Flashcards in Chapter 7 & 8 - Tomasi Deck (50):
Two forms of angle modulation.
FM and PM
Angle modulation was first introduced in the year ________ as an alternative to amplitude modulation.
He developed the first successful FM radio system in 1936, and in July 1939, the first regularly scheduled broad-casting of FM signals began in Alphine, New Jersey. Also developed the superheterodyne receiver.
Major E. H. Armstrong
A modulation that results whenever the phase angle () of a sinusoidal wave is varied with respect to time.
Varying the frequency of a constant-amplitude carrier directly proportional to the amplitude of the modulating signal at a rate equal to the frequency of the modulating signal.
Direct Frequency Modulation
( FM )
Varying the phase of a constant-amplitude carrier directly proportional to the amplitude of the modulating signal at a rate equal to the frequency of the modulating signal.
Direct Phase Modulation
( PM )
The relative angular displacement (shift) of the carrier phase in radians in respect to the reference phase.
The relative displacement of the carrier frequency in hertz in respect to its unmodulated value.
The original unmodulated carrier frequency in the resultant angle-modulated waveform.
Carrier Rests Frequency
Are the output–versus-input transfer functions for the modulators, which give the relationship between what output parameter changes in respect to specified changes in the input signal.
Is called the modulation index or sometimes index of modulation.
Peak Phase Modulation
The change in frequency that occurs in the carrier when it is acted on by a modulating-signal frequency.
The peak-to-peak frequency deviation (2f).
The ratio of the frequency deviation actually produced to the maximum frequency deviation allowed by law stated in percent form.
A rule which is an approximation and gives transmission bandwidths that are slightly narrower than the bandwidths. It defines a bandwidth that includes approximately 98% of the total power in the modulated wave.
The worst-case modulation index and is equal to the maximum peak frequency deviation divided by the maximum modulating-signal frequency.
The FCC has assigned the commercial FM broadcast service a _______ band of frequencies that extends from 88 MHz to 108 MHZ.
The 20–MHz band is divided into 100, ________ wide channels beginning at 88.1 MHz.
To provide high-quality, reliable music, the maximum frequency deviation allowed is _______ with a maximum modulating-signal frequency
75 kHz ;
The high-frequency modulating signals are emphasized or boosted in amplitude in the transmitter prior to performing modulation.
The reciprocal of pre-emphasis that restores the original amplitude-versus-frequency characteristics to the information signals.
When the frequency of the carrier is modulated by the information signal, _______ results.
( Indirect PM )
When the phase of the carrier is modulated by the information signal, _______ results.
( Indirect FM )
Three common methods for producing direct frequency modulation.
Linear IC Modulations
A complete FM modulator on a single 8-pin DIP integrated circuit chip.
Two common methods for producing direct phase modulation.
Varactor Diode and Transistor Direct PM Modulator
The process of up-converting the frequency of the modulated carrier after modulation has been performed.
Two basic methods of performing frequency up-conversion.
Heterodyning and Frequency Multiplication
An up-conversion method where a low-frequency modulated carrier can either be up- or down- converted to a different location in the frequency spectrum without changing its modulation properties.
An up-conversion method where the modulation properties of a carrier can be increased at the same time that the carrier frequency is up-converted.
What does AFC stands for?
Automatic Frequency Control
A circuit that compares the frequency of he non crystal carrier oscillator to a crystal reference oscillator and then produces a correction voltage proportional to the difference between the frequencies.
Automatic Frequency Control
( AFC )
A frequency-selective device whose output voltage is proportional to the difference between the input frequency and its resonant frequency.
Probably the most significant advantage of angle modulation transmission over amplitude modulation transmission.
Allows a receiver to differentiate between two signals received with the same frequency.
A method used to remove amplitude variations caused by noise from the composite waveform simply by clipping the peaks of the envelop prior to detection.
The section that establishes the signal-to-noise ratio and noise figure in FM receivers.
The envelope (peak) detector common to AM receivers is replaced in FM receivers by a ________, ________, and ________.
Frequency Discriminator and
The circuit that extracts the information from the modulated wave.
This FM demodulator requires no tuned circuits and automatically compensates for changes in the carrier frequency due to instability in the transmit oscillator.
PLL FM Demodulator
The limiter circuit produces a constant-amplitude output for all input signals above a prescribed minimum input level, which is often
called the ________.
The improvement in the S/N ratio when the peaks of the signal have the limiter so far into saturation that the weaker noise is totally eliminated.
FM Thresholding, FM Quieting, or
FM Capture Effect
The inherent ability of FM to diminish the effects of interfering signals. Also, the ability to differentiate between two signals received at the same frequency.
A circuit that is used to reduce the total harmonic distortion (THD) by compressing the IF frequency swing (deviation).
The amount an FM carrier frequency deviates for a given modulating input voltage level is called the ________.
Are used to multiply the frequency of the carrier signal of an FM signal, consist of a class C amplifier followed by a tank circuit that filters out a single harmonic, and are used to multiply the frequency deviation of an FM signal
Another way to describe the modulation index is using the _________.
The input signal into a PLL is at the ________.
FM with less than or equal to 0.3 of modulation index is referred to as ______.
Narrow Band FM