Preemphasis improvement
Encyclopedia
In FM broadcasting, preemphasis improvement is the improvement in the signal-to-noise ratio
of the high-frequency
portion of the baseband
, i.e., modulating, signal, which improvement results from passing the modulating signal through a preemphasis network
.
Preemphasis increases the magnitude of the higher signal frequencies, thereby improving the signal-to-noise ratio. At the output
of the discriminator
in the FM receiver, a deemphasis
network restores the original signal power
distribution.
FM improvement factor is the quotient obtained by dividing the signal-to-noise ratio
(SNR) at the output
of an FM
receiver by the carrier-to-noise ratio
(CNR) at the input of the receiver. When the FM improvement factor is greater than unity, the improvement in the SNR is always obtained at the expense of an increased bandwidth in the receiver and the transmission
path.
FM improvement threshold is the point in an FM (frequency modulation
) receiver at which the peaks in the RF signal equal the peaks of the thermal noise generated in the receiver. A baseband
signal-to-noise ratio
of about 30 dB
is typical at the improvement threshold, and this ratio improves 1 dB for each decibel of increase in the signal above the threshold.
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
of the high-frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
portion of the baseband
Baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
, i.e., modulating, signal, which improvement results from passing the modulating signal through a preemphasis network
Preemphasis network
In telecommunication, a pre-emphasis network is a network inserted in a system in order to increase the magnitude of one range of frequencies with respect to another....
.
Preemphasis increases the magnitude of the higher signal frequencies, thereby improving the signal-to-noise ratio. At the output
Output
Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...
of the discriminator
Discriminator
Discriminator is a typed tag field present in OMG IDL discriminated union type and value definitions that determines which union member is selected in the current union instance. Unlike in some conventional programming languages offering support for unions, discriminator in IDL is not identical to...
in the FM receiver, a deemphasis
Deemphasis
In telecommunication, de-emphasis is the complement of pre-emphasis, in the antinoise system called emphasis. Emphasis is a system process designed to decrease, , the magnitude of some frequencies with respect to the magnitude of other frequencies in order to improve the overall signal-to-noise...
network restores the original signal power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
distribution.
FM improvement factor is the quotient obtained by dividing the signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
(SNR) at the output
Output
Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...
of an FM
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
receiver by the carrier-to-noise ratio
Carrier-to-noise ratio
In telecommunications, the carrier-to-noise ratio, often written CNR or C/N, is the signal-to-noise ratio of a modulated signal. The term is used to distinguish the CNR of the radio frequency passband signal from the SNR of an analogue base band message signal after demodulation, for example an...
(CNR) at the input of the receiver. When the FM improvement factor is greater than unity, the improvement in the SNR is always obtained at the expense of an increased bandwidth in the receiver and the transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
path.
FM improvement threshold is the point in an FM (frequency modulation
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
) receiver at which the peaks in the RF signal equal the peaks of the thermal noise generated in the receiver. A baseband
Baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
of about 30 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
is typical at the improvement threshold, and this ratio improves 1 dB for each decibel of increase in the signal above the threshold.