Ch 16Communication Systems — Class 12 Physics, concept-first.

Communication is the act of transferring information from one point (the sender) to another (the receiver), and it can only succeed when both share a common code or language to encode and decode the m…

Every communication system - no matter what it carries or how - is built from three essential blocks, with noise capable of entering and degrading the signal at any point along the way.

- Transducer - any device that converts one form of energy into another. An electrical transducer specifically converts a physical quantity such as pressure, displacement, force or temperature into a…

Different message signals need different ranges of frequencies to be represented faithfully, and the communication system required depends on which band is needed.

Just as a signal occupies a certain bandwidth, a transmission medium can only carry a certain bandwidth.

Once a transmitting antenna radiates an electromagnetic wave, its strength keeps decreasing as it travels away from the transmitter towards the receiving antenna.

For an antenna to radiate a signal efficiently, its physical size should be comparable to the signal's wavelength - at least about . At long wavelengths (i.e.

For frequencies from roughly a few MHz up to about 30-40 MHz, long-distance communication becomes possible because radio waves can be reflected back down to earth by the ionosphere - this is sky-wave…

A third propagation mode is the space wave, which travels in a straight line directly from the transmitting antenna to the receiving antenna.

The purpose of any communication system is to carry the information or message signal - also called the baseband signal - which is the band of frequencies that represents the signal exactly as it is d…

Transmitting a signal efficiently requires an antenna whose physical size is comparable to the signal's wavelength - at least about .

For a linear antenna of length , theory shows that the power it radiates is proportional to . This means that for an antenna of fixed length, the radiated power increases as the wavelength shrinks - i…

A third, more practical, problem arises when many transmitters send out baseband information signals simultaneously: since all these signals occupy roughly the same low-frequency range, they overlap a…

In amplitude modulation (AM), the amplitude of the carrier wave is varied in proportion to the instantaneous value of the message signal, while the carrier's frequency stays fixed.

A conceptually simple way to generate an AM wave is to first add the modulating signal to the carrier:

As the transmitted signal travels through the channel, it gets attenuated, so at the receiving end the antenna's output must first pass through an amplifier before anything else can be done with it.

Solved examples, worked out step by step.

Sample papers and previous-year board questions for this subject.