Test and Measurement

The purpose of lab 1 was to become familiar with lab test equipment, generate and measure sine waves, become familiar with amplitude modulation, and generate and measure an AM signal.

For part 1, we were to use the 3311A function generator to produce a 1 V amplitude 10 kHz sine wave and view it on the TDS2022 scope. I started off by powering up the 3311A and TDS2022. Next, I turned the amplitude on the 3311A fully counterclockwise, pressed the 10k range button, selected the sine wave function, and rotated the dial to 1. Next, I connected the 3311A to the TDS2022 using the BNC-to-banana adapter. I pressed "AutoSet" on the TDS2022 and then followed the instructions t average the data to sharpen the signal. Next, I adjusted the 3311A amplitudee to achieve a 1 V amplitude. Finally, I activated the cursors to check the voltage. Figure 1 shows the 10 kHz sine wave generated by the 3311A displayed on the TDS2022.

Figure 1: A 10 kHz sine wave generated by the 3311A displayed on the TDS2022

Next, we were to disconnect the frequency generator from the scope and set the Omega HHM90 digital multimeter (DMM) to read 20 V AC and probe the output of the function generator. The expected voltage was 1 V but due to Vrms = Vpeak/(2^1/2), the voltage was 0.68 V. The DDM measures RMS. Next, we were to use the BK Precision 4040 function generator to produce a 1 V amplitude 10 kHz sine wave. I repeated these steps using the BK Precision 4040 generator.

For part 2, we were to use the BK Precision 4040 function generator to create an amplitude modulated signal. The generator frequency was changed to 1 MHz, an internal amplitude modulation was employed, and the '% modulation' knob was rotated about 1/3 of a revolution from full counterclockwise. The "Sec/Div" knob was set to 250 us so that the amplitude modulated signal could be observed. The results can be seen in Figure 2.

Figure 2: An amplitude modulated wave with approximately 50% modulation

With internal modulation, you are limited to a 1 kHz signal. To get around this limitation, we can use the 3311A function generator as an external modulation source. The scope was used to obtain a 2 kHz, 2 V amplitude signal from the 3311A. This was fed into the VCG/Mod Input connection. The modulation Ext/Int button was changed to the "Ext" state, the Sec/Div knob was set to about 100 us, and the amplitude knob on the 3311A was slowly adjusted until I got a 50% modulation. See figure 3 for the results.

Figure 3: 50% modulated AM signal generated using external modulation

For the last part of this lab, we were to use the oscilloscope's built-in fast Fourier transform feature that allows viewing the spectrum of the signal. First, I connected the 4040 generator output to the scope input, adjusted the generator to a 50 kHz sine wave, and pressed "autoset". Next, I turned on internal AM modulation, rotated the % Modulation knob to about the 10 o'clock position, and adjusted the time base to achieve 'M 500 us'. I used the trigger to measure the maximum (500 mV) and minimum (220 mV) amplitudes. I then adjusted the generator output and the % modulation to achieve 100 mV maximum amplitude and 50 mV minimum amplitude. Then, I pressed the "Math Menu" button and selected operator "FFT", adjusted the time base knob to 12.5 kHz, and adjusted the horizontal position to center the main peek, and changed the "FFT Zoom" to "X 10". Next, I pressed the "cursor" button, chose source "math" and type "frequency", and located the frequency location of the carrier and the two AM sidebands. See figure 4 for the results. The frequencies are recorded in Table 1.1. I changed the cursor type to 'magitude' and determined the level in dB of the carrier and two sidebands. The dB levels are also recorded in Table 1.1. The recorded dB levels were to be converted to voltage amplitudes and recorded in Table 1.1. Finally, I repeated these steps and adjusted for 100% modulation. The results for 100% modulation are recorded in Table 1.2.

Figure 4: Fast Fourier Transform spectrum of the AM signal

Table 1.1: Spetrum Information (50% Modulation)

Table 1.2 Spectrum Information (100% Modulation)

In conclusion, I used the 3311A function generator and the BK Precision 4040 function generator to produce a simple sine wave, I used both generators to produce an amplitude modulated wave, and used the fast Fourier transform feature to view the spectrum of the signal. This lab helped me become familiar with the lab equipment.