Coaxial cable,a widely used wire medium,offers an approximate frequency bandwidth of:

The waves which are reflected back to the earth by the ionosphere are:

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	$IV$. $65-75 \ km$

What is the frequency range of signals that can be transmitted using a $Twisted\, pair\, wire$?

$A$ baseband signal of $3.5\, MHz$ frequency is modulated with a carrier signal of $3.5\, GHz$ frequency using amplitude modulation. What should be the minimum size of antenna required to transmit the modulated signal?

In communication with the help of an antenna,if the height is doubled,then the range covered,which was initially $r$,would become: