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Question

how do antennas work effectively when their dimension is of the order of wavelength of signal being transmitted??

also what is electrical analog of audio tone?how audio tone is converted into its electrical analog

give me concept guyzz i dont understand this frm book

Answer 1

When a car passes your house with bad spark plugs (arcing, etc.) it creates static that your radio can pick up.  An antenna helps to efficiently transmit a similar electrical signal except that it is generally sinusoidal in nature.  Being sinusoidal it has a definite wave length and can best be transmitted by an antenna (wire?) that is a full or partial wavelength long (like striking a tuning fork produces a certain frequency).

An electrical analog of an audio tone results when the electrical signal has a similar shape to the audio wave form (and is therefore analogous to it).  For AM radio, a carrier wave is transmitted but its amplitude (strength) is varied (modulated) analogous to the shape of the audio (vocal, music, etc.) wave form.  For FM, the frequency of the carrier wave is varied (modulated) to be analogous to the audio input.

  

Answer 2

Radio waves can be miles in length, antennas pick up the frequency of the waves. A variable capacitor in the radio is tuned to pick up a particular frequency. A circuit called a super hetrodyne converts the signal into pulses that are sent to the radio speaker.