If $f_a$ and $f_f$ represent the carrier wave frequencies for amplitude and frequency modulations respectively,then

Match Column $A$ (layers in the ionosphere for skywave propagation) with Column $B$ (their height range).

Column $A$	Column $B$
$A$. $D$-layer	$I$. $250-400 \ km$
$B$. $E$-layer	$II$. $170-190 \ km$
$C$. $F_1$-layer	$III$. $95-120 \ km$
$D$. $F_2$-layer	$IV$. $65-75 \ km$

During modulation,a transmitter supplies $9 \ kW$ to the antenna. Calculate the total power radiated during $40\%$ modulation in $kW$.

In a communication system operating at a wavelength of $800\,nm,$ only one percent of the source frequency is available as signal bandwidth. The number of channels accommodated for transmitting $TV$ signals of bandwidth $6\,MHz$ is (Take velocity of light $c = 3 \times 10^8\,m/s$)

While tuning in a certain broadcast station with a receiver,we are actually

If the range of a $TV$ telecast is to be doubled,the height of the transmitting antenna must be: