Angle Modulation Transmissions (Chapter 7) Flashcards
Two forms of angle modulation.
FM and PM
Angle modulation was first introduced in the year ________ as
an alternative to amplitude modulation.
1931
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 (θ) of
a sinusoidal wave is varied with respect to time.
Angle Modulation
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 )
Direct FM is Direct Pm. True or False?
False
The relative angular displacement (shift) of the carrier phase
in radians in respect to the reference phase.
Phase Deviation (Δθ )
The relative displacement of the carrier frequency in hertz in
respect to its unmodulated value.
Frequency Deviation (ΔF )
The original unmodulated carrier frequency in the resultant
angle-modulated waveform.
Carrier Rests Frequency
The instantaneous change in the phase of the carrier at a
given instant of time and indicates how much the phase of the carrier is
changing with respect to its reference phase.
Instantaneous Phase Deviation
The precise phase of the carrier at a given instant of time.
Instantaneous Phase
The instantaneous change in frequency of the carrier and is
defined as the first time derivative of the instantaneous phase deviation.
Instantaneous Frequency Deviation
The precise frequency of the carrier at a given instant of
time and is defined as the first time derivative of the instantaneous phase.
Instantaneous 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.
Deviation Sensitivities
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.
Frequency Deviation
The peak-to-peak frequency deviation (2Δf).
Carrier Swing
The ratio of the frequency deviation actually produced to the
maximum frequency deviation allowed by law stated in percent form.
Percent Modulation
A circuit in which the carrier is varied in such a way that
its instantaneous phase is proportional to the modulating signal.
Phase Modulator
A circuit which the carrier is varied in such a way that its
instantaneous phase is proportional to the integral of the modulating signal.
Frequency Modulator
________ of the first kind for several values of modulation
index provides the number of side frequency pairs and their corresponding
magnitude.
Bessel Function
A side frequency is not considered significant unless it has
amplitude equal to or greater than ____ of the unmodulated carrier amplitude.
1%
The modulation index is less than 1.
Low-index Case
The modulation index is greater than 10.
High-index Case
Modulation indices greater than 1 and less than 10.
Medium Index
Low-index FM systems are sometimes called?
Narrowband FM
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.
Carson’s Rule
The worst-case modulation index and is equal to the maximum
peak frequency deviation divided by the maximum modulating-signal frequency.
Deviation Ratio ( DR )
The FCC has assigned the commercial FM broadcast service a
_______ band of frequencies that extends from 88 MHz to 108 MHZ.
20 MHz
The 20–MHz band is divided into 100, ________ wide channels
beginning at 88.1 MHz.
200 kHz
To provide high-quality, reliable music, the maximum frequency
deviation allowed is _______ with a maximum modulating-signal frequency of
_______.
75 kHz ; 15 kHz
The highest side frequencies from one channel are allowed to
spill over into adjacent channels, producing an interference known as
_______.
Adjacent Channel Interference
A _______ wide guard band is usually on either side of each
assigned channel.
200 kHz
The noise voltage at the output of an FM demodulator increases
linearly with frequency. This is called ______.
FM Noise Triangle
The high-frequency modulating signals are emphasized or
boosted in amplitude in the transmitter prior to performing modulation.
Pre-emphasis
The reciprocal of pre-emphasis that restores the original
amplitude-versus-frequency characteristics to the information signals.
De-emphasis
A circuit that provides a constant increase in the amplitude
of the modulating signal with an increase in frequency.
Pre-emphasis Network
When the frequency of the carrier is modulated by the information
signal, _______ results.
Direct FM ( Indirect PM )
When the phase of the carrier is modulated by the information
signal, _______ results.
Direct PM ( Indirect FM )
Angle modulation in which the frequency of the carrier is
varied directly by the modulating signal.
Direct FM
Three common methods for producing direct frequency
modulation.
Varactor Diode, FM Reactance, Linear IC
Modulations
Direct frequency modulator used for low-index Applications,
such as two-way mobile radio.
Varactor Diode Direct FM Modulator
A direct FM modulator using a JFET as the active device.
FM Reactance Modulator
A complete FM modulator on a single 8-pin DIP integrated
circuit chip.
MC1376
Can generate a direct FM output waveform that is relatively
stable, accurate, and directly proportional to the input modulating signal.
Linear IC VCO and Function Generators
Angle modulation in which the frequency of the carrier is
deviated indirectly by the modulating signal.
Direct PM
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.
Frequency Up-Conversion
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.
Heterodyne Method
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.
Multiplication Method
Transmitters that produce an output waveform in which the
frequency deviation is directly proportional to the modulating signal.
Direct FM Transmitters
A circuit that compares the frequency of the 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.
Frequency Discriminator
A voltage added to the modulating signal to automatically
adjust the master oscillator’s center frequency to compensate for the
low-frequency drift.
dc Correction Voltage
A ________ preceded by a differentiator generates a PM
waveform.
FM Modulator
Transmitters that produce an output waveform in which phase
deviation is directly proportional to the modulating signal.
Indirect FM Transmitters
Probably the most significant advantage of angle modulation
transmission over amplitude modulation transmission.
Noise Immunity
Allows a receiver to differentiate between two signals
received with the same frequency.
Capture Effect
Proportional to the amplitude, not the frequency, of the modulating signal.
Frequency Modulation
it is the phase shift, rather than the frequency deviation, that is proportional to the
instantaneous amplitude of the modulating signal.
Phase Modulation
In FM and PM, the frequency deviation is _______ to the amplitude of the modulating signal.
directly proportional
In PM, the maximum leading or lagging phase shift occurs at the _______ of the modulating signal
peak amplitudes
In PM, the carrier deviation is _______ to both the modulating frequency and the amplitude, independent to frequency.
proportional
It is the rate of change of phase (which is the derivative of phase)
Frequency (radians per second)
