An Alternative Pixie Known as The AP 80

Overview

The project is an improved design of the Pixie which originally consists of an LM386 audio amp and just two transistors.

Explanation

The design of the circuit is very straightforward although it looks like complicated. A Colpitts crystal oscillator is the start of the circuit which uses a trimmer cap and 2N7000FET to provide a 600Hz frequency shift by adjusting the trimmer cap. Using a real mixer is the only way to fix the deficiencies of the Pixie. The transmitter low pass filter and receiver input is coupled with a classic series tuned C/L with diode limiting. The lower impedance input from the QSK network is coupled with the receiver input tuned circuit high impedance.

The transmitter is powered by 12V 1W supply as it consists of a 2N2222A buffer amp and a 2N7000. The Ac signal is kept coupled to the gate by the diode across the 2N7000 base. A PNP 2N3906 is added to the circuit to provide standard active low keying.

The receiver offset is the most critical adjustment which uses the C25 trimmer for control. The Rx inout trimmer is adjusted for best signal by attaching an antenna.