I noted some online discussions where some people had troubles with the displayed forward and reverse RF power values, and the calculated SWR.
Some of the reports indicate non-zero RF power values displayed when the transmitter is off, symptoms which direct diagnosis in the first instance to review of the ADC input circuit.
This article reviews the hardware design based on documents as published at the date of this article.
ATmega328P datasheet
Let’s start by reviewing some relevant parts of the ATmega328P datasheet.
Above is a simplified schematic of the ADC pin input circuit. Note the current sources IIH and IIL. Continue reading (tr)uSDX – review of the directional coupler ADC design