Chapter 5: Fundamentals of Frequency Modulation Flashcards
A ______________ carrier can be modified for the purpose of transmitting information from one place to another by varying its frequency. This is known as frequency modulation (FM).
Sine wave
In _____, the carrier amplitude remains constant and the carrier frequency is changed by the modulating signal.
FM
As the amplitude of the information signal varies, the carrier frequency shifts _____________________.
Proportionately
As the modulating signal amplitude increases, the carrier frequency __________________.
Increases
With no modulation the carrier is at its normal center or _____________.
Resting frequency
___________________ is the amount of change in carrier frequency produced by the modulating signal.
Frequency deviation
The _______________________ is how many times per second the carrier frequency deviates above or below its center frequency.
Frequency deviation rate
The ________________of the modulating signal determines the frequency deviation rate.
Frequency
A type of modulation called ____________________________ is used in transmission of binary data in digital cell phones and low-speed computer modems.
Frequency-shift keying (FSK)
When the amount of phase shift of a constant- frequency carrier is varied in accordance with a modulating signal, the resulting output is a _________________________ signal.
Phase- modulation (PM)
_____________________ produce a phase shift which is a time separation between two sine waves of the same frequency.
Phase modulators
The greater the ___________________of the modulating signal, the greater the phase shift.
Amplitude
The _________________________produced by a phase modulator occurs during the time that the modulating signal is changing at its most rapid rate.
Maximum frequency deviation
In FM and in PM, the frequency deviation is _________________ to the amplitude of the modulating signal.
Directly proportional
In _________, the maximum amount of leading or lagging phase shift occurs at the peak amplitudes of the modulating signal.
PM
In PM the ______________ is proportional to both the modulating frequency and the amplitude.
Carrier deviation
In order to make PM compatible with FM, the deviation produced by frequency variations in the modulating signal must be _________.
Compensated
This compensation can be accomplished by ______the intelligence signal through a low-pass RC network.
Passing
This RC low-pass filter is called a frequency- correcting network, predistorter, or 1/f filter and causes the higher modulating frequencies to be ___________.
Attenuated
The FM produced by a phase modulator is called ____________.
Indirect FM
The process of phase modulating a carrier with binary data is called _____________________ or ___________________________.
Phase-shift keying (PSK), Binary phase-shift keying (BPSK).
The PSK signal has a ______________________, but the phase of the signal from some reference changes as the binary modulating signal occurs.
Constant frequency
Any modulation process produces ____________. When a constant-frequency sine wave modulates a carrier, two side frequencies are produced.
Sidebands
Side frequencies are the sum and difference of the carrier and ___________________.
Modulating frequency
The bandwidth of an FM signal is usually much _______ than that of an AM signal with the same modulating signal.
Wider
The ratio of the frequency deviation to the modulating frequency is known as the __________________.
Modulation index (m)
In most communication systems using FM, maximum limits are put on both the _______________ and the __________.
Frequency deviation, modulating frequency.
In standard FM broadcasting, the maximum permitted frequency deviation is ________ and the maximum permitted modulating frequency is 15 kHz.
75 kHz
The modulation index for standard FM broadcasting is therefore __.
5
The equation that expresses the phase angle in terms of the sine wave modulating signal is solved with a complex mathematical process known as _______________.
Bessel functions
The higher the modulation index in FM, the ______ the number of significant sidebands and the wider the bandwidth of the signal.
Greater
When ________ conservation is necessary, the bandwidth of an FM signal can be restricted by putting an upper limit on the modulation index.
Spectrum
______ is interference generated by lightning, motors, automotive ignition systems, and power line switching that produces transient signals.
Noise
Noise is typically narrow ______ of voltage with high frequencies.
spikes
Noise (voltage spikes) add to a signal and ______ with it.
interfere
Some noise completely _______________ signal information.
obliterates
FM signals have a __________ modulated carrier amplitude.
constant
FM receivers contain limiter circuits that deliberately restrict the ____________ of the received signal.
amplitude
Any _______________ variations occurring on the FM signal are effectively clipped by limiter circuits.
amplitude
This amplitude clipping does not affect the information content of the FM signal, since it is contained solely within the frequency variations of the _____________.
carrier
Noise can interfere with an ___ signal and particularly with the high-frequency components of the modulating signal.
FM
Noise is primarily sharp spikes of energy and contains a lot of _________ and other high-frequency components.
harmonics
A simple high-pass filter can serve as a transmitter’s ________________ circuit.
pre-emphasis
To overcome high-frequency noise, a technique known as _____________ is used.
pre-emphasis
Pre-emphasis provides more _____________ of only high- frequency components.
amplification
A simple low-pass filter can operate as a __________________ circuit in a receiver.
deemphasis
A de-emphasis circuit returns the frequency response to its normal ___________ level.
flat
The combined effect of preemphasis and deemphasis is to increase the signal-to-noise ratio for the high-
frequency components during transmission so that they will be _________________ and not masked by noise.
stronger
FM has superior immunity to __________, made possible by clipper limiter circuits in the receiver.
noise
In FM, interfering signals on the same frequency are rejected. This is known as the ______________.
capture effect
FM signals have a constant amplitude and there is no need to use linear amplifiers to increase power levels. This increases ________________.
transmitter efficiency
In the past, the circuits used for frequency modulation and demodulation involved were complex. With the __________________of ICs, complex circuitry used in FM has all but disappeared. ICs are inexpensive and easy to use. FM and PM have become the most widely used modulation method in electronic communication today.
proliferation
FM uses considerably more frequency _______________ space.
spectrum
FM has used more complex circuitry for ______________________ and _______________________.
modulation , demodulation
