I'm glad you were able to solve the noise problem.
Returning to my question, I did not want to influence your answer, so my question was not clear.
was that he attached a conductive layer with glue, which he then insulated with a foil insulator, so that the conductive layer does not cause a short circuit elsewhere. The point is that it was not grounded anywhere, so it created EMI protection.
The person was satisfied with this solution.
Currently, they make a 15 pin to 22 pin flexible cable with EMI protection for the RPi5, but this is not good for us for the RPi4.
I route the power cable through an FT140-43 type ferrite ring. The cable has a cross-section of 2x2.5 mm2 and I made 6 turns on the ferrite ring just before the power connector of the sBitx. You can see a photo of this in my previous message.
One addition: if you use an external keyboard, you can take a screenshot of the keyboard by pressing the Prtscr button. You can find the image as date_time_screen_size_scrot.png in the RPi home folder.
If you are an active radio user, you may need to dissipate the heat produced by the device. Since I use the device a lot, I put a lot of emphasis on this.
In half a year, I made 4800 QSOs in digital modes, so I cool the heatsink from the outside and the RPi from the inside with a fan. Currently, the external temperature here is permanently above 40C, the CPU temperature starts at 38C when switched on and reaches 58C during continuous use. The critical temperature is 80C, but there is no need to worry, because the built-in protection then comes into play and regulates the speed and usage.
Thank you for answering my request. I wish you successful use and lots of joy.
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Gyula HA3HZ
HA3HZ