[Elecraft] K3 Sensitivity

[brian]

Jay,

As promised, I went ahead and measured my K3 sensitivity.  It is really 
a K3S-.  It doesn't have the USB I/O board but has the rest of the K3 -> 
K3S upgrades.  There general coverage bandpass filter board is installed.

Here are the results on 20-6M.

The sensitivities are as expected and comparable to other rigs' 
published results.  They also seem to agree reasonably well with more 
well equipped lab K3 results.  I don't claim well equipped lab accuracy.

Condx:
1) SubRX off, attenuator off
2) CW mode
3) 400 Hz filter in
4) Measured the S/N with Spectrogram.  These numbers are based upon a 10 
db S/N ratio.  That also happens to be the MDS I can hear +/- a few dB.

On the 12,10,6M bands a 20 db S/N was measured and then subtracted 10 dB 
from the result.  This is to eliminate possible signal generator leakage 
effects. The K3 audio output is very linear with RF signal level input 
so this is a reasonable thing to do.

BAND  no preamp   preamp1   preamp2
20    -144 dBm      -147       x
17    -143          -145       x
15    -143          -147       x
12    -144          -144      -154
10    -143          -145      -156
6     -136          -141      -151

I'm not sure I believe the -15x numbers.  Elecraft does say preamp 2 is 
ultra low noise.

Measurement setup:
HP-8657B signal generator with additional internal shielding.
20 db attenuator at the generator output.
double shielded RG-400 coax to K3 antenna.
HP-8657B output verified with an HP-3586C up to 30 MHz down to -122 dBm.
Spectrogram on a Delta 44 sound card to measure S/N.
Signal measured from K3 line out.

YMMV

73 de Brian/K3KO

P.S. Switching in the second RX reduces these numbers about 3 dB.

On 1/29/2017 3:55 AM, jay Miller wrote:
> I assembled my K3/100 with the second receiver in December of 2010.  The
> weak signal performance was much better than my original IC-756 rig. I did
> not install the automatic antenna tuner.  I have continued to download the
> software changes since then.
>
>
>
> Two years ago I installed the general coverage receiver modification.  I
> thought it was my imagination at the time but I thought had experienced a
> slight decrease in the primary and secondary receiver sensitivity.
>
>
>
> Today I put my Kenwood TS-480 that I had been using as a mobile in the
> shack.  I was listing to a couple of weak strength SSB QSOs using the K3.
> Out of curiosity I switched over to the TS-480 and was surprised that the
> weak signals were more "copy-able" on the inexpensive Kenwood than on the
> K3.  Does this indicate a problem with the RX in the K3 or is the apparent
> difference in the TS-480 RF gain come at the price of the definitely poorer
> adjacent signal rejection?
>
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