QRP TRX by RA3AAE

A minimalistic direct-conversion CW transceiver with output power around 1 W at 50 Ohm load. The source and 50 Ohm resistor on the left represent an antenna. The pushbutton is the telegraph key. When key is pressed, the two MOSFET's stage operates as a frequency doubler and power amplifier. When key is open, this stage works as a mixer. The 10 nF capacitor at the base of BJT in the local oscillator stage can (and should) be replaced by a suitable crystal resonator to stabilize the LO frequency at half of the main band frequency. You can use a transformer from an old radio at the output of the low-frequency amplifier stage with low-impedance earphones (32 Ohm resistor) or replace it all together by high-impedance earphones (but not the piezo ones!)

published 1 year ago