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When using the SWR measurements in hardware tests I find the SWR reading is very unstable...varying from 1.5:1 to 2:1 in one particular case, this is true even when using a 50 ohm dummy load which shows a flat 1:1 SWR over the HF range on my nanoVNA.

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I wonder if anyone else finds this??

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73 Steve G4EDG?

Hi Steve,

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Make sure that you're not in practice mode.

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When I tried testing my SWR a little way back, I got similer results and wondered if I broke something. I then realised that I had the rig in practice mode. Once I disabled it, it was all fine again.

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Note that it doesn't transmit in digimode either when in practice mode.

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I hope that fixes it.

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Mel. M0KMD

I'm having the same effect (i.e. wildly fluctuating SWR readings when using an ATU + wire antenna) with at least one QMX out of my "collection" and always wondered what the reason was. After a retune and/or leaving the HW tests function and going into normal transmit the SWR usually is where it should be according to the bar indicator. Definitely not caused by practice mode.
Haven't bothered to do a systematic analysis though, i.e. will the effect go away when plugging in a dummy load, different ATU, bands affected, stray RF, one or all of my QMXs affected, etc. etc.
Something clearly is amiss though seems to be an issue with very few of us, judging from the low number of responses.
A dummy load should of course always produce a rock stable SWR reading.

On Tue, Mar 11, 2025 at 03:06 AM, RS wrote:

A dummy load should of course always produce a rock stable SWR reading.

Perhaps so in an ideal world.

In QMX+, on 6m and somewhat less on 10m, and perhaps also on some lower bands, the detected voltages from the SWR bridge (T507 and related components) don't get to the processor in a completely clean state.? There is a small level of RF induced into the PC board traces.? So when the processor reads those voltages and calculates the SWR, the voltages will have some amount of modulation, which appears as a fluctuating SWR reading.? ?Most often the fluctuation is only a few hundredths of an SWR unit, appearing in the least significant digit, but if that reading is close to a 1/10 boundary, the next digit up may also fluctuate.