The modulation index for an $A.M.$ wave having maximum and minimum peak-to-peak voltages of $14\,mV$ and $6\,mV$ respectively is:

Match List $I$ with List $II$ :

List $I$	List $II$
$A$. Attenuation	$I$. Combination of a receiver and transmitter.
$B$. Transducer	$II$. Process of retrieval of information from the carrier wave at receiver.
$C$. Demodulation	$III$. Converts one form of energy into another.
$D$. Repeater	$IV$. Loss of strength of a signal while propagating through a medium.

Choose the correct answer from the options given below:

$A$ $25\, m$ long antenna is mounted on an antenna tower. The height of the antenna tower is $75\, m$. The wavelength (in meter) of the signal transmitted by this antenna would be

The frequency suitable for beyond-the-horizon communication using sky waves is

In satellite communication,the uplink frequency band used is

$A$ communications Earth satellite: