How does a pixie radio work?

Descriptions

The Pixie radio is a simple and compact amateur radio transceiver that operates on a single band with low power output. The Pixie works by using a simple circuit consisting of only two transistors and a handful of passive components.

The first transistor in the Pixie is connected as a 7 MHz crystal oscillator. The crystal provides a stable frequency reference for the transmitter and receiver. The transistor is biased to oscillate at the frequency of the crystal, which is 7 MHz in this case. This oscillator is continuously on to generate the carrier signal on transmit and to provide the local oscillator for the receiver.

The second transistor in the Pixie serves as the RF final amplifier on transmit. When the Pixie is in transmit mode, an audio signal from a microphone or other audio source is fed into the base of the first transistor. This modulates the carrier signal generated by the oscillator, and the resulting modulated signal is amplified by the second transistor to produce a low power output signal for transmission.

On receive, the second transistor in the Pixie acts as an amplifier for incoming signals. The oscillator signal is mixed with the incoming signal to produce a low-frequency difference signal, which is then amplified by the transistor. This process is known as direct conversion or homodyne detection, and it allows the Pixie to receive signals at the same frequency as the transmitter without the need for a separate local oscillator.

Overall, the Pixie radio is a simple but effective design that demonstrates the principles of crystal oscillators, RF amplifiers, and direct conversion receivers. It is a popular choice for beginners and experimenters in the amateur radio community who want to build their own radio equipment and learn more about radio technology.