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While working on another problem I had a strange issue with bad QRM coming through the radio.? I tried a number of things, swapping around coax, adjusting location of things, but couldn't supress it.? Then I noticed that my SWR was oscillating between 1 & 2....; running an SWR sweep confirmed the strange behaviour.? A power off/on didn't sort it, and switching band didn't seem to make much difference.

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Eventually, on a whim, I did a factory reset..... and it was gone!? Has anyone seen this behavior?? A software gremlin?? Or a hardware issue with my build?

Later, I noticed that doing an audio filter sweep leaves the radio making a lot more noise, which a power-off will sort.

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I'm hoping these are just firmware/bugs!? In operation the radio seems to be operating perfectly....

Chris,

Thank you for this post.? My QMX had the "dancing" SWR issue. A Factory reset calmed it. Where the SWR was varying 1+, it is now varying? 0.01.

Thanks for the confirmation Steve.

This oscillating SWR problem is becoming annoying; my unit seems to slip into that mode at the drop of a hat, and then I have to factory reset and lose my settings.? I'm curious if anyone else has an theories for the cause; or how I might go about fixing it?

I wonder if Hans is aware of the problem and there might be a firmware improvement at some point, or if there is a tolerance issue with something I've done and my unit is just more prone to it?

Chris, this likely isn't "just" a firmware problem.? Otherwise, many of us would have the same issue and be trying to figure it out.

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More likely, it is a combination of something in the hardware of your particular radio and/or how you are using it that triggers the problem.? Certainly since it can be fixed (at least momentarily) with a Factory reset, it does somehow relate to firmware and/or configuration settings.

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Perhaps information like the following would help give a start in diagnosing the problem:

1) Which model of QMX do you have, and which board revision?? Any mods applied?

2) Which version of firmware are you running (I presume the latest, 027)

3) After you do a factory reset, exactly which changes do you make to the default settings?? Maybe there is something you are setting that pre-disposes this behavior, and knowing the settings perhaps would enable others to replicate your problem.

4) Which mode are you operating in when the problem occurs, and are you operating the QMX standalone, or tethered via USB to a computer?

5) Does this occur when operating on any band, or is it always on a particular band?

6) Does it start spontaneously at any time (i.e. just receiving), or is it always triggered when you transmit? Obviously you can only see SWR when you transmit, but you also said there was a large receive noise.? Does this receive noise always occur when this happens? i.e. does it seem like the condition persists even when not transmitting?

7) What kind of antenna are you operating into when the problem occurs (general type), and are you using a common-mode-choke on your feedline?

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It seems that there are not many places in the circuitry or firmware that could cause or contribute to such behavior.? An "oscillating SWR" could occur when there is some faulty behavior in the PA and/or the SWR bridge circuit, or perhaps the clock generator.? Perhaps the power and SWR truly are "oscillating" due to some internal condition (which you should be able to see on an external power/SWR meter), or perhaps there is just a problem with the SWR bridge itself, causing it to self-resonate, not affecting real output power.?

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Sorry, I just have questions and no answers...

Stan

Chris,?

I experience this behavior every time I trip the SWR protection circuitry.?
The only difference in my situation is that I can clear the issue with a power off/on cycle.?
It occurs on my LB and HB QMX radios. I read somewhere you could reset a SWR trip by just entering the menu. ?My radios will reset the trip, but the crazy SWR readings still exist.?
My LB is version 1, SN 105. Purchased the night Hans announced the QMX. The HB is version 4. SN ??? ?Purchased Dayton 2024. I use a common mode choke at the radio, RG58 several turns around a 240-43 core. The radio is 12 V. ( I doubt any of the last info matters here, but the age between the radios suggests the situation is not new ).?

73

Dick

W4PID?

Thanks Stan, I will try to reproduce how this occurs.? I'm on the 'latest' QMX, with no mods, with the latest firmware.
Typically, since I'm learning morse, I haven't transmitted anything but basic tests.? I tend to have an EFHW aerial with a common mode choke or a 50Ohm Load.? I'm often in Practice mode, the sidetone is turned up.? I listen on different bands, not all resonant on the EFHW. Perhaps that's a problem with the sensitive SWR.? Usually though, I'm on 40m.
It definitely happens without the USB connection.? I'm not sure beyond this what triggers it, but I will try some tests to figure it out.
I can never clear it with menus, power cycle, so far.? Only a factory reset.....? I will double confirm that though.
Your comment about the SWR bridge itself is interesting.? ? I have a NanoVNA, so I will try to compare SWR with what the aerial actually is.

I appreciate your feedback!

Thanks Dick, when you say 'trip the SWR', do you do anything in particular?? Unplug aerial, attach a non resonant EFHW, etc.?? It is sounding like this may well be my problem.

A couple of more notes:

a) Just 'receiving' with a poorly matched antenna or bad swr can't hurt anything in QMX.? Transmitting into a poor connection or bad swr can indeed cause problems.? Hopefully you have SWR protection enabled and set to 3.

b) Looking at your antenna with your nanovna will definitely be instructive.? Make sure it shows a stable SWR or return loss curve.? Sometimes a bad connection in the antenna feed will cause an intermittent failure that can show up on the nanovna as unstable traces, especially if the wind is blowing or you are moving the feedline.? But you won't likely see the oscillations, which are likely internal to QMX.

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Is your QMX a low-band, mid-band, or high-band version? or a QMX+?? And as you get time to get answers to the other questions I posted, that would help us to help you.

Good luck!

Stan KC7XE.

Hi Chris.?

I use three dipoles and switch manually between them. I have a Z Match tuner that gives me most every band from 40-10 with this setup. It is very primitive. All manual.?
I trip the SWR protection when I fail to swap antenna feeds or fail to preset the tuner. I get the magic S on the display. I can reset the trip by simply activating then exiting the menu. However the rapidly fluctuating SWR will be present when I drop into the Hardware menu to retune my new antenna setup. The SWR readout is essentially useless. ?
If I power down then back up the SWR readout in the Hardware menu works fine?

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73

Dick

W4PID?

I recently experienced the "Oscillating SWR" issue too. The 2 least significant digits of the SWR display were rapidly changing. This followed an SWR protection trigger. My QMX LB was factory assembled about a year ago so we can probably rule out assembly errors. It happened to me before I became aware of this forum thread so I have not tried any of the remedies suggested. My QMX is running firmware version 26. I will watch for repeats of this condition and note what I need to do to clear the problem. It's a minor flaw in an otherwise fine radio.

My personal experience is that the SWR oscillations occur while the rig is actively in its SWR protection state (meaning the S is shown on the main screen—even if you can’t see it—due to accessing other radio menus and functions), or in the CW practice mode state.

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In order to clear the S, you not only need to enter a menu, but also completely exit out of the menu hierarchy and land back on the main screen. It’s tempting to notice that the protection triggered (or even first noticing something in your setup that could’ve triggered it—like an unmated connector or fallen antenna), and go straight into the Hardware Tests… but that alone won’t clear the protection state.?

Garrett

pp5/KC3UNP

I seem to have the same issue. I am using a Commercial Broadband Dipole up about 6 metres that is low SWR on all bands.

The antenna is fed with around 20M of RG213 then 5M of RG58, there is an RF choke just before the operating end & the operating area is under an earthed tin roof. So stray RF should not be an issue.

At random intervals the QMX+ (less often with the QMX high & Low band units - but still happens)? decides to find high SWR & the dreaded "S" appears on the display

The antenna analyser shows well under 2:1 but the QMX will have a rolling SWR value (as per attached video).

Sometimes entering "Settings" and exiting will fix it, often powering off & on will return to normal operation.

Best thing seems to be to change to another rig & go back to the QMX some time later.

It can be very annoying when you know the antenna is fine.

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Cheers

Rob

VK5ZIK