[Elecraft] Filter Crystals

Mon Dec 16 20:07:32 2002

When I first built SN#1289, I set up CW filter 4 for 100 Hz and it
worked just fine! 

Then I discovered that I could NOT set up my BFO for decent sound on
OPT1 for SSB. It turned out that I had a poorly matched set of crystals
and replaced them. I had to replace all of the crystals in order for the
SSB and CW filters to "line up" properly. Up until then I had no gripe
at all about the CW filters.

Replacing the crystals fixed up my SSB filter just fine. Then I noticed
that if I tried to use 100 Hz bandwidth for filter 4 on CW, I had a
"rough" sounding filter and lots of attenuation. 

Checking into it, I found that Elecraft does NOT recommend using a
bandwidth as narrow as 100 Hz because of the excessive insertion loss in
the filter. I decided that the "roughness" probably came from artifacts
created by sharper "skirts" on the bandpass. (Contrary to much popular
belief, filters with vertical "sides" or "skirts" at the edge of the
bandpass are not always desirable). Opening up the bandpass to 400 Hz
produced a much more pleasant filter characteristic for me and got rid
to the noticeable insertion loss.

Ron AC7AC
K2 # 1289. 

I have K2 # 2571.  I am one of those people who want my rig to work as
well as possible.  I am having trouble with the decision whether or not
to replace my filter crystals.  The filters are set up for a pass band
of 1.5khz, 700hz, 400hz and 100hz.  Here is the symptom I would be
trying to eliminate. I loose 10-12db of signal strength when I switch to
the narrow 100hz filter.  Is this normal?  I set my filters using
Spectrogram and the signal loss was measured with this software.  Any
help would be appreciated.

Thanks
Brent   

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