Modulation & Demodulation (rev.01)

This is a quiz created by Sid for review of Mod/DeMod – rev.01 by QLM

Modulation

The process of varying a carrier signal in order to transmit information, typically by altering its amplitude, frequency, or phase.

Demodulation

The process of extracting the original information signal from a modulated carrier signal is called ___________.

Modulation

before LF intelligence is transmitted through space it is modified to carry the information on a radio frequency signal, the process of adding info to an RF signal is called _____________.

Amplitude, Frequency, Phase

The basic characteristics of electrical signals are ___________________, ___________________, ___________________.

Carrier

Because it carries the intelligence, the RF signal is called a _________

Frequency

_________________ is the rate at which something occurs or is repeated over a particular period of time or in a given sample.

Amplitude

in AM, the ________ of the RF is varied in accordance to the intelligence

Sine wave or sinusoidal wave

___________________ is a mathematical curve that describes a smooth periodic oscillation (continuous wave)

sidebands

amplitude modulating a carrier produces signals higher and lower in frequency than carrier. These signals are called __________

Modulated signal

__________________ is the resultant signal after the process of modulation.

Angle Modulation `

Is the process of in which the frequency or the phase of the carrier varies according to the message signal.

Frequency Modulation `

Is the process of varying the frequency of the carrier signal linearly with the message signal

Phase Modulation `

Is the process of varying the phase of the carrier signal linearly with the message signal.

Frequency Deviation `

The amount of frequency change or the difference between the FM modulated frequency and carrier frequency.

Band Pass Filter `

Is a device that passes frequencies within a certain range and rejects frequencies outside that range.

535kHz, 545kHz

a 540 kHz signal is AM by a 5kHz signal. what are the frequency of USB and LSB?

10kHz

what is bandwidth of an AM if the carrier is 600kHz and intelligence is 5kHz

percentage of modulation

the percentage of the amplitude derivation from the normal value of the RF carrier is referred to as the __________________

66.6%

An AM waveform has a max amplitude of 100 Vp-p and a min amplitude of 20 Vp-p. The percentage of modulation is ___________

Overmodulation

Sometimes the modulating waveform is too high for the unmodulated carrier. In this case, the carrier is cut off for a period of each cycle of the modulating waveform. This condition is called _______________.

High Level Modulation

In some Tx, the modulator is the last stage before the antenna. This technique is called _______________.

Modulating signal

In low-power Tx, the modulator is often a transistor ckt, and the modulator acts as an amplifier to the carrier. However, the gain of the amplifier is controlled by the _________________.

Collector Modulation

 The modulation ckt often gets its name from the point at which the modulating signal is applied. e.g. , if the modulating signal is introduced in the collector ckt, the technique is called ___________________.

Demodulation

The purpose of the AM Receiver is to remove the modulation from the RF carrier. This process is called ______________

Diode Detector

The most popular ckt for demodulation is called a _____________________.

Intermediate Frequency

 Most receivers also contain a mixer stage, it heterodynes the received RF signal with a local oscillator signal to produce an _____________________.

Super Heterodyne Receiver

The receiver which uses the technique of heterodyning received RF signal with a local oscillator to produce IF is called a ______________________.

Frequency Converter

Often, the mixer and LO are combined in a single stage called a _____________________.

Carrier

A standard AM system transmits both sidebands and the ___________________.

Sidebands

 The carrier is a constant-amplitude, constant–frequency signal. Since the carrier does not change in any way when intelligence is added, the intelligence must be contained in the _________________

LSB

The USB contains the same intelligence as the _______________

bandwidth

The transmitted signal’s ______________ must be twice the highest frequency of the modulating signal.

carrier

 Most of the power in standard AM system is in the

SSB

The power and bw problems of standard AM can be overcome by an AM system called _______________.

Carrier and any of the sidebands

In SSB, the ________________ and the _________________ are eliminated by the transmitter.

balanced modulator

Generally, the carrier is eliminated by a circuit called a __________________________.

filter

The unwanted sideband is removed by a sharply-tuned ____________.

carrier

In SSB since no carrier is transmitted, a substitute ___________ must be reinserted in the receiver.

Beat Frequency Oscillator

The circuit that produces the substitute carrier at the receiver is called a _______________________.

carrier

In another form of AM, the carrier is suppressed but both sidebands are transmitted. Finally, a system called SSB-SC is sometimes used. In this system, a sample of the carrier is transmitted. Its purpose is to set the frequency of the substitute ____________ in the receiver.

Vestigial Sideband

The system used in television transmits the USB and the carrier without attenuation. However, the remaining components are attenuated so that only a part of the lower sideband remains. _________

Frequency

In AM systems, the amplitude of the carrier is varied in accordance with the MS. In FM systems, the ________________ of the carrier is varied.

Frequency

In FM, the rate at which the carrier deviates is determined by the __________________ of the modulating signal.

varactor

An FM signal can be reproduced by changing the frequency of an oscillator in step with a modulating signal. Often this is done with a special type of diode called ____________.

Slope Detector

 One type of FM detector looks like an AM detector that is slightly detuned. This ckt is called a ________________.

+- 75kHz

The range of deviation for 100% modulation in commercial FM broadcast.

88-108MHz

 The range of commercial FM broadcast.

1800s

Year discovered, Electrical energy can be transmitted through space

1870

Year, predicted the existence of radio waves

James Clerk Maxwell

 Physicist who developed a unified theory of electromagnetism

Heinrich Hertz

 Physicist, applied maxwell’s theory to the production and reception of radio waves.

1897

Year marconi, first practical wireless transmitter.

A,F,P

Basic characteristics of electrical signal.

Amplitude

The maximum extent of a vibration or oscillation measured from the position of equilibrium.

Frequency

The rate at which something occurs or is repeated over a particular period of time.

Phase

The relationship in time between the successive states of cycles of an oscillating or repeating system.

sine wave or sinusoidal wave

A mathematical curve that describes a smooth periodic oscillation.

Cosine wave

 Is a signal waveform with a shape identical to that of a sine wave, except each point occurs exactly ¼ cycle earlier than the sine wave.

Time-domain analysis/Representation

Gives the signal behavior over a certain time period

Frequency-domain representation

Signal is analyzed as a mathematical function with respect to the frequency.

20-20kHz

 Information frequency range.

533-1605 kHz

 AM freq range

136-174, 400-480 MHz

Citizen’s Band range or FRS

118-136 MHz

Air to ground comms range

108-118Mhz

DVOR and localizer range

328.6-335.4MHz

Glide path freq range

960-1215 MHz

DME freq range

Analog Modulation

Refers to the process of transferring analog LF over a HF carrier signals.

Digital Modulation

 Refers to the process of transferring digital LF like a digital bit stream over an HF carrier signal.

Flywheel Effect

The _______________ of the tank ckt produces the - half cycle for each positive input pulse in an AM.

band-pass filter

 Is a device that passes frequencies within a certain range and rejects frequencies outside that range.

Depth of Modulation, Mod index, coefficient of Mod

Is a value that describes the rel. between the amplitude of the modulating signal (total SB magnitude) and the amplitude of the carrier signal.

Overmodulation

A term described when the modulated waveform experiences a 180 degree phase reversal which causes addtl sidebands.

Non-linear, linear

THe modulation process is accomplished in a _______________ device but all circuitry that follows must be ________________.

Class C, Linear

What type of amplifiers are used in High-level? Low-level? (respectively)

Demodulator

Is a circuit where the intelligence must be recovered from the RF.

Detector

Is a device that recovers data of interest from a modulated wave.

Master Oscillator

In FM transmitter, the oscillator that determines the frequency is called a  ______________________.

Crystal-controlled Oscillator

Is used so that the output frequency of a local oscillator in an FM Tx is extremely stable.

Carrier swing

The deviation of the frequency of the carrier signal from high to low or low to high

Frequency Deviation

The amount of frequency change or the difference bet the FM modulated frequency and the carrier freq.

Major Edwin Armstrong - 1936, 1939

 Who developed first working FM system and when? What year began the scheduled FM broadcast?

amplitude

The amount that the carrier deviates from its center frequency is determined by the ____________ of the modulating signal.

Slope Detector

This is a very simple form of FM demodulation and it relies on the selectivity of the receiver itself to provide the demodulation.

Foster-Seeley Discriminator

Uses double-tuned RF transformer to convert the instantaneous variations of the FM input signal to instantaneous amplitude variations.

Foster-Seeley Discriminator

Also called a phase-shift discriminator.

FM Ratio Detector

Uses double-tuned transformer to convert the instantaneous frequency variations of the FM input signal to instantaneous amplitude variations. These amplitude variations are then rectified to provide a DC output voltage which varies in amplitude and polarity with the input signal.

Space Modulation

Is a modulation process wherein the sidebands are combined with the carrier in space or outside the transmitting equipment.

harmonics

If phi is other than 0 or 180, The sideband is not in-phase with carrier and the ________________ of the modulating frequency will be produced.

90 degrees

At what angle will the harmonic magnitude be maximum in space modulation?

Space Modulation

Is the process by which separately radiated sidebands combine in space with a carrier.

Ratio of Distortion

What do you call the ratio between the second harmonic to useful signal? (space modulation)

90 Degrees

The ratio of distortion becomes a maximum at a phase difference of _____.

Angle modulation

Is the process in which the fequency or the phase of the carrier varies according to the message signal

Modulation

The process of altering the characteristics of the amplitude, frequency, or phase angle of the high-frequency signal in accordance with the instantaneous value of the modulating wave is called _________________.

James Clerk Maxwell

Scottish physicist ____________________ predicted the existence of radio waves. He developed a unified theory of electromagnetism.

Analog Modulation

_________________ refers to the process of transferring analog low frequency baseband signal, like an audio or TV signal over a higher frequency carrier signal such as a radio frequency band.

Amplitude

_________________ is the maximum extent of a vibration or oscillation measured form the position of equilibrium.

Time domain representation, Frequency domain representation

Electrical signal is represented by ________________, ________________.

Carrier signal

__________________ is the high frequency signal which has a certain phase, frequency, and amplitude but contains no information.