RF Systems Lab

Lab 5: RF Amplifier

5.1 RF Amplifier

An RF amplifier is needed to boost the weak AM signal received by the antenna prior to audio signal extraction by the detector. Our RF amplifier will

consist of two stages as shown in Figure 5.1. The first stage is a common source (CS) amplifier based on the field effect transistor, or FET. The CS amp

features high input impedance so most of the weak signal will appear across the input terminals, but suffers from a fairly small gain. To increase gain,

the second stage is a common emitter (CE) amplifier as studied in Chapter 2.  The pre-lab report for sections 5.1-5.4 can be found below.

5.5 RF Amplifier Construction

The common source amplifier is constructed with load resistance 10kΩ, and the Q point and gain are measured. Then, the measurements are repeated for load resistances 1kΩ and 1MΩ. Then, an RFC is added and the new gain values are recorded for all three load resistance. The results are shown below in Table 1. Then, the common emitter amplifier is added to the circuit and the Q point for the npn BJT is recorded to be (1.21V, 3.22mA). The gain is then recorded for the new circuit at 100Ω, 1kΩ, 10kΩ, 100kΩ, and 1MΩ and the results are recorded in Table 2. Figure 1 shows the plot of this data. 

Finally, the RF amp is connected to the radio, and various AM inputs are tested to demonstrate functionality.