This is the Coaching materials in Noise Part 1 as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Noise Coaching Materials Part 1
1. “Man-made” noise can come from:
Ans. equipment that sparks *
2. Thermal noise is generated in:
Ans. transistors and diodes, copper wire, and resistors *
3. Shot noise is generated in:
Ans. transistors and diodes *
4. The power density of “flicker” noise is:
Ans. greater at low frequencies *
5. So called “1/f” noise is also called:
Ans. pink noise *
6. “Pink” noise has:
Ans. equal power per octave *
7. Noise figure is a measure of:
Ans. how much noise an amplifier adds to a signal *
8. Resistor that generates the lowest thermal noise:
Ans. wire-wound *
9. Resistor with typical voltage range of
Ans. metal film*
10. Reference for noise temperature in ˚C:
Ans. 17 *
11. Standard test tone connected on audio equipment?
Ans. 1.0 kHz tone *
12. Reference standard test tone normally used is indicated in:
Ans. dBm *
13. Power lost in device, due by the path of energy flow.
Ans. insertion loss *
14. The noise generated with semiconductor devices.
Ans. shot noise *
15. Bandwidth is approximately _____ the highest baseband frequency.
Ans. 2 times *
16. Flicker noise in radio communications is also known as.
Ans. pink noise *
17. What determines the BW of a transmitted signal?
Ans. the highest frequency component of modulating signal *
18. What formula is used to calculate the overall noise performance of the receiver or of multiple stages if RF amplification?
Ans. Frii’s formula *
19. If the bandwidth is doubled, considering all other parameters unchanged except the normal thermal noise only. The S/N will be___
Ans. decreased by 3 dB *
20. Noise at the receiver is in terms of:
Ans. µV *
21. Reference tone level for µBa:
Ans. – 85 dBm *
22. Reference tone level for dBrn:
Ans. -90 dBm *
23. Reference tone level for F1A:
Ans. -85 dBm *
24. Reliable measurement for comparing amplifier noise characteristics:
Ans. noise factor *
NOISE PROBLEMS
25. A receiver has noise power bandwidth of 10 kHz. A resistor that matches the receiver input impedance is connected across its antenna terminals. What is the noise power contributed by that resistor in the receiver bandwidth if the resistor has a temperature of 27 degrees Celsius?
Ans. 4.14 x 10-27 W
26. A 300 ohm resistor is connected across the 300 ohm antenna input of the television receiver. The bandwidth of the receiver is 6 MHz, and the resistor is at room temperature. Find the noise power and noise voltage applied to the receiver input.
Ans. 24.2 fW, 2.7 uV.
27. A diode noise generator is required to produce a 10 uV of noise in a receiver with an input impedance of 75 ohms, resistive, and a noise power bandwidth of 200 kHz. What must be the current through the diode be?
Ans. 276 mA
28. Two noise-source resistors R1 and R2 connected in series at different temperatures, 300˚K and 400˚K respectively. If R1 = 100 Ω, R2 = 200, find:
A. the total noise voltage
B. the noise power at the load with RL = 300Ω, over a BW = 100 kHz.
Ans. A. 779 nV; B. 0.506 fW
29. A receiver produces a noise power of 200mW with no signal. The output level increases to 5W when a signal is applied. Calculate (S+N)/N as a power ratio and in decibels.
Ans. 25, 14 dB
30. The signal power at the input to an amplifier is 100 uW and the noise power is 1 uW. At the output, the signal power is 1W and the noise power is 30 mW. What is the amplifier noise figure, as a ratio? In dB?
Ans. 3; 4.77 dB
31. The signal at the input of an amplifier has an S/N of 42 dB. If the amplifier has a noise figure of 6 dB, what is the S/N at the output in decibels?
Ans. 36 dB
32. An amplifier has a noise figure of 2 dB. What is the equivalent noise temperature?
Ans. 170 K
33. A three-stage has stages with the following specifications: First stage with power gain and noise figure of 10 and 2 respectively, 25 and 4 for the second stage and 30 and 5 for the third stage. Find the noise temperature.
Ans. 382 K
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