Hello, I have been operating this 40m QCX radio for a week or so now, making some nice contacts (mostly 300 to 500 miles during the daytime) and have a few questions about its operation:
1. Is there a noise reduction function on this radio? My ears have become spoiled by NR on my other radios, and I guess I view it now as close to a necessity. Is there a NR feature? If not, is there at least an attenuation function? Preferably an attenuation that can be easily adjusted on the fly, like, during a QSO, without digging deeply into menus?
2. Filtering. I read somewhere in the manual that the filter is set at 250 hz, but is there a way to dial it in narrower (see above comment about my having become spoiled by modern radios)?
TU and 73,
Brady KD8ZM

I believe if you watch Hans video it explanes the filter settings in the later part of the vid. Carl
https://www.youtube.com/watch?v=_Y89tMETDsQ

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

John,?
Thanks. That's probably more involved than I'd like to get, but I ordered one of the $15 CW filter kits from QRP Guys and am going to try it off board. If it doesn't work, I'm not out much! However, I am also bookmarking your note above in case the kit doesn't do the job. So, thank you for the guidance! ?

Have you watched the video? Hans does not appear in this video, nor is there anything about how to adjust the filter. ??????

开云体育

It shows how to adjust the cw offset, so i was wondering if that also changes the filter(s) peak frequency.

Steve,

Changing QCX CW OFFSET has no effect on the filter center frequency or bandwidth.


Brady,

Assuming you bypassed the onboard filter (discussed above) there is no reason QRP Guys filter will not work unless their input impedance is so much lower than QCX PHONES jack is designed to drive.

72, 73
John
N3AAZ

John - what would happen if I didn't bypass the onboard filter but instead went totally lazy and just plugged the filter kit into the earphone jack?

Brandon

Sure try the external audio filter, an experiment trumps analysis here. Every receiver tends to sound different. The qcx may grow on you. Being direct conversion it offers less distortion than most receivers. Do listen to discern if it has a flaw. Even try listening to another qcx on youtube. Hang in there while you sort this out, its a nifty receiver.

Curt

Brady,

If not bypassed (see my how to above), the onboard filter will have commanding influence and MUST be bypassed for the outboard filter to have command of the audio response.

Remember to, the test results of the QCX alignment procedure are based on the onboard audio filter, l suggest rerun the procedure before, then again after to see and hear the difference.

The serious CW OP will love the difference.

The known C22 mod from 10u to 0.1u will solve the thump problem.

72, 73
John
N3AAZ