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 Amateur Radio Frequency Measurements:


 0-30MHZ RF Power Measurement:


 QRP Dual Channel LCD 10W HF SWR Meter USB


Project by:

Antonio Alfinito / I2TZK

Frank Dziurda / K7SFN 

Dinesh Gajjar / VU2FD


Dual Channel LCD SWR Meter SWM2 and SWM3-USB were a great success. Hundreds of Radio amateurs built it these projects with success. With more and more feedback pouring-in and many demanding an SWR Meter exclusively for QRP users, 10W range, USB/Battery Powered, etc, Tony/I2TZK decided to go for a scale down version of PIC18F4550 for this project. 

SWM3-QRP is an USB or Battery Powered CPU. Based on Microchip's PIC18F4550 40DIP Chip, all what that we require is single PIC Microcontroller. 

This new QRP SWR Meter is developed keeping in mind demand of QRP operators looking for a small, power efficient, stand alone SWR meter for 10W class HF Radios. This project fulfills that objective.

At present, only HF bridge is tested and supplied with kits but there is a special space left on main board to accommodate future expansion of a VHF bridge. 

Firmware for SWM3-QRP Dual channel LCD SWR Meter presented here is developed by Antonio Alfinito / I2TZK for the ham community which is basically, a scaled down version of full SWM3 -USB firmware. Tony has removed following capability of original firmware to match this hardware: 1. No PC Connectivity 2. No Configuration of PIC Parameters thru PC

Purpose of this project is to encourage radio amateurs to build their own SWR Meter at a low price.  

I2TZK PIC 18F4550 Firmware V1.0 for SWM3-QRP has:  

Simple, single Micro Controller with built-in A/D converter (PIC18F4550)
Dual channel of Power Measurement. (Only one channel is used in hardware of this project: HF Bridge)
Dual Power: USB or 9V Battery
CPU Unit has:
2 x 16 LCD with Back light control  
Stable Reference voltage.
Built-in HF 10W Balanced Bridge
SWR, FWD, POWER and Actual Power to antenna   calculations/Display.  
Bargraph mode for SWR & Forward Power  
9V Battery Holder on main board
Front panel selection of USB or 9V battery operation

Project Bases:

Project is developed on Three Double-Sided PTH boards. The first one is CPU board where LCD, Regulator, Battery, HF Bridge and Back Light Controllers are located. This board is powered by 5V from either USB or internal 9V battery.

The second board is HF Balanced Bridge. Its a simple Dual Hole Core type passive balanced bridge for 10W.  

Third board is for Front panel push buttons and ON/OFF and USB/Battery Switches.

BNC PCB Type of connectors are used for HF and there is a place available for second pair of BNC for future addition of a VHF Bridge.  

Kit is intended for experienced Radio Amateurs. 

Although, rated at 10W HF, this meter & bridge may work  at higher RF Power. There is always a possibility to flash SWM3 firmware into SWM3-QRP PIC to get PC connectivity and ability to configure this CPU for your own specific purpose. 

A simple powder coated case for this project is supplied with kits. 


 Completed SWM3-QRP with 10W HF Balanced Bridge:

Click the image to enlarge

 HF Balanced Bridge for SWM3-QRP:

Click the image to enlarge

 SWM3 Schematics, Tech Details & Parts List:


SWM3-QRP-CPU Tech Info Doc. 0-500MHZ RF Sensor Document
SWM3-QRP-CPU Schematic & Parts List 0-500MHZ RF Sensor Document
SWM3-QRP-CPU Schematic JPG
SWM3-QRP-10W HF Balanced Bridge Schematic





 SWM3 PC Software, Firmware and Documents
I2TZK Web Site


SWM3-QRP Firmware V1.0 for PIC18F4550

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SWM3-QRP-Kit with 10W HF Bridge  Please Consider SWM3 or SWM4
SWM3-QRP Kit Parts(CPU) List
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