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What you are hearing is interference from the short data burst to your radio. I have been plagued by this from the QLG1 through 2 to QLG3. I have reduced it, but never eliminated, over a period of time with various additions of total rf screening (copper tape around except antenna), additional 100pf caps across all outputs, ferrite blocks both end of cable, screened cables, not just plain wiring, separate 5v supplies for QLGs, not fed from QDX etc supply, improving electrical contact between radio anodised panels also. It all helps.
73 Ken g4apb?

Hi Steve,

I am experiencing the same thing. It starts on 20 m and gets progressively ?louder until
so loud on 50 MHz, that band is unusable. I suspected the gps module as another reply
suggested ?but have not yet removed it to confirm. ?I hope someone has a fix for this.

Dave

Ian, Ken and Dave

Thanks for your comments confirming I'm not imagining hearing things!

Ive looked at the data line on the QLG3 and I see a short burst of data every second, but cant imagine that this is the source of what I'm hearing i.e. long periods of what appears to be a pure sine wave around 700Hz, I can also hear a similar pattern but much higher in frequency, 5000Hz maybe, in the background.

The fact that these signals cant be tuned by the VFO suggests to me that the signal is not being processed in the same way as receiving a signal off air, it seems like it is getting into a stage much later.

In Hans' recent YouTube video, he says that the receiver is not strictly a direct conversion as in the QCX, but has an IF of 12kHz implemented in the audio chain, achieved in the magic of the firmware. I wonder if the interfering signal is getting into the system at this stage.

I wonder if the QLG3 is generating signals internally in the range 0-48kHz which are getting into the audio system at the 12kHz IF frequency? I dont have a spectrum analyser, but would be interesting to see.

Ken, I wonder if you have only experienced this on the QMX/QMX+ ? you mentioned that you have experienced this? problem with the QLG1 and QLG2, both of which preceded the QMX.

Perhaps this is just a minor annoyance at the moment, but can see it becoming a significant problem as the firmware is developed.

Maybe the best solution is a toggle switch on the back panel to remove power from the QLG3 until its needed!?

73 Steve G4EDG

Hi Steve,
I don’t have a QMX, but I started with the QLG1 and my U3S tx, and the interference was to my HF rig, the FT897. Lots of ferrite experiments but the unscreened setup I never cured. Then I built the QLG2, same interference so I built it into a screened box, extensive experiments with connector filtering etc gave some improvement, I finally fitted an on/off switch so when on WSPR and all have stabilised, I could turn it off to stop the interference. This one even interfered at 2m. Then I built the QDX and used the QLG3 with the optional screen, used a short as poss connecting leads and ferrite blocks, but I still get some tramlines in FT8 and WSPR MODES if it is left on. I also built a standalone GPS enabled QRPLabs clock (QLG2 I think), but it blotted out my DAB radio when placed close by until I fitted ferrite clamps every couple of inches along the 5v wall mount PSU I use.
If I listen on 2m FM, at the same time as I use any of the kit above, I hears a background pulsing noise every second, so I assume this is the data burst. It is only at 9600 baud so I don’t know why it causes so much grief. If I run my FT896 Cat control at the same baud rate to my PC, I get no interference from that at all. It’s a mystery.
73 Ken g4apb?

I installed a miniature toggle switch in the rear panel replacing the power
jumper on the board. Maybe a better solution will come in the future. For
now I can turn off the noise when not using the GPS.

Dave
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