[Elecraft] Low sensitivity on K2...

[Don Wilhelm]

Robin,

What filter were you using when doing the sensitivity measurements?  Did 
you use the same filter width for each?
If they both have the KSB2 installed, try doing a comparison with the 
OP1 filter selected.

Is one K2 above SN 3000 and the other below 3000?  If so,  yes there may 
be differences.  The very early K2s had a winding ratio of 13:4 on T7 
while the newer ones use a 20:5 ratio - that will account for about a 3 
dB difference.    The early K2s IF crystals did not make a consistent 
filter as the newer crystals.  The newer crystals are installed in all 
K2s above SN 2560.  There may be differences in the AGC settings that 
will change the apparent response - turn AGC off when making similar checks.

There can be significant differences introduced by the filter 
alignment.  I suggest using Spectrogram  (or Spectrum Lab or other audio 
spectrum analyzer) to look at the filter shape and the output level - dB 
above the noise floor makes a good comparison, while raw signal 
amplitude does not compare well because the AF Gain will not be set the 
same.

The K2 Dial Calibration article on my website www.w3fpr.com has 
information about setting the K2 filters if you are not familiar with 
all the steps involved.

If the above does not resolve it for you, you may have to build up the 
crystal oscillator shown in the Troubleshooting section of the manual 
and do Receive Signal Tracing on both K2s to find where the difference 
is coming from.

73,
Don W3FPR


On 2/26/2012 11:51 AM, Robin Kiszka wrote:
> I have two K2s, and I find on one of them that the sensitivity is much lower.
> I see this when doing a test with an XG1 signal generator.
>
> The problem is that the "low sensitivity" rig is one that I bought built,
> while the one that works fine is a rig I built myself. I have tried to
> reallign the rig, but without much improvement to say the least. It just
> seems that AF gain is far more responsive on my own built rig, and this is
> accross all bands.
>