The RF Power Meter 2 is a development based on the utility of RFPM1, but it shares nothing with the RFPM1, save using an AD8307 as the sense module.

Design criteria
The design criteria are:
- small, portable, battery powered;
- direct reading dB scale;
- flexibility for a range of adapters to measure power, current etc;
- local display including bar graph, time, and dB value;
- log measurements to a serial port of some kind;
- offer remote access for recent measurement log.
Design outline
The RFPM2 uses an AD8307 log power detector to obtain a analogue ‘DC’ voltage proportional to the log of the input power. The input port is 50Ω SMA, and accommodates from about -75dBm (the noise floor) to +15dBm.
The analogue output of the AD8307 is digitised on a microcontroller board, a NodeMCU which uses an ESP8266 processor with integral WiFi. The board also contains a CP210x USB to serial adapter for programming, power, and serial logging.

The display is deliberately generic, the units are dBm at the SMA input, but they could be dBA with a suitable current probe, or +xx dBV/m with a field strength sense antenna. Continue reading RF Power Meter 2 (RFPM2)
Last update: 8th December, 2018, 8:16 AM