Ed - KL7UW
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