Oscillator
An oscillator is a circuit that oscillates, thank you for coming to my TED talk.
An oscillator is a circuit that takes a DC input and converts it to an AC output. For the radio design, a sinusoidal signal is needed for the mixer, the oscillator can ben helpful when there is no AC signal to attach to the mixer. For instance, in a portable radio that operates with batteries, the oscillator can draw power from the batteries and feed the AC signal to the mixer.
Hartley Oscillator
There is many configurations for building an oscillator, the one discussed here is the Hartley oscillator. The Hartley oscillator features a capacitor in parallel with two inductors and the frequency of oscillation is dependent on the magnitude of each. However, inductors are hard to tune and change their values, and is frankly inefficient, thus, the capacitor is tuned in the circuit to achieve the desired frequency. As seen in figure 1, the trimming capacitor can be tuned to reached the desired frequency.
Figure 1: Hartley oscillator implemented
From figure 2 and figure 3, it is clear that the output signal is not a clean sinusoidal signal. The low frequency is at around 1.2 MHz and high frequency at 1.5 MHz, the low frequency has more noise or disturbance than the high frequency.
While the circuit did not work as intended during implementation, some adjustments could be done to make it produce a better sinusoidal wave. Such adjustments would be changing some of the resistance values, or changing the capacitance before the output, which should block the DC signal and only allow AC to pass. (filter the filter?)