ELEC3030 Lab 9: Oscillator

In this week's lab activity, I studied the last component of the mixer: the oscillator which produces a sinusoidal output that is delivered to the emitter of the mixer circuit (from Lab 8). As mentioned in the previous post, the oscillator is responsible for producing a frequency which will be subtracted from the carrier frequency to achieve the desired radio frequency. The following exercises document my study of the oscillator circuit.

Figure 1: Oscillator Circuit

First, I constructed the Hartley Oscillator shown in Figure 1. Adjusting the trimming capacitor (Ctrim), I observed the frequency spectrum changes in the output via the oscilloscope. As I inspected these changes, I determined the frequency range of the circuit (results in Table 1). At the lowest achievable frequency, the output (Figure 2) is almost a perfect sine wave, which is the desired output. However, at the highest frequency, the output (Figure 3) is more distorted, so it is evident that the circuit will perform better at the lower end of the frequency range.

Table 1: Frequency Range of Oscillator Circuit and Comments on Output Sine Wave

Figure 2: Output of Oscillator Circuit at 1 Mhz

Figure 3: Output of Oscillator Circuit at 1.7 MHz

Finally, after having constructed all the necessary parts of the mixer circuit (bandpass filter, mixer, and oscillator), I now can integrate it into my radio. However, as I have mentioned previously, I do not intend to use the mixer because I am pleased with my radio. At the beginning of this semester, I never thought that I would have the opportunity to learn how to construct a home-made radio that actually works. I am thrilled to have accomplished such an engineering feat. This is definitely an achievement to put on a resume and it has given me ideas for more electronics projects involving RF devices.