Hi Lawrence,
Thanks for the suggestion.? I have not investigated the Dorji DRA818 transceiver modules because the specified input voltage is 3.3 - 4.5 volts while the NiceRF SA818 is rated for 3.3-5.5 volts.? SHARI would require a circuit to lower the input voltage of up to 5.2 VDC from the Pi.? In BRIAN I use a series diode to drop the voltage about 0.9 VDC since the BF888S is normally powered by a 3.7 VDC battery.
My examination of the SA818 revealed that there is an internal 3.3 VDC regulator which powers the RDA1846 transceiver IC and the CPU which controls it.? The driver and PA are powered directly from the input voltage.? I am wondering if the Dorji module does not employ a regulator and thus the 4.5 VDC limit because the RDA1846 is specified for 3.3 to 4.8 VDC.? Have you powered the Dorji module from as much as 5.2 VDC (the official Pi 4 power supply output) and/or have additional information as to the Dorji circuitry and input voltage specification?
Steve - N8AR
Steve-N8AR