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On Thu, Mar 27, 2025 at 05:19 PM, Ellis Simon GM4GZW wrote:

The phase calibration sweep for 20M also looks odd and is different to the others which are all nice curves

Based on some experimentation with some similar phase calibration results on a couple of bands on two of my QMX, it appears to me that when the phase distortion curve is started, but not completed, then the audio gets distorted.? And the lower the value it stops at, the worse the distortion.? In your example, the curve of values only goes to about a value of 600 on the horizontal DAC axis.? So my theory is that whenever your voice waveform has an amplitude that results in any DAC value of over 600, there is not a proper result stored in the calibration table for those values, and 'bad stuff happens', resulting in distorted audio.

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So (if my theory is correct, and it seems to have worked on my 2 QMX), if you can get the calibration to put in measured phase values across the whole range of the DAC (about 2600 for 12V builds and 2000 for 9V builds), then the resulting voice quality is good, even if the graph looks uneven or strange.

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I was able to get my calibration to finish on the 'bad' bands by adjusting (as others have noted) the "Frequency min" and/or "Frequency center" in the band configuration screen.? For some reason these do affect the way the phase calibration runs.? I had to play with different values in one or both of those settings, but without too much trouble got all of the bands to have "complete" phase distortion curves.? The 'curves' were not always pretty, but I don't think that's so much the issue as having data initialized for the full range of DAC values? that will be used (based on the input voltage and drive level, both of which Hans pointed out need to be set before calibrating).

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After I changed the band config settings for calibration, I restored the band settings to their original values so the other diagnostic sweeps would still function in the same way, and so my default 'center frequency' would be what I want on each band.? [These settings don't affect normal transmit/receive operation, we just needed to 'seed' them differently to get completion of the calibration table.]

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I hope this is helpful to someone, and maybe someone can corroborate my theory on getting rid of the distorted audio....

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Stan KC7XE