What is digital modulation? Describe briefly its methods.

In digital modulation, an analog carrier signal is modulated by a digital bit stream. Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet).

Fundamental digital modulation methods

These are the most fundamental digital modulation techniques:

• In the case of PSK, a finite number of phases are used.
• In the case of FSK, a finite number of frequencies are used.
• In the case of ASK, a finite number of amplitudes are used.
• In the case of QAM, a finite number of at least two phases, and at least two amplitudes are used.

In QAM, an inphase signal (the I signal, for example a cosine waveform) and a quadrature phase signal (the Q signal, for example a sine wave) are amplitude modulated with a finite number of amplitudes, and summed. It can be seen as a two-channel system, each channel using ASK. The resulting signal is equivalent to a combination of PSK an

In digital modulation, an analog carrier signal is modulated by a digital bit stream. Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet).

Fundamental digital modulation methods

These are the most fundamental digital modulation techniques:

• In the case of PSK, a finite number of phases are used.
• In the case of FSK, a finite number of frequencies are used.
• In the case of ASK, a finite number of amplitudes are used.
• In the case of QAM, a finite number of at least two phases, and at least two amplitudes are used.

In QAM, an inphase signal (the I signal, for example a cosine waveform) and a quadrature phase signal (the Q signal, for example a sine wave) are amplitude modulated with a finite number of amplitudes, and summed. It can be seen as a two-channel system, each channel using ASK. The resulting signal is equivalent to a combination of PSK and ASK.

In all of the above methods, each of these phases, frequencies or amplitudes are assigned a unique pattern of binary bits. Usually, each phase, frequency or amplitude encodes an equal number of bits. This number of bits comprises the symbol that is represented by the particular phase.

If the alphabet consists of M = 2^N alternative symbols, each symbol represents a message consisting of N bits. If the symbol rate (also known as the baud rate) is f_S symbols/second (orbaud), the data rate is Nf_S bit/second.

For example, with an alphabet consisting of 16 alternative symbols, each symbol represents 4 bits. Thus, the data rate is four times the baud rate.

In the case of PSK, ASK or QAM, where the carrier frequency of the modulated signal is constant, the modulation alphabet is often conveniently represented on a constellation diagram, showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-axis, for each symbol.

d ASK.

In all of the above methods, each of these phases, frequencies or amplitudes are assigned a unique pattern of binary bits. Usually, each phase, frequency or amplitude encodes an equal number of bits. This number of bits comprises the symbol that is represented by the particular phase.

If the alphabet consists of M = 2^N alternative symbols, each symbol represents a message consisting of N bits. If the symbol rate (also known as the baud rate) is f_S symbols/second (orbaud), the data rate is Nf_S bit/second.

For example, with an alphabet consisting of 16 alternative symbols, each symbol represents 4 bits. Thus, the data rate is four times the baud rate.

In the case of PSK, ASK or QAM, where the carrier frequency of the modulated signal is constant, the modulation alphabet is often conveniently represented on a constellation diagram, showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-axis, for each symbol.

What are the applications of DSB-SC modulation?

Applications:

- Analogue TV systems: to transmit color information.

- For transmitting stereo information in FM sound broadcast at VHF

- One important application of DSB is the transmission of color information in a TV signal.

- CB radio

- TV broadcasting

- Air traffic control radios

- Garage door opens keyless remotes

- DSB-SC is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.

- DSB-SC used in stereo transmission of FM radio.

- Two way radio communications.

What is sidebands ?

sideband: One of two frequency bands on either side of the carrier wave, containing the modulated signal.

In electronic signal transmission, a sideband is the portion of a modulated carrier wave that is either above or below the basic ( baseband ) signal. The portion above the baseband signal is the upper sideband ; the portion below is the lower sideband . In regular amplitude modulation ( AM ) transmission, both sidebands are used to carry a message. In some forms of tranmission, one sideband is removed ( single-sideband transmission ) or a portion of one sideband is removed.

Write down the difference between AM,FM and Digital signals?

Write Down the comparison between STS & TST networks?

Comparison between STS & TST networks:

What is STS switching? Write down important features of our STS.

Static Transfer Switch (STS): Static Transfer Switch (STS) is an electrical device that switches between two power sources without delay.

Based on Current & Voltage capacity of STS, it is classified as Low Voltage STS (LV-STS) & Medium Voltage STS (MV-STS). LV-STS have current rating from 50A to 4000A & voltage up to 600V.

Some of the important features of our STS are as follow:

·         Increased power quality

·         Easy monitoring all parameters on LCD display

·         Fast microcontroller. Power blackout protection

·         Automatic static switching. Remote monitoring of input power sources

·         Easy static and mechanical transfer between separate input sources

·         Remote management of power events. Power event logging

·         Advanced RS232 communication features. DRY contact alarm interface

·         Password protected login system from remote site (timed Access)

·         2 redundant power supplies form electronic boards (hot swappable)

·         Easy front access to all components inside of the STS

·         Second protection cover on live circuits which prevents electrical shock

·         Input sources protected by fuses

·         3 positioned Maintenance bypass switch which prevents cross currents between input sources

·         User adjustable parameters by entering a password. Built in real time clock

·         history (with their date and time)

·         Automatic transfer test from a remote site or using front panel. Front panel Lamp test

·         External emergency shutdown (EPO) input

·         Hot plug construction during maintenance bypass

·         High current output tolerant up to 1000%.

·         Temperature sensor inside the Cabinet

What is QAM?

Quadrature Amplitude Modulation: A modulation technique that generates four bits out of one baud. For example, a 600 baud line (600 shifts in the signal per second) can effectively transmit 2,400 bps using this method. Both phase and amplitude are shaped with each baud, resulting in four possible patterns. Using two carriers out of phase by 90° and modulated by separate signals.