I have built my QMX+ for 9 volts. When I run the TX test from the putty window, it shows the TX voltage as 7.5 volts. This is presumably the voltage at the source of the modulator FET as measured by the ADC_PA port on the schematic. With my QDX, a 9 volt build puts close to 9 volts at that point in the circuit. The question is, can I run my QMX+ supply voltage higher than 9 volts for FT8/CW operation? What about SSB?

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Tony

AD0VC

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Interesting question, Tony.? I happened to have my open QMX+ on the bench along with a DMM and oscilloscope, so I measured the voltages.? My build is for 12V.

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The diagnostic screen shows supply voltage at 11.8V.

My DMM measures 11.84V at the source of Q507 (about the same as supply voltage, as expected).?

When I do 'T' to transmit in the diagnostic screen, the supply voltage displayed goes down to 11.5V, and the measurement at the source of Q507 is 11.48V (very close, as expected)

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Measuring at the drain of Q507, which is the TX voltage measured by 'ADC_PA' and displayed by QMX+:

? diagnostic rx mode: 0.4V displayed, 0.43 measured

? diagnostic tx mode: 9.8 displayed, 11.22V measured (just 0.26V drop from V+)

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So the Tx voltage displayed by my QMX+ is a full 1.4V lower than what is measured by a DMM.?

A measurement with my oscilloscope verifies the measurement, and shows a clean DC signal.

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Apparently, the QMX Tx voltage measurement via (ADC_PA) is not well calibrated, and gets off by 1.4V on the high end.

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So in answer to your question, can you run your QMX+ on a higher supply voltage, the answer is: NO.

The real TX voltage is close to the supply voltage.

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Why?? Seems like a question for Hans, I'll post separately.

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Stan KC7XE

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