[Elecraft] IF xtal replacement mod

[Ron D'Eau Claire]

Several months ago when I replaced my filter crystals I saw a message
that caught my eye. I believe that it was from Eric or Wayne, pointing
out that with good i-f filter crystals the attenuation increases sharply
down near 200 Hz. That was why they recommended 400 Hz as the "narrow"
CW filter bandwidth. I haven't saved the message so I must work from
memory. It raised some questions because, apparently, somewhere in the
Elecraft documentation an example of 100 Hz for the narrow filter is
mentioned.

I noticed the message because I had used my FL4 at 200 Hz until I
replaced the crystals, but found that I did not like the sound of the
filter at that bandwidth with the new crystals installed. It wasn't so
much the attenuation, although I did notice that, but more the "sound"
of the filter. QRN and signals near the edge of the bandpass had a
"harsh" quality that I attributed to the distortion produced by the
steeper slopes at the edges of the passband. In my experience, there
really IS a place in this world for filters whose sides are not
vertical. 

It didn't matter to me since I normally operate CW with a bandwidth of 1
or 1.6 kHz or greater and do the filtering in my head. I just set my
"narrow" filter to 400 Hz. 

Ron AC7AC
K2 # 1289


"David A. Belsley" wrote:
> 
> Well, I replaced the 7 IF xtals and redid CAL FIL with spectrum 
> analyzer. I guess the results are good, although I didn't do any 
> before and after measurements.  The only negative is that my FL4 
> position, at 100Hz, is now much more attenuated relative to the other 
> BPs, roughly one S unit.  It was somewhat less than the others before 
> the mod, but not that much.  Any thoughts out there?