Brady,
Audio filtering in the QCX is fixed and way too sharp for my CW and WSPR pleasure.
I built several outboard audio filters with great success.
Take? a lQQk at this site
?http://www.bowdenshobbycircuits.info/opamp.htm
Drop down to? "2nd Order Opamp Filters" where there is 200 Hz math? example then plug in your pleasure.
I also have first hand experience here...
>>>>http://www.circuitstoday.com/band-pass-filters<<<<
I plugged these? math equations into EXCEL
then built several BPF and variable band pass
THAT WORKED FIRST TIME.
With an outboard audio filter...
You will need to bypass the QCX onboard audio filter:
Locate R27 and R29.
Lift (unsolder) the leg of R29 that connects to R27.
Lift (unsolder) the plus (+) leg of C21.
I found it much easier to cut the trace between C21 (+) and IC9A (pin 1).
Solder a jumper from the now open pad at R29 to C21 (+) pad, then
plug your outboard filter into the PHONES jack.
Note sidetone and volume work just as before.
If you re-run the alignment procedure ...
you must realize the test results were/are based on the onboard filter installed.
I suggest re-run the procedure with the outboard filter just to feel and hear the difference,
I like it and think you will too!
If known mod of C22 not installed yet, replace C22 (10uF) with (0.1uF).
72, 73
John
N3AAZ
