Guido ten Dolle Turns the QCX CW Radio Kit Into an Arduino-Powered Single Side-Band Transceiver

Radio amateur Guido ten Dolle has released an open source, Arduino-powered upgrade for the popular QRP Labs QCX 5W continuous wave (CW) transceiver kit — turning it into a fully-functional, though experimental, Class-E single side-band (SSB) transceiver.

Designed to provide a low-cost platform for continuous wave (CW) radio work, QRP Labs' QCX is a popular kit — but ten Dolle's upgrade opens up a whole new world. "With this setup I have been able to make several SSB contacts and FT8 exchanges across Europe and so far this experiment is working reasonable well," ten Dolle writes. "It can be fully-continuous tuned through bands 160m-10m in the LSB/USB-modes with a 2200Hz bandwidth, provides up to 5W PEP SSB output and has a software-based full Break-In VOX for fast RX/TX switching in voice and digital operations.

"This experiment is created to try out what can be done with minimal hardware; a simple ATmega processor, a QCX and a bit of signal processing to make SSB in an artificial manner. It would be nice to add more features to the sketch, and see if the QCX design can be further simplified e.g. by implementing parts of the receiver stage in software."

The modification is part hardware, part software. The hardware side is an ATmega328 microcontroller, with an Arduino sketch loaded to sample the input audio and reconstruct the single side-band (SSB) signal by making small frequency changes via an I2C connection to a phase-locked loop (PLL). "In this way a highly power-efficient class-E driven SSB-signal can be realised," ten Dolle notes. "A PWM driven class-E design keeps the SSB transceiver simple, tiny, cool, power-efficient and low-cost (ie. no need for power-inefficient and complex linear amplifier with bulky heat-sink as often is seen in SSB transceivers)."

PCB layouts, assembly guides, and the sketch itself have been published to GitHub.