Lab 5 - RF Amplifier
In this experiment, I simulated, built, and tested a RF amplifier that would boost the weak AM signal coming into our radio. The RF amplifier is a fairly simple circuit consisting of a common-source and common-emitter amplifier.
Before constructing this in the lab, simulations were conducted using LT Spice software. Simulated data was then compared to actual data acquired in the lab.
The RF amplifier ended up providing a necessary gain for our team's radio and allowed the radio to function.
Figure 1 - Completed Radio Circuit with RF Amp
For the first part of the lab, the common-source amplifier was constructed. To start, the Q-point and voltage gain of the amplifier was determined for multiple load resistance values. This data is shown in Table 1.
Next, I added the RFC inductor to increase the gain of the circuit. Voltage gain results with the RFC inductor are also shown in Table 1.
Table 1 - CS Amp Q-point and Gain
Table 2 - RF Amp Gain
For the next part of the lab, I added the common-emitter amplifier to the common-source amplifier. With the RF amplifier constructed, I measured the Q-point of the BJT transistor, which is shown below:
Q-Point = (1.86V, 3.86mV)
Also measured, were gain values for different load resistances of the amplifier circuit. These can be found in Table 2.
For the final part of this lab, I connected the RF amplifier circuit to the input of my detector of the radio circuit. Using the function generator to suppy an AM signal, I analyzed the output of the radio on the oscilloscope and observed a decent gain of around 4V/V. This can be seen in Figure 2. At lower input amplitudes, the gain was better, but had a large clipping effect on the output.
Using an existing antenna, I tried to pick up a signal with my team's radio, but only heard static noise. I remain optimistic that I will pick up a signal next week using an antenna built to our team's specifications.
Figure 2 - Output of Radio Circuit