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Learn about the fundamental principles of communication systems, including signal processing, receiving and processing of information by electronic means.
Analog signal may be converted into digital signal by
AM was the earliest modulation method used for transmitting audio in radio broadcasting. It was developed during the first quarter of the 20th century beginning with ___and Reginald Fessenden's.
Calculate the modulation index when the un modulated carrier power is 15KW, and after modulation, carrier power is 17KW.
Convert power gains of 0.01, 0.001, and 0.0005 to decibel values
When does over-modulation occur?
When this _____________ is exposed to radio waves, the waves induce a very small alternating current in the antenna.
What is the reference line for the modulating signal?
Like all electromagnetic waves, ____in a vacuum travel at the speed of light, and in the Earth's atmosphere at a close, but slightly lower speed.
This method simply requires the use of a varactor diode placed within the tuned circuit of an oscillator circuit.
These transmissions could offer high fidelity audio, and for this reason, frequency modulation is far more popular than the older transmissions on the long, medium and __.
Emitter modulator amplifier for Amplitude Modulation
Convert decibel power gains of 13 dB, 33 dB, and 103 dB to power gains.
The ___varies in accordance with the instantaneous amplitude of the modulating signal.
Noise figure of merit in SSB modulated signal is
In_____, carries video using two synchronized signal and ground pairs, termed Y and C.
Calculate the power in one of the side band in SSBSC modulation when the carrier power is 124W and there is 80% modulation depth in the amplitude modulated signal.
A power amplifier has a gain of 55 dB. The input power is 600 mW. What is the output power in W?
Convert power gains of 100, 1000 and 2000 to decibel values
Captures the radio waves.
The ratio between the modulating signal voltage and the carrier voltage is called?
In_____, the amplitude of the carrier wave is varied in proportion to that of the message signal being transmitted.
For over modulation, the value of modulation index m is
TRF receiver and super heterodyne receiver are used for
__is the process of converting a digital bit stream into an analog carrier wave for transmission via a communication channel.
In Amplitude Modulation, the instantaneous values of the carrier amplitude changes in accordance with the amplitude and frequency variations of the modulating signal.
This frequency, called the _____________, is determined by the values chosen for the coil and the capacitor.
What is the effect of distortion?
The process of transforming a carrier signal so that it can carry the information of a message signal.
______system depends on light as the medium for communication.
Creates alternating current at the frequency on which the transmitter will transmit.
______________ FM (NBFM) often uses deviation figures of around ±3 kHz.
What is the circuit used for producing AM called?
The more powerful the __, the more powerful the broadcast.
If a receiver has poor capacity of blocking adjacent channel interference then the receiver has
A 3 GHz carrier is DSB SC modulated by a signal with maximum frequency of 2 MHz. The minimum sampling frequency required for the signal so that the signal is ideally sampled is
An amplifier has an output power of 5W. What is this amount of power in dBm?
Optical communication system depends on___ as the medium for communication.
When AM signal is of 25KHz, calculate the number of channels required in Medium Frequency (MF) band of 300KHz-3000KHz.
The ability of the receiver to select the wanted signals among the various incoming signals is termed as
When the _______________ is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency.
A __ consists of several elements that work together to generate radio waves that contain useful information such as audio, video, or digital data.
The ______________ by which the signal moves up and down is important.
It uses an antenna to capture radio waves, processes those waves to extract only those waves that are vibrating at the desired frequency, extracts the audio signals that were added to those waves, amplifies the audio signals, and finally plays them on a speaker.
Aliasing refers to
Whether for __ or mobile radio communication systems, or for use in portable applications, FM is widely used at VHF and above.
As with any form of ______________, it is necessary to be able to successfully demodulate it and recover the original signal.
What is the condition for greatest output power at the transmitter without distortion?
It is not possible to change the frequency of a signal to give frequency modulation or FM.
___ filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency.
Unless you want to listen to every radio channel at the same time, you need a circuit that can pick out just the signals for the channel you want to hear. That’s the role of the ____________.
Modulation is required for
On its own(tuner), the antenna captures ______________ of all frequencies and sends them to the RF amplifier, which dutifully amplifies them all.
Calculate the depth of modulation when a transmitter radiates a signal of 9.8KW after modulation and 8KW without modulation of the signal.
What is the carrier frequency in an AM wave when its highest frequency component is 850Hz and the bandwidth of the signal is 50Hz?
More sophisticated tuners use a variable capacitor (also called a ______________) to vary the frequency.
Provides the necessary electrical power to operate the transmitter.
A range of frequencies within a given band, in particular that used for transmitting a signal.
The amplitude of the carrier signal containing ____varies as per the amplitude of the signal containing information, at each instant.
An unmodulated AM signal produces a current of 5.4 A. If the modulation is 100 percent, calculatesada) the carrier power, (b) the total power, (c) the sideband power when it is transmitted through an antenna having an impedance of 50Ω.
A power amplifier has an output power of 200 W and an input power of 8W. What is the power gain in decibels?
The first, called __ or AM, makes slight increases or decreases to the intensity of the carrier wave.
In the later part of the 19th century, scientists figured out how to electronically generate __ using electric currents.
This is a particular frequency at which the attenuation reaches a specified value.
Adds useful information to the carrier wave.
______use analog and Frequency Division Multiplexing.
Amplitude modulation is
For _______________, less bandwidth is used.
An AM transmitter has an antenna current changing from 5 A un modulated to 5.8 A. What is the percentage of modulation?
The total power in an Amplitude Modulated signal if the carrier of an AM transmitter is 800 W and it is modulated 50 percent.
_____affects the propagation of waves and signals in electrical circuits, in optical fibers, and in air. Electrical attenuators and optical attenuators are commonly manufactured components in this field.
The _____________ may be called a variety of names including FM demodulator, FM detector or an FM discriminator.
In the TV receivers, the device used for tuning the receiver to the incoming signal is
The function of multiplexing is
What is the overall gain in dB (AT,dB)?
What is the percentage of modulation if the modulating signal is of 7.5V and carrier is of 9V?
The modulation technique that uses the minimum channel bandwidth and transmitted power is
Disadvantage of using a DSB or SSB signal modulation is
It is possible to apply the modulation to a _____________, and it is not necessary to use a linear form of amplification to increase the power level of the signal to its final value.
Which is not a kind of Analog modulation ?
It is often necessary to manage the constraints within the loop carefully but once done it provides and excellent solution.
Calculate the bandwidth occupied by a DSB signal when the modulating frequency lies in the range from 100 Hz to 10KHz.
A ____filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency.
An AM signal has a total power of 48 Watts with 45% modulation. Calculate the power in the carrier and the sidebands.
__is the attenuation of radio energy between the feed points of two antennas that results from the combination of the receiving antenna's capture area plus the obstacle-free, line-of-sight path through free space.
Frequency modulation is particularly well known for its use for VHF FM broadcasting.
Synchronous detection means
Calculate the frequencies available in the frequency spectrum when a 2MHz carrier is modulated by two sinusoidal signals of 350Hz and 600Hz.
The AM spectrum consists of
____are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared radiation.
To generate a __, the frequency of the radio carrier is changed in line with the amplitude of the incoming audio signal.
Two components are required for radio communication: a transmitter and a __.
The second, called __ or FM, makes slight increases or decreases the frequency of the carrier wave.
When the __ is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency.
The amount of data transmitted for a given amount of time is called
NTSC means ____.
A radio receiver is the _____________ of a radio transmitter.
What is the effect on the transmitted power of AM signal when the modulation index changes from 0.8 to 1?
The type of system where the sender has to stop sending the signals to the recipient and then only the recipient can respond
An AM broadcast station transmits modulating frequencies up to 6 kHz. If the AM station is transmitting on a frequency of 894 kHz, the values for maximum and minimum upper and lower sidebands and the total bandwidth occupied by the AM station are:
In half Duplex communication system, both the two parties can’t communicate simultaneously.
______which is an international, non-profit organization developing voluntary standards for digital television.
In addition to its widespread use for high quality audio broadcasts, FM is also used for a variety of __ radio communication systems.
It is narrow band FM that is typically used for two-way radio _________________.
Advantage of using VSB transmission is
One particular advantage of frequency modulation is its resilience to _____________.
It is known as the deviation and is normally quoted as the number of ______________ deviation.
Continuous, unmodulated carrier, formerly common for radio direction finding in marine and aeronautical navigation.
Types of analog modulation are:
Usually ______________ is allowed for each wide-band FM transmission.
If an AM signal is represented by v = ( 15 + 3 Sin( 2Π * 5 * 103 t) ) * Sin( 2Π * 0.5 * 106 t) volts. (i) Calculate the values of the frequencies of carrier and modulating signals. (ii) Calculate the value of modulation index. (iii) Calculate the value of bandwidth of this signal.
The __ varies according to the changes in the environmental conditions and other situations.
The antenna current of the transmitter is 10A. Find the percentage of modulation when the antenna current increases to 10.4A.
__is a type of radio receiver used as a component of a radio communication link.
__ carry the information transmitted by the radio signal.
The ___ carry the information transmitted by the radio signal.
Broadcast stations in the VHF portion of the frequency spectrum between _____________ use large values of deviation, typically ±75 kHz.
What is the line connecting the positive and negative peaks of the carrier waveform called?
Radio communication system works even without the aid of an antenna.
Super heterodyne receivers
Frequency modulation is able to provide near interference free reception, and it was for this reason that it was adopted for the VHF sound broadcasts.
With____, in which the frequency of the carrier signal is varied.
A modulation index of 0.5 would be same as
What happens when the amplitude of the modulating signal is greater than the amplitude of the carrier?
If the input power is 1 dBm, what is the output power in dBm?
his component’s job is to amplify the weak signal that comes from the detector so that it can be heard. This can be done using a simple ______________.
FM speech communication , often used for marine radio and many other VHF communications.
Function of RF mixer is
Standard intermediate frequency used for AM receiver is
Bandwidth required in SSB-SC signal is (fm is modulating frequency):
Responsible for separating the audio information from the carrier wave.
What is SNRdB?
Antenna - RF amplifier - tuner - detector - audio amplifier - _____________
What’s left after the diode has its way with the alternating current signal is a direct current signal that can be fed to an ______________.
Type of communication system where two equipments can communicate with each other in both the directions simultaneously
Calculate the side band power in an SSBSC signal when there is 50% modulation and the carrier power is 50W.
In Amplitude Demodulation, the condition which the load resistor R must satisfy to discharge capacitor C slowly between the positive peaks of the carrier wave so that the capacitor voltage will not discharge at the maximum rate of change of the modulating wave (W is message bandwidth and ω is carrier frequency, in rad/sec ) is
In simple ______________, the tuning is adjusted by varying the number of turns of wire in the coil.
What is the SNR?
Radio waves have frequencies as high as ____to as low as 30 hertz.
A circuit that can extract signals of a particular frequency from a mix of signals of different frequencies.
Advantage of using a high frequency carrier wave is
Analog communication indicates:
What is the change in the value of transmitted power when the modulation index changes from 0 to 1?
____the corresponding wavelength is 10,000 km.
Calculate the power saved in an Amplitude Modulated wave when it is transmitted with 45% modulation – Without carrier, – Without carrier and a sideband
A sensitive amplifier that amplifies the very weak ________________ signal from the antenna so that the signal can be processed by the tuner.
If the value is less than 1, the modulation index is 0.5, then the modulated output would be called as___.
For low level modulation, amplifier used is
For _____________, this can be done with a diode that just rectifies the alternating current signal.
Baseband transmissions use digital signaling and ____.
While changing the amplitude of a radio signal is the most obvious method to modulate it, it is by no means the only way.
The positive and negative peaks of the carrier wave, are interconnected with an imaginary line. This line helps recreating the exact shape of the modulating signal. This imaginary line on the carrier wave is called as ___.
The oscillator usually generates a sine wave, which is referred to as a __.
In this mode of communication, the information is sent through light.
_____is the process of transforming a carrier signal so that it can carry the information of a message signal. It superimposes the contents of the message signal over a high-frequency carrier signal, which is then transmitted over communication channels.
The ____________ is simply a length of wire.
A receiver’s sensitivity is the minimum received signal power for the receiver to successfully recover the transmitted signal. If a receiver’s sensitivity is -45 dBm, and the received power is 10 μW, will the receiver be able to recover the transmitted signal?
Having a narrower band it is not able to provide the high quality of the _____________, but this is not needed for applications such as mobile radio communication.
Radio waves have frequencies as high as _____to as low as 30 hertz.
Calculate the total modulation Index when a carrier wave is being modulated by two modulating signals with modulation indices 0.8 and 0.3.
Many receivers include_____________ to better lock on to the intended frequency — or to produce better-quality audio output — and exclude other signals.
The tuner usually employs the combination of an ____________ (for example, a coil) and a capacitor to form a circuit that resonates at a particular frequency.
This is a method of combining more than one signal over a shared medium.
You can adjust the ______________ by varying the amount of inductance in the coil or the capacitance of the capacitor.
The overall power gain (AT)?
Three amplifiers with gains of 12.5, 4, and 20 are cascaded as shown in the following diagram (from left to right). The input power is 120 mW. What is the overall gain and the output powers of each stage?
Frequency modulation is widely used on frequencies below 30 MHz.
Calculate the power in a DSB SC signal when the modulation is 60% with a carrier power of 600W.
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