1Getting the initial idea from W1GHZ’s published project, I decided to homebrew the power/phase ratiometer using a microcontroller so as to simplify the analog circuitry. The final result is a relatively small standalone device with N type connectors (2 cell 400mAh lipo battery included!). Two way serial communication is provided via an 8 pin mini-DIN connector which doubles as a charging connector for the battery. The display is a common 2×16 character LCD. A three position switch is the only control. Position one is power off, the other two positions switch the display between measurements displayed in dBm/ degrees and in raw ADC values (the ATMEGA16’s internal ADCs are used). A metal internal chassis is used to mount the various components (connectors, screen, PCB etc.). The RF section is built inside a shielded metal enclosure. Two SMAs connect it with the N type connectors via RG402 coaxial cables (which are exactly same length). Electrical connections for power and signals are via feedthrough capacitors. The AD8302 (relative measurements) and LT5534 (does absolute power measurement on connector 2) are mounted on the RF PCB. An ICSP port is also included for microcontroller programming. The 5 volt regulators used are low dropout type (one for the LCD backlight and one for all the rest). The black painted plastic enclosure is commercial. The performance is: 50dB dynamic range (-50dBm to 0dBm) from 50MHz to 2.7GHz.


The connector end. The mini-DIN connector is between the two N type connectors.


General internal view.


The two cell 400mAh lipo battery is visible under the screen.


The RF PCB is visible. The AD8302 is on the middle and the tiny LT5534 is on the left.