[Elecraft] K2 Filter Shape Factors

[Don Wilhelm]

Bill,

It is difficult to set the filters properly using a single signal input to
the K2 - it is much easier if you use wideband noise.  Use either 'dead
band' noise or better yet a noise generator such as the Elecraft N-Gen.  Use
Spectrogram or similar to observe the audio spectrum on the computer screen.

Check out my website www.qsl.net/w3fpr article on Dial Calibration for a LOT
more information on CAL FIL.

Looking at your BFO settings, it seems you have the BFO on the same side of
zero for both CW and CWr.  I just checked my settings to give you an idea -
they are as follows:
Filter BW   CW   CWr
1.20           124    166
0.75           117     163
0.50           115     161
0.10           111     160

The above values produce a sidetone of 600 Hz - with your 400 Hz selection,
your CW numbers will be a bit higher and the CWr values will be a bit lower
(frequencies closer to the filter center).

By looking at the passband using Spectrogram and the wideband noise
generator, you will be able to actually see the shape of the passband.  I
can tell you that the passband does develop significant ripple at wider
bandwidths.  That is one reason my widest CW bandwidth is set at 1200 Hz.

73,
Don W3FPR

----- Original Message ----- 

> I just went through filter realignment using my
> preferred Pitch setting of 400 Hz.  I did this simply by
> using the XG1 as a signal source and adjusting all CW
> filters for equal passband difference on both sides of zero
> beat.  I used the K2's meter and tuned for one display
> bar down (S7 with no flicker) on both sides of the XG1's
> calibrated S9 output.  I have no idea how many dB down
> S7 is but that's not critical to centering the passband of
> the filters.
>
> It seems to me that the filters have some unusual
> shape factors, and I wonder if anyone has noticed the
> same?  For example, here are the 2 S-unit bandwidths
> I measured after adjusting my BFO settings:
>
> Filter S9-S7 BW*
>
> 1.50 190
> 1.50R 190
> 0.70 340
> 0.70R 350
> 0.40 210
> 0.40R 200
> 0.10 190
> 0.10R 180
>
> (where "R" means CW Reverse.  )
>
> *For the 100 Hz filter, I used the S7-S5 transition since
> the XG1's S9 output is attenuated to S7 by that filter's
> higher insertion loss.
>