Question

why high frequency carrier waves are needed for effective transmission of information signals

Answer 1

1) For transmitting wave of wavelength x, the length of transmitting antennae must be comparable to x, around x/4. For higher wavelengths, like 4km, this would be cumbersome and uneconomical. So, wavelength must be reduced, i.e. Frequency is to be increased.

2) Power transmitted is inversely proportional to square of wavelength of the signal wave. So, shorter wavelength increases power, which means higher frequency.

3) When multiple signal waves are transmitted in same low frequency zone, there is chance for them to interfere with each other and cause signal disturbances. So, it is better to allocate individual high frequency wave bandwidths for each channel, thus reducing attenuation and unnecessary interference of signals.

Due to all above reasons, signal wave is modulated onto a carrier wave of higher frequency.