[Elecraft] K2 MixW filter alignment question

[Don Wilhelm]

Andy,

Adjust the BFO for FL4.

Use noise (a wideband noise generator, an 'antenna' wire tossed over a
flourescent lamp, or dead band noise) as input to the K2.

Connect the audio output of the K2 to the computer running MixW,
Spectrogram, or whichever program you want to use as an audio spectrum
analyzer.  You should see the filter passband on your computer display.

Enter the K2 menu for CAL FIL, then tap the DISPLAY button.  That will show
you the BFO frequency and you can tune the BFO with the main tuning knob.
Set the BFO so that the peak of the filter is set at the audio frequency
that you want to hear - normally your selected sidetone pitch.

That is all there is to it.  While you have things set up, you may want to
check all the filters too.
If you are looking at the SSB filters (or other wide filters) you may want
to view the line display rather than a waterfall pattern (I just find the
waterfall does not have enough definition for wide filters).  Two things are
important with the wide filters:
1) To preserve 'single signal' reception, the passband should not cross
'zero frequency' - actually go into the opposite sideband.  (the analyzer
display will not show this condition - look for the filter skirt decreasing
in amplitude on the low frequency side).
2) For voice reception, the filter passband should contain the frequencies
you want to demodulate.  i.e. for a 2000 kHz wide filter, the low frequency
corner of the passband should be about 300 Hz and 2300 Hz at the high
frequency corner.

Good luck.
73,
Don W3FPR

----- Original Message -----
From: "Andy Bullington" <abullington@comcast.net>
To: <elecraft@mailman.qth.net>
Sent: Monday, July 28, 2003 11:43 PM
Subject: [Elecraft] K2 MixW filter alignment question


I've always been a little confused by the whole filter alignment issue.
I have the new DSP option for my K2 but the original crystal filters,are the
ones I have the question about. I aligned them as instructed by the manual
and they seem fine...except for FL4 (200 hz) which seemed pretty attenuated.
Didn't worry much about it because the manual alludes to some attenuation. I
followed the instructions as well for using Spectrogram.
      Now here's my problem: I just used my MixW program (which I used to
use for PSK 31 on my Omni V) to look at the filters on the waterfall display
and with a signal on the band synced with my sidetone at  600 hz, its right
on the fuzzy edge of the 200 hz passband. If I tune it into the middle of
the passband (about 700 hz) its clearly louder. What have I done wrong and
and how do I fix it? I know this is a mucho stupid question. The signal is
not dead in the middle of the passband on any of the filter settings. Should
it be?
                           Andy W1AWB  K2 #3457


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