The British Amateur Television Club "Portsdown 4" Amateur TV Transceiver is based on the Raspberry Pi 4, and we recommend feeding between 5.0V and 5.2V directly on to the GPIO connector.? The +5.1V goes to pins 2 and 4, with ground connected to pins 6 and 9 (you can also use the other ground pins).
These pins are connected directly to the USB-C power input connector, so there is no advantage in using a USB-C cable and plug.? On the Raspberry Pi 3, powering through the USB connector offered extra protection, but this circuitry is not present on the Raspberry Pi 4.
Note that some SDRs are fussy about the exact USB voltage.? The LimeSDR Mini prefers 5.1V or above, while the ADALM Pluto prefers 4.9V to 5.0V.
Dave, G8GKQ
