Question

What is the longest wavelength of audio signals to be transmitted in communication
system? Why can't we transmit these signals directly at long distances? Give any two
reasons. What is done to transmit them to long distances.

Answer 1

Dear Student

A few kilometers

​​​​​​​ Reasons
i Due to their low frequency range audio signals radiated directly from antenna die out after travelling some distance .
(ii) Height of antenna required is impractically large .
(iii) Audio signals transmitted from different stations get inseparably mixed up .


Methods
Audio signals can be directly transmitted through the space this is because the optimum length of the radio antenna is half or quarter of a wavelength. And typical wavelength of audio signals is around few hundreds killometers, hence very large antennas are required.
So to transmit the audio signal, it is modulated with the carrier wave having radio frequency. This is frequency modulation.
Other than this amplitude modulation and phase modulation are also used.

Regards