Bandpass Filter

The purpose of this lab was to introduce the tank circuit as a bandpass filter and become familiar with bandwidth and Q of a resonant circuit.

First, we were instructed to build the circuit in Figure 1. Next, the function generator was used to provide a variable frequency input signal. The dual trace feature of the oscilloscope was used to observe the input and output signals simultaneously.

Figure 1: Tank Circuit Schematic

The oscilloscope was used to measure the resonant frequency and the low and high frequencies. The resonant frequency was determined by locating the peak value on the oscilloscope. The peak value on the oscilloscope can be seen in figure 2. Next, the low and high frequencies were determined by subtracting and adding 3 dB. This was done using the cursor feature of the oscilloscope. The results are listed in Table 1. Next, Rs and RL was replaced with a 1 kOhm resistor. The results are listed in Table 1.

Figure 2: Resonant Frequency

Table 1: Measurement Data

In conclusion, this lab introduced me to using the tank circuit as a bandpass filter and I gained experience in using features of the oscilloscope to determine resonant frequency and calculate Q. Both resistor values produced about the same resonant frequency but the 1 kOhm resistors provided a lower bandwidth which therefore produced a higher Q. Higher Q is ideal so the circuit with the 1 kOhm resistors will be used in future testing.