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QMX+ Low Image rejection at 160m,

 

Hello,
My newly built QMX+ is showing poor image rejection in the test suite, but only when for 160m, other bands look OK.
The image at 160m indicated -3.7, with both wanted and image around -16.
Looking at the Test ADC I/Q, the two signals show almost in phase when they should be 90deg apart for quadrature (other bands show quadrature as expected). The Q waveform is?
only about half the amplitude of the I waveform (again only on 160m, other bands having equal amplitude as expected).
I suspect both the above are different views of the same issue, but I am not sure where to look to further investigate the cause.
Any suggestions appreciated.
Best regards Trevor G6PSZ
?
 

Hello Trevor

160m image rejection is a known issue and I will fix it as soon as I have done the SSB firmware update. It's not a hardware issue, it's firmware. If all the other bands are correct then you don't need to worry!

73 Hans G0UPL



On Thu, Sep 26, 2024 at 3:12?PM Trevor Shackleton via <trevorshackleton=[email protected]> wrote:

Hello,
My newly built QMX+ is showing poor image rejection in the test suite, but only when for 160m, other bands look OK.
The image at 160m indicated -3.7, with both wanted and image around -16.
Looking at the Test ADC I/Q, the two signals show almost in phase when they should be 90deg apart for quadrature (other bands show quadrature as expected). The Q waveform is?
only about half the amplitude of the I waveform (again only on 160m, other bands having equal amplitude as expected).
I suspect both the above are different views of the same issue, but I am not sure where to look to further investigate the cause.
Any suggestions appreciated.
Best regards Trevor G6PSZ
?
 

Thanks Hans,
Great kit with excellent support. I look forward to the firmware updates in due course, appreciating that they take time to develop and test.
As an aside I do wonder if you considered adding thermal reliefs on the ground plane connections (on all layers). From experience they make reliable soldering (and a better chance of successful rework) much easier. I would have thought that the tiny increase in inductance would be insignificant at HF.
73 Trevor G6PSZ
 

Hello Trevor

If you look closely at it with some optical magnification you'll see that there already are thermals. And they're on all layers. Just that with 6 layers and thermals every 90° that means up to 24 thermals per ground point.?

73 Hans G0UPL


On Thu, Sep 26, 2024, 16:42 Trevor Shackleton via <trevorshackleton=[email protected]> wrote:

Thanks Hans,
Great kit with excellent support. I look forward to the firmware updates in due course, appreciating that they take time to develop and test.
As an aside I do wonder if you considered adding thermal reliefs on the ground plane connections (on all layers). From experience they make reliable soldering (and a better chance of successful rework) much easier. I would have thought that the tiny increase in inductance would be insignificant at HF.
73 Trevor G6PSZ

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