50 Ohm Dummy Load Extension #dummyload #power meter #dummyload #power


I recently built the 50 Ohm 20 Watt dummy load from QRP-Labs. It works well with very close to 50 Ohm on most of the ham frequency spectrum. But I was not satisfied by the fact that I need a voltmeter and a calculator when I want to use the power meter feature in the dummy load. So I grabbed my parts box and built a power meter extension. It can measure instant power, peak power and average power over about 2 minutes, selectable with the rotary encoder knob. Press it to reset the peak value detection. It is built with an Arduino Pro Mini 5 Volt, a .91 inch OLED display and a 16 bit AD convertor ADS1115. The battery is a rechargeable 9 Volt type, good for about 24 hour of run time per charge. The software does linearization by interpolation between set points to compensate for the non-linear characteristic of the power sensor diode. I plan to extend the program to add a calibration feature for all ham bands form 160 m to 70 cm and store the set points in the EEPROM of the Arduino. I will see how far up in frequency I can go with the built in 1N4004 diode in the dummy load. The enclosure is from Amazon. 

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