ECE 3074
Experiment 37: Electromagnetic Interference
Name: ______________________
Date: _____________________
Analysis:
The values of the resistors and capacitors used in the design for the Twin T notch filter are:
R1 = R2 =
R3 =
C1 = C2 =
PSpice:
Insert schematic from PSpice
Figure 1: Twin T notch filter
The results from the simulations of the Twin T notch filter:
Insert plot from PSpice
Figure 2: Trim pot resistance is equal to 33 k.
C3 =
Insert plot from PSpice
Figure 3: Trim pot resistance is equal to 67 k.
Insert plot from PSpice
Figure 4: Trim pot resistance is equal to 100 k.
Table I: Center Frequency, Bandwidth, and Q of the Twin T Notch Filter
Determined from Simulations
Trim Pot Resistance
33 k
Center Frequency
Bandwidth
Q
Measurements:
Part A: Build and test instrument amplifier
Verification that the gain of the instrumentation amplifier is 3.
67 k
100 k
Insert oscilloscope plot
Figure 5:
Part B: System Noise
Figure 6: Spectrum of instrument noise of the Velleman oscilloscope

Figure 7: Spectrum of noise from the instrumentation amplifier

Figure 8: Noise voltage as a function of time from the instrumentation amplifier

Table II: Experimental values of system noise.
Noise
Level (dB)
Oscilloscope
Instrumentation
Amplifier
Part C: Antenna Noise
Maximum
Voltage
(V)
Minimum
Voltage (V)
N/A
N/A
Figure 9: Spectrum of antenna noise

Figure 10: Noise voltage as a function of time from antenna

Figure 11: Spectrum of antenna noise coupled with transformer signal 

Figure 12: Noise and signal voltage as a function of time
Table III: Experimental values of antenna noise.
Noise
Level (dB)
Maximum
Voltage
(V)
Minimum
Voltage (V)
Antenna
Antenna and
Signal
Insert Bode Plot
Figure 13: Trim pot resistance is equal to 33 k.
Insert Bode plot
Figure 14: Trim pot resistance is equal to 67 k.
Insert Bode Plot
Figure 15: Trim pot resistance is equal to 100 k.
Table IV: Experimentally Determined Center Frequency, Bandwidth, and Q of the
Twin T Notch Filter
Trim Pot Resistance
33 k
67 k
100 k
Center Frequency
Bandwidth
Q
Table IV: Percent Deviation of Experimental Center Frequency, Bandwidth, and Q from Simulated
Results Obtained from PSpice
Trim Pot Resistance
Center Frequency
Bandwidth
Q
Conclusions:
33 k
67 k
100 k