[Elecraft] K3 6/10M pre-amp

[Wayne Burdick]

Typical KX3 MDS with preamp on is about -138 to -140 dBm in a 500-Hz bandwidth, on all bands. 

If a KX3 is measuring -134 dBm MDS in this bandwidth, chances are there's a measurement error, or the ATU has been left in-line at an impedance other than that of the source RF generator, etc.

73,
Wayne
N6KR


On Jul 9, 2013, at 9:15 AM, Edward R Cole <kl7uw at acsalaska.net> wrote:

> 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" 
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