[arm-allstar] arm-allstar Digest, Vol 8, Issue 2

[Ken]

"The audio distortion is noticeable on audio from the node. (transmit audio)
To eliminate/isolate the issue I swapped out the URI for a SYBA USB Audio
FOB and PC speakers.
Still the same background hum/distortion. So that eliminated RF
interference, ground loops, the URI and the radio.
"

Not at all.  Both the URI and essentially all cheap-o fobs connect the
negative side of the 5 volt supply from the USB port though to the audio
common.  If you have one 5v supply to the BBB, another one to the hub/fob
and (of course) a power supply to the transmitter,  you have lots of
opportunities for ground loops.  Some wall-warts (with 2-wire connections to
the ac line) have been known to superimpose up to 50 volts AC on the DC
common (though a high impedance leakage path).

An isolation transformer (on both tx audio and rx audio)  would break the
loop.  I have found that a short heavy wire from the transmitter chassis to
the computer case/chassis  fixed this kind of problem for me problem at
no-cost.  But I am not exactly sure where the "chassis ground" of the BBB is
;-)

GL
Ken