Adam,
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The SSB modulation scheme that Hans is using generates true SSB.
This SSB signal will potentially be cleaner than that from a typical transmitter?
using the traditional filter or phasing methods followed by a linear amplifier.
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For a narrow band of RF frequencies roughly 3000 Hz wide, the sum of
all the component frequencies of the Fourier transform added together
is a single sine wave that varies in amplitude and a little bit in frequency (or phase).
Those variations both happen at audio rates.
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A simple example of this is a standard SSB two tone test signal, for which
an exact solution can be found: ?sin(a)+sin(b) = 2*sin((a+b)/2) * cos((a-b)/2)
So the result of two sine waves at 7000 and 7002 KHz summed together is
a sine wave of 7001 KHz multiplied by (modulated by) a cosine wave of 1 KHz,
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The QMX can vary the frequency by steering around the Si5351 oscillator
via the I2C bus, and can adjust the amplitude using the modulator at Q507.
The result is a totally new method of SSB modulation, made practical by the
computing power of modern processors such as the STM32F446.
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See this discussion:
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Jerry, KE7ER
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On Mon, Jan 27, 2025 at 03:54 AM, Adam wrote:
There are some voices on the group saying that digital modes requiring
multiple frequencies will work once the SSB is done.
My assumption is that the QMX doesn't have a proper SSB modulator, it just
has a single frequency synthesiser ('5351) and a way to modulate amplitude
of this single-frequency signal, and apparently some clever things can be
done with this limited hardware to make the resulting signal sound like
SSB.
But will it be "true" SSB? Will it work for MFSK digital modes, or is it
just some sort of an (impressive) hack to make voice recognizable?
