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Dan, The QMX modulator can gradually increase or decrease transmit power in response to its DAC input. One possible use might be to recognize a "tune" mode and preemptively reduce power to a safe value. Response to high SWR is another use. Yes, timing might be critical, but in the case where high SWR is the result of a low load impedance, the transistor failure mode is over-current and over-heating. ?You have a little time then to respond in that case. The highly reactive load over-voltage case could be a different matter. The modulator can also be used for wave shaping a CW dot or dash, or it can be used to impress audio modulation onto a carrier. It can be used to reduce the di/dt portion of the equation V = L di/dt at the end of a transmission, thereby killing off the dangerous inductive spike. Think of it as applying a little wave shaping at the end of an FT8 burst. On your SSB question; Yes SSB is very different from the digital modes.? FT8 for example transmits at a constant amplitude but with a varying tone frequency.? SSB will be generated in QMX by modulating the angle/frequency of the carrier signal, amplifying it in an efficient but nonlinear power stage, and then impressing an audio amplitude modulation signal onto the final amplifiers power source rather much like an old style AM transmitter. The resulting varying angle/magnitude vector simulates an SSB signal The rub here is that at the lower output levels at the finals, the amplitude you command with the DAC is not necessarily what you actually get.? As the drain voltage of the final amplifier decreases, the drain capacitance of the transistors increases sharply. Zeners would do the same thing. This results in knocking the output filtering around, changing the output power in ways which adds audio distortion to the transmitted signal. The generally accepted solution is to pre-distort the audio in a compensating way. It's tempting at that point to say " Easy! The audio is digitized. It's just a game of numbers!" Sure, but which numbers do you use? That depends on how much pre-distortion is required and the answers could be different with or without Zeners. Regards and 73,? JZ KJ4A? On Mon, Jul 17, 2023, 11:00 AM Daniel Walter via <nm3a=[email protected]> wrote:
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