Lab 09: Oscillator

The heterodyne uses a local oscillator generating a constant frequency and multiplies it with the input RF signal in order to filter out unwanted signals and pick up certian AM stations. In order to maintain oscillation, the loop gain must be at least 1 and the feedback signal must add to the original signal, in intervals of n2(pi) radians.

In this lab, I constructed a circuit based on the circuit diagram shown below. After construction, I observed that the frequency range of the oscillator ranged from just under 1 MHz to around 1.7 mHz. The sine wave for this circuit had a lot of distortion on the low end, meaning that the oscillation was probably not a clean signal.

In order to improve the function of the oscillator and cover the radio frequencies I wanted to recieve, I followed the suggestion of the lab manual and replaced R1 with a 4.7k Ohm resistor, replaced Re1 with a 3.3k Ohm resistor, and added Re2 between Re1 and the emitter of the transistor. After making these changes, the operation of the oscillator improved, covering a range from just under 1 MHz to 1.9 MHz. This improvement allows the heterodyne radio to operate over a wider range of inputs and recieve more AM radio

stations.