Dear Joan & Jzad,
In the meantime, I did another test with the WiFi antenna. By coincidence I have a fitting WiFi antenna with 1 meter of cable (see picture). So I connected this one and was able to have the antenne about 100cm away from the Up2Stream Mini PCB.
My conclusion: no difference, still hum & noise at the same level as with the standard antenna.
So I guess the hum & noise cause must be either in the power supply (ground loop), or in the audio connection between ‘Up2Stream Mini audio-out’ and ‘speaker amplifier audio-in’.
To be continued!
