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A separate high freq. wave (i.e. carrier...

A separate high freq. wave (i.e. carrier wave) is needed in modulation why ?

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This is because we cannot any of the characterostics (amplitude, frequency or phase) of the audio signal as this would change the message to be communicated. So keeping the audio signal same, the amplitude of freq. or phase of the high freq. carrier wave is modified in accordance with the modulating (i.e. audio signal) signal.
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The efficient transmission of signals is achieved by superimposing electrical audio signals on a high frequency carrier wave (the process is known as modulation). When the amplitude of high frequency carrier wave is changed in accordance with the intensity of modulating signal, it is called amplitude modulation. The extent to which the amplitude of carrier wave is changed by the signal is described by modulation factor. It is given as m="Amplitude change of carrier wave"/"Amplitude of unmodulated carrier wave" Let a carrier wave is represented by V_c=V_c cos omega_ct Let the modulation factor be m, the maximum change in amplitude of carrier wave is mV_c So, modulating signal can be represented as v_m=mV_c cosomega_mt So, the amplitude of modulated wave is =V_c+mV_c cosomega_m t Using this value, the instantaneous voltage of modulated wave is E=V_c cos omega_c t+ (mV_c)/2 cos (omega_c+omega_m)t + (mV_c)/2 cos (omega_c-omega_m ) t The above wave contains three frequencies namely, f_c, f_c+f_m and f_c-f_m . The frequencies f_c+f_m and f_c-f_m are called side band frequencies , USB and LSB respectively. The fraction of total power carried by side band frequencies is

Both amplitude modulation (AM) and frequency modulation (FM) are used for radio broadcasting. The amplitude of the high frequency carrier wave is varied or modulated in accordance with the variations in the amplitude of the audio signals that are to be transmitted, in te process of amplitude modulation in frequency modulation te amplitude of the carrier remains constant but its frequency is varied inn accordance withh the audio signal. Reception with AM signals is in general is affected by interference of various kinds ad elaborated equipment is required for FM broadcast. A radio frequency carrier wave can be modulated using a-

Assertion : Higher the modulation index the reception will be strong and clear. Reason : The degree, to which the carrier wave is modulated is called modulation index.

Calculate the power developed by an amplitude modulated wave in a load resistance of 100 Omega , if the peak voltage of carrier wave is 100 V and modulation index is 0.4.

Modulation is the phenomenon of superimposing the low audio frequency base band message or information signals ( called the modulation signals) on a high frequency wave (called, the carrier wave). The resultant wave is called the modulated wave, which is transmitted. Read the above passage and answer the following questions: (i) What are the Audio Frequency and Radio Frequency ranges? (ii) Why audio frequency signals, as such cannot be transmitted over long distance? (iii) What does the phenomemom imply in day to day life ?

The device used for addition of high frequency carrier wave and information signal is

The process in which frequencies of carrier wave changes in accordance with instantaneous value of modulated signal is

The process by which some characteristics i.e. amplitude, phase or frequency of hight frequency carrier wave is varied with information signal is

ALLEN-WAVES AND OSCILLATIONS-Part-3(Example)
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  16. A ground reciver is receiving a signal at (a) 5 MHz, and (b) 100 MHz, ...

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  17. A separate high freq. wave (i.e. carrier wave) is needed in modulation...

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  18. A message signal of frequency 10kHz and peak voltage of 10"volts" is u...

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  19. The modulation index of an FM carrier having a carrier swing of 200kHz...

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