Expt(mixer)

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Mixer Experiment No. 3 In Communication Theory

Submitted By: BSECE – 2A

Submitted to: Engr. Edbert Aquitania

Date Performed: 15 August 2009 Date Submitted: 22 August 2009

I. OBJECTIVES 1. To observe the difference frequency out of a mixer. 2. To obtain the approximate cutoff frequency.

II. MATERIALS AND EQUIPMENTS +/- 15 Vdc Power Supply Oscilloscope Function Generator Alligator clips Connecting wires Breadboard

III. WIRING DIAGRAM

IV. PROCEDURE 1. If fx = in Fig. 3-1, what does the difference frequency equal? Record your answer. 2. The mixer output of fig 3-1 is filtered by two low-pass RC circuits. The approximate cutoff frequency of each is given by fc = 1/ 2ΠRC. Calculate fc. 3. Connect the circuit of fig. 3-1 4. Turn Vy down to 0. With the oscilloscope, adjust Vx to 0.1 Vp-p. Set the frequency to. 5. Next, adjust Vy to 1 Vp-p and 6. Look at the final output signal with a vertical sensitivity of 0.1V/cm. (AC input) and a sweep time of 0.2ms/cm. Vary the frequency of the Vx generator slowly in the vicinity of until you get a output signal. 7. Look at point B, the input to the final RC filter. Note thr ripple on the signal. 8. Look at point A, the input to the first RC filter. Use a vertical sensitivity of 2V/cm. Note how large the ripple is here.

VI. DATA AND RESULT

Input x

Input y

Output

Output at point A

Output at point B

Ripple at point A

VII. COMPUTATIONS: Bx = 250KHz By = 25KHz Input: @ By: Fy = 25 KHz Vy = 0.9 Vp-p @ Bx: Fx = 250KHz Vy = 10Vp-p @ point A Vripple = 1.2Vp-p @ point B Vripple = 0.13Vp-p Vout = 1.2 *5mV =6mV Fout = 25 KHz

VIII. TEST YOUR KNOWLEDGE

Ripple at point B

1.

Why do you see the original frequencies (and) at the output?

2.

In fig. 3-1, what contains the output signal? (Considering and input

3. What is the other name for the mixing process? 4. Does mixing the same as AM? 5.

Is the main purpose of a mixer?

IX. DISCUSSION X. CONCLUSION

frequencies)