[Elecraft] KX1 IF filter tuning?

[Jeff Stai WK6I]

OK, here goes... has anyone put their KX1 on to Spectrogram to look at the filter shape? I have...

I have just completed KX1 #91 (finally!) and I have been doing some tuning 
around just to get used to it and practice with the filters etc.

It was bugging me that I could not seem to tune in stations at narrower 
filter settings at the pitch I was expecting - they were always a lot lower 
than the sidetone pitch of 600Hz. In fact, at times it seemed as if there 
were two peaks - which I dismissed as QSB of course...

Well, I decided to haul out my vintage N0SS noise source and spectrogram 6 
to take a look at things - and sure enough, it does not -seem- right - in 
summary:

1. at the narrowest Filter setting (full CCW) the filter is centered at 
465Hz, with a nice shape (BW not measured)

2. as the Filter control is moved CW, two peaks start to appear.

3. the lower peak is always below 600Hz, while the higher peak moves higher 
with wider settings (more CW)

4. the trough in between the peaks is -8dB to -14dB (relative to the lower 
peak) after the 12 o'clock position (when I started measuring it)

5. at wider settings the higher peak was weaker than the lower peak


Here is the raw data:

(CCW) * 465Hz single peak

  0.5 * equal peaks at 415Hz and 540Hz

      * equal peaks at 425Hz and 630Hz

  1.0 * equal peaks at 440Hz and 810Hz, trough at 620Hz -8dB

      * peak at 470Hz, peak at 1055Hz -5dB, trough at 780Hz -10dB

  2.0 * peak at 515Hz, peak at 1310Hz -9dB, trough at 1000Hz -12dB

(CW)  * peak at 540Hz, peak at 1425Hz -12dB, trough at 1075Hz -14dB


Other possibly meaningful things to know:

1. All options are installed, though I was noticing the issue before I 
installed the ATU and 30m option.

2. I have performed the BFO and DDS adjustments described on pg 68 - the BFO 
did require a -19 adjustment, which did what it was supposed to do to WWV 
(again noting that I was having the tuning problem before I did this, and 
thought it might help.)

So, um, any ideas...? thanks! - jeff wk6i


--
Jeff Stai               jds@twistedoak.com
Twisted Oak Winery      http://www.twistedoak.com/
Rocketry Org. of CA     http://www.rocstock.org/
Amateur Radio           WK6I