[Elecraft] K2 CW Filter Loss

[Lemkes]

I keep forgetting to use "Plain Text":
Don,
  Thanks for the analysis.  I will send you the Spectrogram plots.  We have 
family visiting this weekend, but I can get back to the K2 on Sunday evening 
or on Monday.
  I did look at the 1 microvolt signal with Spectrogram.  As I remember, the 
peak did indeed not drop with narrowing bandwidths, which I thought curious 
(but didn't pursue).  The noise level was pushed down off the bottom of the 
display, so I'll have to adjust the scale to get it all back on the screen.
  When performing the MDS measurement using a DVM on AC volts at the phone 
jack I get:
       OP1 2.4 kHz   S+N= 3.15 VAC       N=0.1 VAC
         F1  1.2 kHz   S+N= 1.14 VAC       N=0.065 VAC
        F2  0.80kHz   S+N= 0.80 VAC       N=0.060
        F3  0.40kHz   S+N= 0.535 VAC      N=0.057
So, I am running into a "noise floor" that seems to be coming from a 
combination of the product detector/mixer and the audio amp.  When I use the 
built-in amplification in the DSP or use an external audio amp, I can gain 
another couple dBm of MDS across all bandwidths.  Oh, the Preamp is on, and 
the AGC is off.  RF gain full on, and audio gain at least at 3 PM to full 
on, no load on the phone jack other than the DVM.
  The Spectrogram plots should be more revealing.  Vic, K2VCO also suggested 
(as you did earlier) that I take a hard look at T7.
  More later.  73, Dick, AD7AF

Dick and Marty Lemke
PO Box 1038
Ocean Park, WA 98640
Tel. 360-665-2438
www.lemkestudios.com