The radio horizon of a transmitting antenna of height $39.2 \ m$ is (Radius of the earth $= 6400 \ km$) (in $km$)

Which of the following four alternatives is not correct? We need modulation:

For commercial telephonic communication,the frequency range adequate for speech signals is

An audio signal consists of two distinct sounds: one is a human speech signal in the frequency band of $200\,Hz$ to $2700\,Hz,$ while the other is a high-frequency music signal in the frequency band of $10200\,Hz$ to $15200\,Hz.$ The ratio of the $AM$ signal bandwidth required to send both the signals together to the $AM$ signal bandwidth required to send just the human speech is

Radio waves of constant amplitude are produced by a/an . . . . . . .

For a coaxial cable,the typical repeater spacing is approximately............$km$.