Reviewer in Noise | ECE Board Exam

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(Last Updated On: February 15, 2020)

Review Notes in Noise

This is the Reviewer in Noise 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.

Summary of Important Noise Review Notes

Jitter is a non-continuous noise of irregular pulses or spikes of short duration with high amplitudes

Shannon-Hartley theorem sets a limit on the maximum capacity of a channel with a given noise level

Quantizing noise occurs in PCM

Noise always affects the signal in a communications system at the channel

Noise is the random and unpredictable electric signals from natural causes, both internal and external to the system

Gaussian noise/White noise/Thermal noise – Noise from random acoustic or electric noise that has equal energy per cycle over a specified total frequency band

The approximation of the quantized signal causes a quantization noise in PCM system

Limiter – a particular circuit that rids FM of noise

290 K is the reference noise temperature

Noise – unwanted radio signal on assigned frequency

Noise factor is the reliable measurement for comparing amplifier noise characteristics

White noise is measured on a circuit when it is correctly terminated but does not have any traffic

CCITT G. 151 standard recommends crosstalk limits

CCITT Rec. G. 172 standard is utilized in the intermodulation noise rates on PCM audio channels

800 Hz is the reference frequency of CCITT phosphometric noise measurement

290 K – reference temperature used in noise analysis

Atmospheric noise is produced by lightning discharge in thunderstorms

Man-made noise is usually from transmission over power lines and by ground wave

Nif stands for Noise improvement factor

Industrial noise frequency is between 15 to 160 MHz

External noise fields are measured in terms of peak values

Precipitation static – form of interference caused by rain or dust storms

Thermal noise is an electric noise produced by thermal agitation of electrons in conductor and semiconductor

Crosstalk is the interference coming from other communications channels

-90 dBm is the reference noise level

pWp is the unit of noise power of psophometer

Solar flare – a large emission of hydrogen from the sun that affects communications

Atmospheric noise is known as static noise

290 K – standard design reference for environmental noise temperature

C + 273 – absolute temperature in Kelvin

If bandwidth is doubled, the signal power is not changed

Galaxies and internal combustion engines are sources of noise bearing on electronic communications

De-emphasis in the receiver in effect attenuates modulating signal components and noise in high frequency range

Atmospheric noise or static is not a great problem at frequencies above 30 MHz

Is the proper procedure for suppressing electrical noise in a mobile station is to apply shielding and filtering where necessary

The noise generated that primarily determines the signal-to-noise ratio in a VHF (150 MHz) marine-band receiver is in the receiver front end

The difference between signal strength at a given point and a reference level is level

Interfering effect of noise, C message weighted, is dBrnc

F1A weighting refers to F1A handset

Power is definite amount of energy per time period

Reference noise is a noise that creates the same interfering effect as a 1000 Hz, -90 dBm tone, a noise than creates zero dBrn in a voice channel

A practical dBrn measurement will almost always in a positive number

-85 dBm is the reference level for noise measurement, F1A weighted

-90 dBm is the reference tone level for dBm

-85 dBm is the reference tone level for dBa

Atmospheric noise becomes less severe at frequencies above 30 MHz

The value of the resistor creating thermal noise is doubled. The noise power generated is therefore unchanged

Input noise voltage is not a useful quantity for comparing the noise performance of receivers

Most internal noise comes from thermal agitation

Thermal agitation is not a source of external noise

Noise can be reduced by narrowing the bandwidth

Noise at the input to a receiver can be as high as several microvolts

Mixer circuit contributes most of the noise in a receiver

The transistor with the lowest noise figure in the microwave region is a MESFET

Transmit-time noise becomes of great importance at high frequencies

The solar cycle repeats the period of great electrical disturbance approximately every 11 years

The square of the thermal noise voltage generated by a resistor is proportional to its resistance, its temperature and the bandwidth over which it is measured

Quantizing noise – noise occurring in the presence of signal resulting from a mismatch between the exact value of an analog signal and the closest available quantizing step in a digital coder

Impulse noise – Noise consisting of irregular pulses of short duration and relatively high amplitude

Crosstalk – noise the occurs via capacitive or inductive coupling in a cable

Sources of impulse noise induced in communication channels: Erroneous digital coding bit caused by an error on a transmission facility, transients due to relay operation and crosstalk from dc signaling systems

Crosstalk due to incomplete suppression of sidebands or to intermodulation of two or more frequency-multiplexed channels which are unintelligible is classified as miscellaneous noise

Psophometer is a device that measures the internal open circuit voltage of an equivalent noise generator having an impedance of 600 ohm and delivering noise power to a 600 ohm load

Cosmic noise – external noise originating outside the solar system

Solar noise – a noise whose source is within the solar system

Noise density – the total noise power present in a 1-Hz bandwidth

Lightning is the primary cause of atmospheric noise

Space noise – noise coming from the sun and stars

The major cause of atmospheric or static noise is thunderstorms

MESFET is a low noise transistor commonly used at microwave frequencies

Complete List of Communications Engineering Review Notes

Complete List of Communications Engineering Review Notes

Important List of Communications Engineering Materials

Share your Notes in Noise

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