[Elecraft] K3 6/10M pre-amp

[Edward R Cole]

To respond to Scott's comment:

My experience is that the K3 with internal preamp (PRE on) is not 
able to hear weak signals as well as the KX3  (with its preamp set to 
30-dB gain).  This is an accepted condition by Elecraft and they 
responded by providing the PR6 and now expanded this to 10-12m with the PR6-10.

I suspect (but have no technical evidence) that maybe the K3 is too 
low in overall system gain at 6m.  The PR6 or other external preamps 
provide this (plus lowering system NF).

MDS is good alternative to noise figure (NF) measurements.  The PR6 
is cited by Elecraft providing -143 dBm sensitivity at bw=500 Hz.  NF 
claim is 0.7 dB with 0.5 typical; PR6 gain = 18 dB.

The K3 is cited at MDS of -136 dBm at bw=500 Hz.  This is adequate 
information for calculating equivalent NF.  -136 dBm is equivalent to 
a NF =11 dB at bw =500 Hz into a 290K termination.  Adding the PR6 
brings this down to -145.6 dBm.  Pretty close to what Elecraft claims.

My measurements were with bw=2.8 KHz (-130 dBm), so correcting for 
bw:  10Log(2.8/0.5) = 7.5 dB this would result in -137.5 dBm 
MDS.  Considering I am doing this by ear it comes pretty close to the 
Elecraft spec for the K3 with internal preamp.  What was a surprise 
is the KX3 observed MDS was 3-dB worse than the K3 at -127 dBm 
(-134.5 dBm corrected for bw).

My measurements do not match on-air experience??  Only conclusion is 
that the test set up is not providing a stable output.  XG3 is a 
great tool for checking performance but maybe sensitive to loading 
(just guessing).  Probably the best I can achieve with equipment at 
hand.  Hope the math was entertaining - HI.

73, Ed - KL7UW


---------------------------------
From: Scott Manthe <scott.manthe at gmail.com>
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] K3 6/10M pre-amp
Message-ID: <51DB39CE.6080001 at gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Maybe the signals are louder on the KX3, which would fool people into
thinking it was more sensitive? I've always thought my K3 was adequate
on 6 meters. Not gangbusters, but certainly adequate.

73,
Scott, N9AA


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