On Aug 25, 2023, at 10:38 AM, John Z <jdzbrozek@...> wrote:

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Dan,

The QMX has a PMOSFET modulator that can gracefully ramp down the supply voltage to the power amplifier stage, under digital/MCU control. That circuitry is essential for the QMX wave shaping function and to it's future SSB functionality. It doesn't exist on QDX, and so a firmware solution for QDX is not possible.

Is the inductive spike damaging transistors on QDX??

Hans and I have had a lively debate on that subject, with he of the opinion that the energy level is too low to do damage, and I of the opinion that it is responsible for some, perhaps many of the fails attributed to high SWR.

A big problem in resolving the question is forensics: How do you know which mechanism is responsible? A dead part looks the same either way, and usually winds up in the trash!

JZ KJ4A?

On Fri, Aug 25, 2023, 10:12 AM Daniel Walter via <nm3a=[email protected]> wrote:

John,
Your explanation of QDX L14 makes sense. It doesn't seem to be a serious problem for semiconductor failures tho. More of an issue for spectrum 'dirtiness'. The diode would take care of both concerns.?

I wonder why it could not be taken care of in the QDX firmware, as it has been with the QMX. There doesn't seem to be the memory and processing constraints of the QCX, even though it doesn't have the capacity of the QMX processor. ?
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73, Dan? NM3A

And, of course, the third question is if adding the commutating diode and/or the zemers will affect the output characteristics (spectral purity, spurs, harmonics), in such a way as to render transceiver illegal to operate.

73, Willie N1JBJ

On Aug 25, 2023, at 10:38 AM, John Z <jdzbrozek@...> wrote:

?
Dan,

The QMX has a PMOSFET modulator that can gracefully ramp down the supply voltage to the power amplifier stage, under digital/MCU control. That circuitry is essential for the QMX wave shaping function and to it's future SSB functionality. It doesn't exist on QDX, and so a firmware solution for QDX is not possible.

Is the inductive spike damaging transistors on QDX?

Hans and I have had a lively debate on that subject, with he of the opinion that the energy level is too low to do damage, and I of the opinion that it is responsible for some, perhaps many of the fails attributed to high SWR.

A big problem in resolving the question is forensics: How do you know which mechanism is responsible? A dead part looks the same either way, and usually winds up in the trash!

JZ KJ4A





On Fri, Aug 25, 2023, 10:12 AM Daniel Walter via groups.io <nm3a@...> wrote:

John,
Your explanation of QDX L14 makes sense. It doesn't seem to be a serious problem for semiconductor failures tho. More of an issue for spectrum 'dirtiness'. The diode would take care of both concerns.


I wonder why it could not be taken care of in the QDX firmware, as it has been with the QMX. There doesn't seem to be the memory and processing constraints of the QCX, even though it doesn't have the capacity of the QMX processor.
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73, Dan NM3A

Hi Willie

And, of course, the third question is if adding the commutating diode and/or the zemers will affect the output characteristics (spectral purity, spurs, harmonics), in such a way as to render transceiver illegal to operate.

Yes, spot on. That, and whether the diode and/or zeners add anything to the receive noise floor. Probably not. But I need to measure, simulation isn't good enough for me :-D

I tried to order some 47V zeners but got BZY47. Which is 9.1V. Sent back, and got BZY47 **again**. I should put in a large Digikey order in the next couple of weeks and will add some to it. Here Digikey orders take 10 days and incur a significant expense so you can't do it for a sub $1 order like you can in US.

73 Hans G0UPL

Chris, is this with or w/o Zeners?
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73, Dan? NM3A