[Elecraft] K2 Alignment with Spectrogram

[Jim Faulkner]

My K2 S/N 5149 has been up and running well for about 5 years. I finally
decided to check out the filter alignment using Spectrogram. I
downloaded v.16, and am running it through Wine since I'm using Ubuntu
as an operating system. I couldn't get the version on Tom's page to run
this way, and right now, I don't have easy access to a Windows machine.

The parameters on the newer version are a bit different than what Tom
specifies: 
1. The slowest sampling rate is 22K, probably not a problem;
2.  To get a 10.8Hz frequency resolution, I need to set the FFT size to
2048 (1024 gives a default of 21.5Hz), again probably not a problem, I
can probably even go to a higher rate and get fewer artifacts on the
signal;
3. Band limits set from 0 to 2840Hz.

I'm using the K2's headphone output to connect to the mic input on the
sound card. Its settings are minimal, but I have selected the correct
input, and am not adding any amplification. The program does appear to
work. I can see the different filter widths, and can move them about the
600Hz cursor to center them. 

There is a lot of noise riding on the signal, maybe "5dB-10dB" worth.
There is a Peak Hold function that shows a reasonable shape to the pass
band if I engage it, but the live signal is very noisy. Also, instead of
being way down in power, like in Tom's example, to get the baseline of
the signal at the bottom, I had to set the spectrum level from -10dB to
60dB (This may be a function of my sound card (?)).

I attempted the L34 alignment as also mentioned in Tom's instructions,
and that's where the questions really started. The noise level riding on
the signal is the same, and there are spikes at 600Hz intervals. The
first (@ 600Hz) is about 20dB-25dB above the noisy baseline. The problem
here is that L34 is maxed out up. If I adjust it down, the spikes do
start to descend into the noise. I am worried that there is a problem
with L34, or another component in that circuit that isn't allowing
complete adjustment, and causing the noise riding on the signal. I did
do this by ear, per the manual, and the tone at 7Mhz did get louder, and
the noise did subside, but Tom's comments in the instructions lead me to
believe that there should be enough adjustment in L34 to clean up a lot
of the trash on the signal.

Is there a problem, or am I over-analyzing this, and is the ability to
center the pass bands all that matters? Any comments/criticisms are
welcome. 

Thanks in advance. Jim KO5V
Sandia Park, NM