Arne,
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Look at the schematic around T507 on the last page.
If the QMX shows a roughly correct power out reading when driving a 50 ohm dummy load,
that means that ADC_FWD has a proper voltage on it for the STM32F processor to detect.
In this case ADC_REV should be close to 0 Volts.
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When expecting an "absurd SWR", the voltage on ADC_REV should rise to approach where ADC_FWD is.
(Reduce supply voltage to avoid blowing the BS170's when you expect a high SWR.)
Verify that ADC_REV remains near 0 Volts with a voltmeter,
then?check for opens, shorts, and failed parts around D515 and R524.
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Jerry, KE7ER
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On Wed, May 21, 2025 at 09:05 AM, SA6ZGM Arne wrote:
Thanks,
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I've now tried the dummy load from QRP Labs, and a couple of antennas that should produce absurd SWR at some settings. All the while, the QMX+ shows SWR between 1.00 and about 1.10-1.20.
