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QCX CW Filter

 

I built a QCX for 20 meters the other day. It went well. I powered it up, aligned it, and immediately made a QSO. It put out 5 watts at 13.8 volts without any adjustment.

I¡¯ve noticed that the CW filter isn¡¯t very tight though. I can hear strong stations from 100 Hz to 1800 Hz as I tune up and down the band, although largely diminished when off of the 700 Hz center frequency, but not quite gone. I¡¯ve looked at that portion of the board and can¡¯t find anything obvious. Any ideas?

Mac, KB9HV
 

Check the voltages on ICs 8 and 9. Look for wrong capacitors or resistors in that area as well (assuming you are talking about a QCX Classic or QCX+). If it's a mini, then all that is pre-soldered SMD and probably correct but you can still check the voltages around the two ICs, and look for any SMD parts that may have been dislodged during construction. Typically, you should?see fairly strong stations drop off almost completely with only one or two 100 Hz tuning steps either way of center.

Ron

On Sun, Dec 31, 2023 at 1:24?PM Mike McCarty <mmccarty@...> wrote:
I built a QCX for 20 meters the other day. It went well.? I powered it up, aligned it, and immediately made a QSO.? It put out 5 watts at 13.8 volts without any adjustment.?

I¡¯ve noticed that the CW filter isn¡¯t very tight though.? I can hear strong stations from 100 Hz to 1800 Hz as I tune up and down the band, although largely diminished when off of the 700 Hz center frequency, but not quite gone.? I¡¯ve looked at that portion of the board and can¡¯t find anything obvious.? Any ideas?

Mac, KB9HV
 

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Sorry, it is a QCX mini. ?

-KB9HV

On Dec 31, 2023, at 2:34 PM, Ronald Taylor <wa7gil@...> wrote:

?
Check the voltages on ICs 8 and 9. Look for wrong capacitors or resistors in that area as well (assuming you are talking about a QCX Classic or QCX+). If it's a mini, then all that is pre-soldered SMD and probably correct but you can still check the voltages around the two ICs, and look for any SMD parts that may have been dislodged during construction. Typically, you should?see fairly strong stations drop off almost completely with only one or two 100 Hz tuning steps either way of center.

Ron

On Sun, Dec 31, 2023 at 1:24?PM Mike McCarty <mmccarty@...> wrote:
I built a QCX for 20 meters the other day. It went well.? I powered it up, aligned it, and immediately made a QSO.? It put out 5 watts at 13.8 volts without any adjustment.?

I¡¯ve noticed that the CW filter isn¡¯t very tight though.? I can hear strong stations from 100 Hz to 1800 Hz as I tune up and down the band, although largely diminished when off of the 700 Hz center frequency, but not quite gone.? I¡¯ve looked at that portion of the board and can¡¯t find anything obvious.? Any ideas?

Mac, KB9HV
 

Hi Mac
Are you sure there's something wrong with it? In my experience the CW filter on a QCX is very soft compared to my K2 and KX3.? The QMX sounds steeper but still soft compared to a crystal roofing filter and dsp.? What are you comparing it to, are you used to a really tight, steep filter?

HNY and 73

Peter, GM0EUL
 

Agree with GM0EUL, it is an analog filter with skirts (IIRC) of ?-12 dB/octave, so a signal 350 Hz higher or lower would be only 12db quieter, and therefore adjacent strong signals will still be very audible.?
 

On Mon, Jan 1, 2024 at 12:10 AM, Peter GM0EUL wrote:
Are you sure there's something wrong with it? In my experience the CW filter on a QCX is very soft compared to my K2 and KX3.
Agree. The first time I used a radio without really sharp filtering it was quite a shock just how much activity I could hear above and below the frequency I was tuned on.?

The QMX is pretty good. I was using my Kanga Rooster yesterday though and there was a cacophony of dits and dahs either side of me.?

These days I don't think anything of it but it is distracting at first, particularly to a newcomer to CW :)

Danny M0SDB?
 

Hi Danny, Peter, all

Attached is a comparison of the QCX vs QMX CW filtering. These are actual measured responses. Not simulation or calculation. It's quite clear how much steeper the QMX filter edges are. Which is normal because QMX uses DSP filtering.

73 Hans G0UPL


On Mon, Jan 1, 2024, 3:37?PM Danny Bower <m0sdb@...> wrote:
On Mon, Jan 1, 2024 at 12:10 AM, Peter GM0EUL wrote:
Are you sure there's something wrong with it? In my experience the CW filter on a QCX is very soft compared to my K2 and KX3.
Agree. The first time I used a radio without really sharp filtering it was quite a shock just how much activity I could hear above and below the frequency I was tuned on.?

The QMX is pretty good. I was using my Kanga Rooster yesterday though and there was a cacophony of dits and dahs either side of me.?

These days I don't think anything of it but it is distracting at first, particularly to a newcomer to CW :)

Danny M0SDB?

 

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Thank you to everybody. ?I figured the response might be ¡°That sounds about right¡±. ?I just wanted to double check. ?I have a QMX that my son finished building yesterday and I was comparing them side by side this morning. ?It was apparent there was a difference between the two, but I knew the filtering was all DSP on the QMX.

Tnx agn and have a happy new year.

KB9HV

On Jan 1, 2024, at 7:20 AM, Hans Summers <hans.summers@...> wrote:

?
Hi Danny, Peter, all

Attached is a comparison of the QCX vs QMX CW filtering. These are actual measured responses. Not simulation or calculation. It's quite clear how much steeper the QMX filter edges are. Which is normal because QMX uses DSP filtering.

73 Hans G0UPL


On Mon, Jan 1, 2024, 3:37?PM Danny Bower <m0sdb@...> wrote:
On Mon, Jan 1, 2024 at 12:10 AM, Peter GM0EUL wrote:
Are you sure there's something wrong with it? In my experience the CW filter on a QCX is very soft compared to my K2 and KX3.
Agree. The first time I used a radio without really sharp filtering it was quite a shock just how much activity I could hear above and below the frequency I was tuned on.?

The QMX is pretty good. I was using my Kanga Rooster yesterday though and there was a cacophony of dits and dahs either side of me.?

These days I don't think anything of it but it is distracting at first, particularly to a newcomer to CW :)

Danny M0SDB?

<cw comparison thick.png>
 

On Mon, Jan 1, 2024 at 05:20 AM, Hans Summers wrote:
Which is normal because QMX uses DSP filtering.
?
...is it possible to set the center frequency for either of the QxXes?

Happy New Year to all of you!
73 de Razvan dl2arl
 

Hello Razvan

On QCX if you wish to change the center frequency you must do so with hardware component changes since it is analog. You can also change in the configuration menu, the CW offset to match the new center frequency.?

On QMX the filter is not currently adjustable either (though it will be in future firmware updates); currently you are able to change the sidetone frequency and the CW offset frequency in the menu. You can choose a CW offset frequency between 600-900Hz. This will still be inside the 300Hz bandwidth?CW filter of QMX currently.?

73 Hans G0UPL



On Mon, Jan 1, 2024 at 9:41?PM DL2ARL <dl2arl@...> wrote:
On Mon, Jan 1, 2024 at 05:20 AM, Hans Summers wrote:
Which is normal because QMX uses DSP filtering.
?
...is it possible to set the center frequency for either of the QxXes?

Happy New Year to all of you!
73 de Razvan dl2arl

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