This is the Review Notes 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
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