While this thread is about low voltage there is a related issue if using the RPi for transmitting.
In setting up my RPi v1 for WSPR TX I found that the 5V from several of my switching wall warts was far from pure DC. I discovered this because my WSPR TX signal was full of close-in sidebands - a very dirty signal, and additional filtering of the 5V was unable to clean the signal up. Problem solved by using my one switching wall wart (a 2.4A DVE brand) that produced nice clean DC.
Tom??? K4ZAD
