Digital HF Power-SWR Meter

This power-SWR meter is intended to 5 to 100W ranges but you can build heavier measurement bridge and scale instrument for whatever range you want. Current version of software provides few basic displays. Scaling and other feature setup parameters are in software code (no setup menus).

Features:
Digital Power / SWR meter for HF use

Power range 5 to 100W
Frequency range 1 to 30 MHz
Peak hold display operation for SSB operation.
Few basic displays showing Forward, Reverse, net outgoing power and SWR
Dual bar graph display for forward and reverse power
Large and clear 2*16 character LCD display
Simple two button interface
Hi SWR warning and alarm LEDs
Separate display and SWR bridge units. No antenna cable routing to meter.

Building the meter
You can build and test SWR bridge and meter part separately. SWR Bridge can be tested with volt meter and display unit with 0 to 10V psu. Remember that high power RF radiation softens your head. No ready-made PCBs are available. Beware faulty Microchip 16F877A parts. You can read more from Microchip errata pages.

SWR bridge
Critical component is transformer L1. L1 is 10 turns bifilar wound on Amidon FT50-43 core. First twist two 0,4mm wires together and then wind 10 evenly distributed turns on core. Primary (TX to antenna) is just wire going through the core. Wire can be just straight wire or thin coax other end of the braid grounded. You can buy Amidon cores here http://www.srat.fi . For safety reasons and for better performance it is wise to install SWR bridge board into metal enclosure. You can find SWR bridge theory from ARRL handbook.

Picture of SWR bridge prototypes and component side

SWR bridge pc board
SWR bridge schematics
SWR bridge layout

Display unit
Display unit is build around Microchip 16F877A processor and Solomon LM1125SYLU1 LCD display. LCD displays you can buy from Matti oh2mh@sral.fi . Microchip 16F877 (non A version) is also supported but without LCD backlight control. Only critical components on display board are resistors R2,R3,R5,R6 and IC2. Display unit PCB is designed so that you can separate push button switches and SWR warning LEDs if your enclosure selection requires this. Back light current generator fet Q2 may require additional cooling if operating voltage exceeds 10 VDC.

LCD contrast trimmer is missing in this picture

Display unit schematic
Display unit layout top side and bottom side. Note few jumper wires required.
Display unit pc board

Software
Project is done with Hi-Tech PICC compiler. Not strictly ANSI C but with some work project can be transferred to other environment. This first test version does not include any user setup functions. All setup and calibration variables are in software code. Displays are not carefully planned they just show needed basic information. Things may improve in the future.

Software source code can be found here
Ready to load HEX code for 16F877A
Ready to load HEX code for 16F877

Picture of Basic Power and SWR display - Forward/Reflected Power Bar Display