IT 104 – Lab 7
Frequency Response
Objectives
This lab will illustrate the frequency response of simple low-, high- and band-pass filters. To
enable the effects to be easily seen over a wide range of frequencies, log plots will be made.
Equipment Required
DMM, oscilloscope, function generator, resistors, capacitor and inductor.
Procedures
1. For the circuit of Figure 1, develop the transfer function,
VR
. Draw the magnitude Bode
VS
plot for this function. Center the Bode plot at the breakpoint frequency.
2. Connect the circuit of Figure 1. Pick frequencies that correspond to points of interest on
your bode plot, and measure the voltage across the resistor at these frequencies.
Convert these measurements to gain (in dB), and plot them on the same semilog paper
that you used for the Bode plot. What type of filter is this?.
3. Change the capacitor in the circuit of Figure 1 to a 27mH inductor. Measure the
resistance of the inductor and use it in all calculations. Repeat procedures 1 and 2 using
a new sheet of semilog paper. (Hint: remember to include the internal resistance of the
inductor in your calculations.) What type of filter is this?
4. Connect the circuit of Figure 2. Calculate the resonant frequency. Measure the voltage
across the resistor at this frequency. Is it larger at this frequency than at any other
frequency? Find the bandwidth and Q of the circuit by measuring the frequencies at
which the voltage drops to the half-power point at either side of the resonant frequency.
Signoff
Signoff consists of showing your plots to the TA.
Results and Conclusion
Compare the expected to the measured values. Make observations about the appearance of
the plots. What is the slope of the lines for various regions of the plots?
27 mH
0.1F
0.1F
1 k
4 VP-P
Figure 1
100 
4 VP-P
Figure 2