Digital Power and SWR Meter
Project updated 29.01.2004
I started to experiment with HF FET amplifier. Amplifier project is not yet ready but this SWR meter diversified off from it. Amplifier controller is going to include this SWR meter and other bells & whistles. While doing my amplifier controller I found that separate digital SWR meter would be also nice project. After few tries how to build Measurement Bridge for 1,6 to 28 MHz range basic ingredients for meter was ready. This 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). This is experimental project and you can modify code as you wish. In the future I may also add some features to the software.
Digital Power / SWR meter for HF use
Building the meter
Donít try this project if you do not know what you are doing. I have no possibilities to provide any help.
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 fromMicrochip errata pages.
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 herehttp://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 SWRbridge prototypes and component side
SWRbridge pc board
Display unit is build around Microchip 16F877A processor and Solomon LM1125SYLU1 LCD display. LCD displays you can buy from Mattioh2mh@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.
Display unit pcb picturetop and bottom side. LCD contrast trimmer is missing in this picture.
Display unitlayout top side and bottom side. Note few jumper wires required.
Display unitpc board
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.
Softwaresource code can be found here
Ready to load HEX code for16F877A
Ready to load HEX code for16F877
Picture of basicpower and SWR display
Picture offorward / reflected power bar display
I would thank ham fellows Jussi OH7TE, Matti OH7SV and Tane OH2UG for their time and valuable ideas. Fellows have been good "resonator" for me while discussing problems and solutions.
Matti OH2MH supported the project with LCD display module. Matti may be good source also for you.