- Preemphasis improvement
In FM broadcasting, preemphasis improvement is the improvement in the
signal-to-noise ratio of the high-frequency portion of thebaseband , "i.e.," modulating, signal, which improvement results from passing the modulating signal through apreemphasis network .Preemphasis increases the magnitude of the higher signal frequencies, thereby improving the signal-to-noise ratio. At the
output of thediscriminator in the FM receiver, adeemphasis network restores the original signal power distribution."FM improvement factor" is the quotient obtained by dividing the
signal-to-noise ratio (SNR) at theoutput of an FM receiver by thecarrier-to-noise ratio (CNR) at theinput 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 thethermal noise generated in the receiver. Abaseband signal-to-noise ratio of about 30 dB is typical at the improvementthreshold , and this ratio improves 1 dB for each decibel of increase in the signal above the threshold.ource
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Federal Standard 1037C
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