Commonly used terms in electronic communication system - class-XII

The communication and broadcasting following the base on generation, propagation, and detection of electromagnetic waves.

The electromagnetic spectrum describes a different range of electromagnetic waves. These EM waves are a special type of wave that can travel without a medium.

Electromagnetic waves are named like this due to the fact that they have both an electric and a magnetic component. In a vacuum, EM waves always travel at the same speed i.e. the speed of light. So, other EM waves besides light are infrared, ultraviolet, radio waves, and microwaves. Therefore radio and television both are based on EM wave properties. Other options like lasers, reactors, and computers are not guided by EM waves.

Thus the correct option is C. 

Attenuation means reduction of strength of signal, thus signals are to be amplified.

In this case transducer takes the sound signal and convert them to electrical signal.

Signals which need to be transferred are superimposed on high frequency wave, which is called carrier wave, as the name suggests it carries the signals.

Loudspeaker is a transducer which converts electrical signal transmitted by the transmitter to sound form at the receiving end.

The message from the information source may not be in electrical form, so to convert these information, i.e., in form of sound to electrical form, a transducer like a microphone is used.

The received signals is either AM or FM so it needs to be demodulated, ie., decoded to get back original signal. It also needs to be stored and interpreted at receiving end.

A superheterodyne receiver is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency.

Man-made noise is a noise created due to wear and tear of electrical machinery used in transmission systems. They are due to the type of amplifiers (class B) type of pulses (wideband pulses), often caused by ignition circuits, lightning, and switching elements causing spark gaps

Thermal noise or Nyquist noise is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage.

In each of the options, an electrical element is used and hence this noise is produced in all these elements. The correct option is option D

Shortwave radio or radio waves are used for broadcasting of voice and music to listeners over very large areas. Which uses a layer in the atmosphere called the ionosphere for the refraction and reflection purpose.

SNR in dB is 10log10(S/N). If bandwidth doubles, noise power N doubles (assuming white noise), so S/N becomes S/(2N). The new SNR is 10log10(S/2N) = 10log10(S/N) - 10log10(2) = 30 - 3 = 27 dB.

Modulation index m = Vm/Vc = 5/25 = 0.2. Sidebands are at fc + fm and fc - fm, which are 1200 + 20 = 1220 kHz and 1200 - 20 = 1180 kHz.

A device which converts energy in one form to another is called a transducer. Usually a transducer converts a signal in one form of energy to a signal in another. The process of converting one form of energy to another is known as transduction.
In radio communication, microphone is used to convert sound signal into electrical signal. Hence the microphone acts as a transducer.

According to definitions use in communication systems: 
Antenna: A device that radiates signals. (Option h)
Transmitter: As the name suggests, it transmits (sends) out information. (Option e)
Receiver: As the name suggests recieves (pick ups) the information. (Option f)
Transducer: A device that converts variations in a physical quantity, such as pressure or brightness, into an electrical signal, or vice versa. That is option g.

The range of a TV tower is d = sqrt(2Rh). To double d, the height h must be multiplied by 4, because sqrt(4) = 2.

Waves emitted by a radio transmitter are usually linearly polarized. The vertical antennas that are used for radio broadcasting emit waves that, in a horizontal plane around the antenna, are polarized in the vertical direction parallel to the antenna.

The total voltage gain of amplifiers in series is the product of individual gains: 10 * 20 * 30 = 6000. With an input peak signal of 1 mV (0.001 V), the theoretical output peak signal is 6000 * 0.001 V = 6 V. Since the DC supply voltage is 10 V, the output is safely clipped or within the supply rails at 6 V.

Radio signals are electromagnetic waves that travel at the speed of light, which is immensely faster than the speed of sound waves in air. Therefore, the radio signal from 100 m away will be heard and detected well before the sound of a person yelling.

Noise is the unwanted energy and distortion both occurring at various stage of a system leads to deterioration of signal, as signal to noise ratio becomes so poor that signal becomes unintelligible and useless.

A receiver receives the pre-modulated signal through receiving antenna, demodulates it using demodulator, and finally amplifies it to be sent as output to loudspeaker etc.

The Range of frequency for the signals which is used for transmitting videos is called video frequency or VF frequency bandwidth .It ranges between 0 and the highest frequency used to transmit a live telivision image

When audio signals are transmitted over thousands of kilometres through
radio transmission, the audio frequencies that lie within the frequency
range of 15 Hertz to 20 KiloHertz has very small signal power and thus
cannot be transmitted via antenna for communication purposes. The
radiation of electrical energy is only possible at frequencies above 20
KiloHertz.  Thus, the audio signals must be sent along with the high
frequency signals for communication since the high frequency signals can travel long distance without dissipation in power. This can be done by superimposing
electrical audio signals on a high frequency wave called the carrier
wave by a process called modulation.

The generally accepted standard range of audible frequencies is $20 Hz$ to $20,000 Hz$, although the range of frequencies individuals hear is greatly influenced by environmental factor. Frequencies below $20 Hz$ are generally felt rather than heard, assuming the amplitude of the vibration is great enough. Frequencies above $20,000 Hz$ ($20 kHz$) frequencies are the first to be affected by hearing loss due to age and prolonged exposure to very loud noises.

Tuned frequency is $91.6MHz$ and corresponding oscillator frequency is $102.3MHz$. Then image frequency is $102.3+10.7 MHz = 113MHz$