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An audio signal of 15 kHz frequency cann...

An audio signal of 15 kHz frequency cannot be transmitted over long distance without modulation because.

A

the size of the required antenna would be at least `5 km` which is not convenient

B

the audio signal can not be transmitted through sky waves.

C

the size of the requried antenna would be at least `20 km`, which is not convenient

D

effective power transmitted would be very low, if the szie of the antenna is less than `5km`.

Text Solution

Verified by Experts

The correct Answer is:
A, B, D
Here `f=15kHz=15xx10^(3)Hz`
`lambda=(c )/(f)=(3xx10^(8))/(15xx10^(3))=(1)/(5)xx10^(5)`
Size of the antenna should be at least `l=(lambda)/(4)=5km`
Audio signal cannot be transmitted through the sky waves, because in sky wave propagation the frequency range is `2 MHz` to `40 MHz`. But frequency of this wave is `15KHz`.
For the effective power radiation by the antenna
`P prop ((L)/(lambda))^(2)`
if `L` decreases `p` also decrease.
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