Thursday, June 2, 2016

CWAZ filter

Playing with the little buffer amp, I noticed the output was pretty messy - the 2nd harmonic was really high.  (Oddly, when I first built this without the output cap, it didn't look that bad.  But it was also putting out 6v p-p and probably would have burned out in a minute...)

I figured at some point I'd need to build a low pass filter, so this seemed like a good time.  Looking around, the CWAZ lpf design seemed popular, and I found this pdf from GQRP on how to build one.

I realized I was running low on called-for T37-6 toroids, as I used some in the DC receiver.  But then I remembered I cut one out to replace the VFO with the AD9850.  And it was already wound just like I needed!  How often does that happen?  The other two were fast to wind, and I picked out the capacitors from my junk box.

I hooked it up to the amplifier and looked at the output

Without filter

With filter
So, it looks a lot better.  Need to do some more experiments, but maybe ok?

P.S. I finally found out that "CWAZ" here stands for "chebyshev with added zero"