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16.5: Procedure

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  • 1. Using Figure 16.4.1 with Rs = 100 k\(\Omega\), Ra = 2.2 k\(\Omega\), L = 10 mH, Rcoil = 7 \(\Omega\) and C = 10 nF, determine the theoretical resonance frequency and Q, and record the results in Table 16.6.1. Based on these values determine the upper and lower frequencies defining the bandwidth, \(f_1\) and \(f_2\), and record them in Table 16.6.1 also.

    2. Build the circuit of Figure 16.4.1 using Rs = 100 k\(\Omega\), Ra = 2.2 k\(\Omega\), L = 10 mH and C = 10 nF. Set the output of the generator to a 10 V p-p sine wave at the theoretical resonant frequency. The large value of Rs associated with the voltage source will make it appear as a current source equal to approximately 100 \(\mu\)A p-p, assuming the parallel branch impedance is much less than Rs. Place a probe across the parallel branch. Set the frequency to the theoretical resonance frequency of Table 16.6.1. Make sure that the Bandwidth Limit of the oscilloscope is engaged for both channels. This will reduce the signal noise and make for more accurate readings.

    3. Adjust the frequency in small amounts, up and down, until the maximum voltage is found. This is the experimental resonant frequency. Record it in Table 16.6.1. Note the amplitude. Sweep the frequency above and below the resonance frequency until the experimental \(f_1\) and \(f_2\) are found. These will occur at a voltage amplitude of approximately 0.707 times the resonant voltage (i.e., the half-power points). Record these frequencies in Table 16.6.1. Also, determine and record the experimental Q based on the experimental \(f_0\), \(f_1\), and \(f_2\).

    4. Transcribe the experimental frequencies of Table 16.6.1 to the top three entries of Table 16.6.2. For all of the frequencies in Table 16.6.2, measure and record the voltage across the parallel branch.

    5. Based on the data from Table 16.6.2, plot the parallel branch voltage as a function of frequency.

    6. For high Q, change Ra to 10 k\(\Omega\) and repeat steps 1 through 5 but using Tables 16.6.3 and 16.6.4.