On Fri, 14 Oct 2005 19:38:37 -0400, Ken Scharf
wrote:


That would work fine, but with the DDS, I can program the actual
frequency range to be swept and probably be able to calibrate the
scope face to read the actual frequency 'break' points on the filter.
Using the vxo method will get you a working filter quickly no
doubt, but I will still need the DDS vfo for the finished rig, so
I just figured I'd do that first.

Makes sense. I found the other way easy when DDS chips were 55$ each!
The varicap sweep is calabrated to the scope so that was not an issue
for sweeping the filter. I found that using wideband noise and a
sound card was better.

How many 'rocks' did you use in an SSB filter? I've seen some designs
on the web with 6 crystals, would the shape factor be any better with
8 or more? (with over 400 crystals in the junk box I can go crazy,
but I'd still have to find the capacitors :-).

I'd say 4 is a useable minimum. With that I'll add the skirts at 40db
down are not very good though. I've used 6-8 to get a good 6-60db
shape (under 2:1). There is a problem if you go for too many. The
filter can have enough group delay that while it's shape is good, the
sound has a hollowness.

The caps, once you figured the qalues you will likely end up using
parallel values. IE: 232pf may be a 220+12pf or a 220 and a 4-20pf
trimmer.

Allison