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Yes, there should not be any problem doing that. As I noted in the manual, the CW filter in the QCX is a slightly modified version of the Hi Per Mite filter, with kind permission from Dave NM0S. The modifications are related to DC bias and NOT having the LM386 audio amplifier. So the spreadsheet on the 4SQRP website for calculating resistor values DOES apply equally also to the QCX.?

Some observations:

1. According to my measured unwanted sideband suppression chart the unwanted sideband is still -40dB down even at 450Hz, some way away from the 700Hz centre. But, I had optimised my phase shift adjustment for the 700Hz centre. You should have no trouble adjusting the phase shift to optimise it at the lower frequency.?

2. You will need to change the "3.8 CW offset" parameter from the default 700Hz, to your 450Hz. Similarly change "8.2 I-Q bal frq" from 700Hz to 450Hz. You can also change menus 8.3 and 8.4 to suit your lower audio centre frequency.?

3. The Digital Signal Processing (DSP) filter is fixed on a centre frequency of about 750Hz with 250Hz bandwidth. This filter applies additional filtering on top of the analogue CW filter but its output is used ONLY for the CW decoder, and during the alignment on-screen measurements. If your analogue centre frequency is 450Hz and the DSP is on 750Hz, then the performance of the CW decoder will be considerably reduced. So bear this in mind, if using the CW decoder is very important to you. Note that this caution only applies to the use of the CW decoder for decoding received signals. The CW decoder will still work fine for your own transmissions, in the CW keying practice mode, and when using the decoder to enter configuration parameters such as stored messages. In these cases the CW decoder is driven directly by the key, without the DSP.?

What I will do in the next firmware version is add a configuration parameter that lets you choose the DSP centre frequency from 250, 500, 750, 1000Hz. That way if anyone wants to move the analogue filter centre frequency away from 700Hz then they can also move the DSP centre frequency to the nearest suitable selection. In your case it would be 500Hz.?

73 Hans G0UPL