Group Study - Db Noise Answer Key

GROUP STUDY - dB Noise 1. Indicate the voltage level in dB with reference to one volt. This unit is used in video or TV measurement. a. dBW

b. dBk

c. dBm

d. dBV

2. When the power ratio of the output to input of a circuit is 200. What is the gain in dB? a. 23

b. 46

c. – 23

d. – 46

3. What is the reference level for random noise measurement, FIA weighted? a. – 82 dBm

b. – 90 dBm

c. – 85 dBm

d. – 77 dBm

4. A 10 db pad has an output level of -3dBm. The level at the input is: a. 13 dBm

b. – 7 dBm

c. 1 dBm

d. 7 dBm

5. A power level of 50 μW could be expressed as: a. 1.69 dBm

b. – 4.3 dBm

c. 1 dBm

d. – 13 dBm

6. A system having an input power of 2 mW an output power of 0.8 mW has a loss of: a. 2.98 dBm

b. 3.98 dB

c. 3.98 μW

d. 1.98 mW

7. Is the reduction of signal amplitude as it passed over the transmission medium? a. Noise

b. Distortion

c. Attenuation

d. Interface

8. Signal waveform perturbation or deviation caused by imperfect response of the system to the desired signal a. Noise

b. Aliasing

c. Distortion

d. Interference

9. Signal attenuation can be corrected by a. Filtering

b. Modulation

c. Equalization

d.

Amplification 10.

Signal contamination by extraneous or external sources, such as, other

transmitters, power lines and machinery. a. Noise 11.

b. Distortion

d. Interference

Which noise figure represents the lowest noise?

a. 1.5 dB 12.

c. Harmonics

b. 2.0 dB

c. 3.7 dB

d. 4.1 dB

Denote the interference of noise in dB above an adjusted reference noise. The

adjusted reference noise level was a 1 kHz tone, set at – 85 dBm a. dBa 13. a. S/N 14. a. 0 dB

b. dBm

c. dBa0

d. pWp

A more precise evaluation of the quality of a receiver as far as noise is concerned. b. VSWR

c. Noise factor

d. Noise margin

Noise figure for an amplifier with noise is always b. Infinite

c. Less than 1

d. Greater than 1

15.

A passive circuit, usually consisting of capacitance and/or inductance, that is

inserted in series with the a-c power cord of an electronic device which allow the 60-Hz current to pass and suppressed high frequency noise components. a. Noise filter

b. Noise limiter

c. Noise floor

d. Noise

quieting 16.

A circuit often used in radio receivers that prevents externally generated noise from

exceeding certain amplitude. They are also called noise clippers. a. Noise floor 17.

b. Noise filter

c. Noise limiter

d. Noise clamper

Extra-terrestrial noise is observable at frequencies from

a. 0 to 20 KHz 18.

b. 8 Mhz to 1.43 GHz

c. 5 to 8 GHz

d. 15 to 60 MHz

An amplifier operating over the frequency range of 455 to 460 kHz has a 200 kΩ

input resistor. What is the RMS noise voltage at the input to this amplifier if the ambient temperature is 17°C? a. 40 μV 19.

b. 4.0 μV

c. 400 μV

d. 4.0 mV

Calculate the noise figure of the amplifier whose Req equals 2518 Ω (R T = 600 Ω) if

it’s driven by a generator whose output impedance is 50Ω a. 39.4 20.

b. 3.94

c. 394

d. 0.394

A receiver connected to an antenna whose resistance is 50 Ω has an equivalent

noise resistance of 30 Ω. Calculate its equivalent noise temperature if the noise figure is equal to 1.6 a. 17.4 K 21.

b. 174 K

c. 1.74 K

d. 17 K

Which of the following is not a source of external noise?

a. Thermal agitation

b. Auto ignition

c. The sun

d. Fluorescent

lights 22.

What is the noise voltage across a 300 Ω input resistance to a TV set with a 6 MHz

bandwidth and temperature of 30°C? a. 2.3 μV 23.

b. 3.8 μV

d. 6.4 μV

If bandwidth is doubled, the signal power is _____

a. Not changed 24.

c. 5.5 μV

b. Quadrupled

c. Tripled

d. Doubled

A network that has an input of 75 dB and an output of 35dB. The loss of the network

is _____ a. -40 dB 25.

b. 40 dB

c. -40 dBm

d. 40 dBm

If an amplifier has equal input and output impedances, what voltage ratio does the

gain of 50 dB represent? a. 316.2

b. 325.2

c. 320.1

26. Generally referred to as the primary cause of atmospheric noise a. El Nino phenomenon b. lightningc. rain effect d. thunderstorm 27. Extra terrestrial noise is observable at frequencies from

d. 315.0

a. 5 to 8 GHz 28.

B. 0 to 20 kHz

c. 1 to 1.43 GHz

d. above 2

GHz Noise that is non-continuous, consisting of irregular pulses or noise spikes of short

duration with high amplitudes. a. Shot b. transit time c. impulse d. flicker 29. A receiver connected to an antenna whose resistance is 50 ohms has an equivalent noise resistance of 30 ohms. What is the receiver’s noise temperature? a. 754 deg K b. 464 deg K c. 174 deg K d. 293 deg K 30. The noise figure of a totally noiseless device is a. Unity b. infinity c. zero d. cannot be determined 31. Industrial noise frequency is between a. 200 and 3000 MHz b. 15 to 160 MHz c. 0 to 10 kHz d. 20 GHz 32. An amplifier operating over a 15 kHz bandwidth has a 500 kohm input resistor. What is the rms noise voltage at the input to this amplifier if the ambient temperature is 23 deg C? a. 11 uV b. 110 uV c. 0.11 uV d. 1.1 uV 33. It is the interference of a signal from one channel to another channel. a. Intermodulation distortion b. sideband splatter c. spur d. crosstalk 34. A signal is amplified 100 times in power. The dB gain is a. 10 dB b. 20 dB c. 30 dB d. 40 dB 35. The random and unpredictable electric signals from natural causes, both internal and external to the system is known as a. Distortion b. noise c. attenuation d. interference 36. What is the noise power at room temperature when the bandwidth is 1kHz? a. 4 x 10exp-18 w b. 2 x 10exp -19 w c. 3.45 x 10exp -19 w d. 3.45 x 10exp18w 37. Unit of noise power of psophometer a. dBa b. pWp c. dBm d. dBm0 38. 25dBrnC F1A weighted equals to a. -60 dBm b. -63 dBm c. -65 dBm d. -67 dBm 39. If you have available number of power amplifiers with a gain of 100 each, how many such amplifiers do you need to cascade to give an overall gain of 60dB? a. 2 b. 3 c. 4 d. 5 40. Which noise figure represents the lowest noice? a. 1.6 dB b. 2.1 dB c. 2.7 dB d. 3.4 dB 41. It is also known as burst noise. a. Johnson b. Popcorn c. Shot d. Mixer 42. What type of noise dominates at lower frequencies? a. Pink b. Transit Time c. Shot d. Thermal Agitation 43. Two resistors, 5kohms and 20 kohms are at 27degC. Calculate the thermal noise voltage of the series combination for a 10kHz bandwidth. a. 4.01 uV b. 5 uV c. 2.03 uV d. 3.02 uV 44. Determine the noise current for a diode with a forward bias of 3.5 mA over a 100 kHz bandwidth. a. 10.58 nA b. 0.335 nA c. 21.2 nA d. 5.6 nA 45. Another name for Johnson Noise a. Flicker b. White c. IMD d. Shot 46. What is the difference between – 18 and 22 dBm? a. 40 dB b. 40 dBm c. 4 dB d. 4 dBm 47. A combiner has 2 inputs of +40dBm, what is the resultant output?

a. 46 dBm b. 40 dBm c. 80 dBm d. 43 dBm 48. Noise that is very intense and it comes from sources which are points in the sky. a. Flicker b. Industrial c. Thermal Agitation d. Galactic 49. The input power to a loss free cable is 5w. If the reflected power is 7dB down on the incident power, the output power to the load is a. 4w b. 5w c. 6 w d. 7w 50. How many watts are represented by 40dBw? a. 40000w b. 1000w c. 40 w d. 10000w 51.

One of the following types of noise becomes of great importance at high

frequencies. It is the a. shot noise 52.

b. random noise

c. impulse noise

d. transit-time noise

Indicate the false statement.

a. HF mixers are generally noisier than HF amplifiers. b. Impulse noise voltage is independent of bandwidth. c. Thermal noise is independent of the frequency at which it is measured. d. Industrial noise is usually of the impulse type. 53.

The value of a resistor creating thermal noise is doubleThe noise power generator

is therefore a. halved 54.

b. quadrupled

c. doubled

d. unchanged

One of the following is not a useful quantity for comparing the noise performance

of receivers: a. Input noise voltage

b. Equivalent noise resistance

c. Noise temperature

d. Noise figure

55.

Indicate the noise whose source is in a category different from that of the other

three. a. Solar noise

b. Cosmic noise

c. Atmospheric noise

d. Galactic

noise 56.

Indicate the false statement. The square of the thermal noise voltage generated by

a resistor is proportional to a. its resistance

b. its temperature

c. Boltzmann’s constant

d. the bandwidth over which it is measured

57.

Which of broad classifications of noise are most difficult to treat?

a. noise generated in the receiver c. externally generated noise 58.

b. noise generated in the transmitter d. internally generated noise

Space noise generally covers a wide frequency spectrum, but the strongest

interference occurs a. between 8 MHz and 1.43 GHz

b. below 20 Mhz

c. between 20 to 120 MHz

d. above 1.5 GHz

59.

When dealing with random noise calculations it must be remembered that

a. all calculations are based on peak to peak values b. calculations are based on peak values c. calculations are based on average values d. calculations are based on RMS values 60.

Which of the following is the most reliable measurement for comparing amplifier

noise characteristics? a. signal-to-noise ratio 61.

b. noise factor

c. shot noise

d. thermal noise agitation

Which of the following statements is true?

a. Random noise power is inversely proportional to bandwidth b. Flicker is sometimes called demodulation noise c. Noise is mixers is caused by inadequate image frequency rejection d. A random voltage across a resistance cannot be calculated 62.

Voltage gain in decibels is

a. 10 ln (V2/V1) 63.

c. 20 ln (V2/V1)

d. 20 log (V2/V1)

Which expression indicates a measurement using a 1-W reference

a. dBm(1)

64.

b. 10 log (V2/V1) b. dB1

c. dBW

d. dB(W)

An amplifier operating over a 2-Mhz bandwidth has a 75Ω input resistance. If it is

operating at 22° C and has a voltage gain of 300, the noise produced at the output of this amplifier would be approximately a. 128 μV 65.

c. 1.56 μV

d. 468 μV

Which of the following is not an example of external noise

a. Fluorescent light 66.

b. 7.33 pV

b. Solar emission

c. Resistor noise d. Lightning

A current change that is equal to twice its original value will correspond to a change

of a. 3 dB 67.

b. 9 dB

c. 10 dB

d. 6 dB

What does a power difference of -3 dB mean?

a. a loss of one third of the power

c. a loss of one-half of the power

b. a loss of 3 watts of power

d. no significant change

68.

A gain of 60 dB is the same as a gain of

a. 10 volts/volt 69.

b. 100 volts/volt

c. 1000 volts/voltd. 10,000 volts/volt

_____ is mathematically equal to the logarithm to the base ten of the power ratio P1

over P2. a. Bel 70.

b. dB

c. bel/10

d. dB/2

Noise that is produced by the active components within the receiver.

a. Thermal

b. external

c. internal

d. white

71.

Noise due to the random variation in the arrival of charge carriers at the output

electrode of an active device. a. Shot 72.

c. thermal

d. dynamic

A network has a loss of 20 dB. What power ratio corresponds to this loss?

a. 0.01 73.

b. impulse b. 0.1

c. 10

d. 100

A receiver connected to an antenna whose resistance is 60 ohms has an equivalent

noise resistance of 40 ohms. Calculate the receiver’s noise figure in decibels and its equivalent noise temperature. a. 1.67 & 194K 74.

b. 2.23 & 194 K c. 1.67 & 174K

d. 2.23 & 174K

_____ Noise is the most prevalent noise found in urban areas and is normally caused

by the arc discharge from automobile or aircraft ignition systems, induction motors, switching gears, high voltage lines and the like. a. Industrial 75.

c. Flicker

d. Mixer

The noise figure of a totally noiseless device is

a. Unity 76.

b. Johnson b. infinity

c. zero

d. 100

Indicate the noise whose source is in a category different from that of the other

three. a. Solar 77.

b. cosmic

c. atmospheric

d. galactic

It is characterized by high amplitude peaks of short duration in the total noise

spectrum. a. intermodulation voice b. impulse noise c. dropout 78.

d. phase hits

A network has a power gain of –3dB. If the input power is 100 watts, the output

power is a. 50 watts 79.

b. 55 watts

c. 60 watts

d. 62 watts

Which of the following types of noise becomes of great importance at high

frequencies? a. shot 80.

b. random

c. impulse

d. transit time

The input current of a network is 190 A and the output is 1.3 A. The loss in

decibels is a. 20.2 81.

b. 21.6

c. 28.6

d. 43.3

If 4 networks connected in series have gains of –0.5 dB, -0.3 dB, -2 dB and 6.8 dB,

the overall gain is a. 2 dB 82. a. 20 83.

b. –2 dB

c. 4 dB

d. –4dB

What is the gain, in dB, if the output to input ratio is 1000. b. 30

c. 40

d. 10

The following are characteristics of noise except

a. unwanted energy

c. predictable in character

b. present in the channel 84.

The equivalent noise temperature of the amplifier is 25K, what is the noise figure?

a. 10.86 85.

d. due to any cause

b. 1.086

c. 0.1086

d. 1.86

A receiver connected to an antenna whose resistance is 50 ohms has an equivalent

noise resistance of 30 ohms. What is the receiver’s noise temperature? a. 464K 86.

d. 174 K

b. 0.1151

c. 6.868

d. 0.5111

What is the equivalent output of a circuit in dBm, if it has an output of 10 watts?

a. 10 dBm 88.

c. 400 K

A theoretical antenna has a gain of 1 dB. Its gain in nepers is

a. 8.686 87.

b. 754 K

b. 30 dBm

c. 20 dBm

d. 40 dBm

An amplifier with an input resistance of 1000 ohms is operating over a 4 MHz

bandwidth. Calculate the rms noise voltage if the amplifier is operating at 27 C. a. 8.14 nV 89.

b. 8.14 V

c. 6.6 nV

d. 6.6 V

The value of a resistor creating thermal noise is doubled. The noise power

generated is therefore a. Halved 90.

c. doubled

d. unchanged

A system having an input power of 2 mW an output power of 0.8 mW has a loss of:

a. 2.98 dBm 91.

b. quadrupled b. 3.98 dB

c. 3.98 W

d. 1.98 mW

Any unwanted form of energy that tends to interfere with the wanted signals is

called a. Noise 92.

b. dB

d. db

b. External

c. Shot

d. Industrial

b. Industrial

c. Extraterrestial

d. Galactic

A 10 db pad has an output level of –3 dBm. The level at the input is:

a. 13 dBm 96.

c. Db

_____ is the noise created by man.

a. Solar 95.

d. absorption

_____ is the noise created outside the receiver.

a. Internal 94.

c. radiation

The correct symbol for decibel is

a. DB 93.

b. spectrum

b. –7 dBm

c. 1 dBm

d. 7 dBm

Indicate the voltage level in dB with reference to one volt. This unit is used in video

or TV measurement. a. dBW 97.

c. dBm

d. dBV

Which of the following is not an actual amount of power?

a. dB 98.

b. dBk b. dBm

c. dBw

d. dBk

In noise analysis, the reference temperature is

a. 75 K

b. 250 K

c. 290 K

d. 300 K

99.

Noise from distant planets, stars, galaxies and other celestial objects are called

a. Cosmic 100.

b. extraterrestrial

c. galactic

d. black body

Indicate which one of the following types of noise does not occur in transistors:

a. shot noise

b. flicker noise

c. partition noise d. resistance noise