Lab 08: Mixer

In an AM radio, the Mixer multiplies the input RF signal from the antenna with a local oscillator frequency in order to produce signals at different frequencies. In this lab, I built a mixer circuit and tested it in several conditions to determine its performance.

To start, I built the circuit following the circuit diagram included in the lab as displayed in the picture above. After using the function generators to provide the oscillator and RF signal inputs, I observed the FFT of the output on the oscilloscope in order to determine the difference frequency. I then repeated the experiment with an RFC placed between Rc and the collector of the transistor.

While I had a hard time getting my mixer circuit to operate properly initally, I was able to determine the difference frequency of the circuit. Adding the RFC increased the performance of the circuit noticeably, with a clearer output signal and a more definite difference frequency of around 200 kHz.