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When saying that the QMX has a new method of SSB modulation,
we should acknowledge the history behind it.
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Leonard R Kahn first proposed something like this in 1952, what he called Envelope Elimination and Restoration, or EER.
His paper is found in the Proceedings of the IRE, Volume 40, Issue 7, July 1952.
The output of a standard SSB exciter (either filter or phasing method) was sent down two paths.
One path clipped it down to a radio frequency square wave of uniform amplitude, eliminating any envelope information.
The second path had a standard AM demodulator, creating an audio rate signal that held the envelope information.
The square wave then drove an efficient class C amplifier, the power supply to the class C amplifier was modulated
using the audio rate envelope information.??
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This method worked, it was used mostly in very high power commercial SSB transmitters.
A few transmitters were built for amateur use but were not very successful, as the extra efficiency
was hard won due to the extra complexity.
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In 2019, Guido (PE1NNZ) created code for the Atmega328 that computed the frequency and envelope
information mathematically, and used this to allow a slightly modified QCX to transmit SSB signals.
The resulting signal is not particularly good given the limitations of the 8 bit processor, but it showed the way forward.
/g/QRPLabs/topic/29572792
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Hans has now created the QMX, it has a modulator at Q507 and enough processing power in the STM32F446
to generate a clean SSB signal.? He has also made significant enhancements to the software algorithm.
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The approach Guido and Hans have taken is significantly different than anything before.
The frequency and amplitude information are generated mathematically, not stripped from a traditional SSB exciter.
Somebody will have to come up with a catchy name for this since it is no longer Envelope Elimination and Restoration.
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Jerry, KE7ER
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On Mon, Jan 27, 2025 at 05:46 AM, Jerry Gaffke wrote:
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