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I have a question for all you extremely BRIGHT people out there.
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Watching how the sBitx works, and thinking through how it mathematically computes the single side band modulation, based on a transform of the analog audio input, I am thinking that it is impossible to "splatter" outside the normal bandwidth.? ?That would be highly desirable, because it basically means you don't need ALC (automatic level control) and that you sorta have a "built in compression" if your audio gets louder.
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Am I right in these thoughts?? ? I've studied the ALC circuitry by putting some debugging print statements in it, and I don't think I've ever seen it do much at all and this was part of what got me thinking that this radio may simply NOT produce splatter.
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Your input welcomed,
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73
Gordon Kx4Z
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There is some kind of control on the alsa mixer, because earlier, when the topic of discussion was why the output signal is smaller during digital transmission, I saw this. Call the alsa mixer and try to adjust the volume, the slider automatically jumps back to a level when transmitting. I didn't look any further for where this is set, but the regulation works.
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Gyula HA3HZ |
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Gordon,
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I believe that this radio can produce "splatter" if the level is set too high.? I have not looked into the code, so I do not know if any key shaping is done in CW mode, for example.? Overdriving the audio can also produce splatter.? The PA gain (NOT Mic gain) is post DSP filters, so splatter is still possible.?
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Splatter is one reason the QRP-Labs QDX is not suitable for CW operation.? The QDX lacks key shaping, even though it is a single-frequency signal generated directly from the Si5351.
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I could be wrong so that I will look for others' comments.
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73
Evan
AC9TU |
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Thanks, Evan!? ?I agree that if you overdrive the finals you can produce IMD.? ?But I think the modulation is by Fourier Transform and band-limited in the Fourier Transform, so unless the transform errs, how can it produce a time-domain output that has signal strength outside of the limited set bandpass of the creation?? ? ? That intrigues me.? ? ? Also, I watch a number of my friend's signals on the spectral display and I see a lot of wasted energy in their lower-frequency parts of their audio signal.? ? When it is the higher frequency parts that are so important for speech recognition -- especially with older ears with possibly lower response?in the mid and higher range.? ? Before this radio I didn't really ever see that stuff.? ?? Interesting. Gordon KX4Z On Mon, May 12, 2025 at 7:00?AM Evan Hand via <elhandjr=[email protected]> wrote:
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Isn't splatter in CW mode caused by the rapid rise of the signal on key down or rapid fall on key up?? How is that handled in the sBitx?? Is there a level control that uses a raised cosign or similar algorithm to prevent key clicks?
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I must look into the code to see how CW is being processed.
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73
Evan
AC9TU |
HA3HZ