$A$ radio can tune to any station in the $6\,MHz$ to $10\,MHz$ band. The value of the corresponding wavelength bandwidth will be $....\,m$.

Statement-$1$: Sky wave signals are used for long-distance radio communication.
Statement-$2$: These signals are generally less stable than ground wave signals.

An $FM$ broadcast transmitter,using a modulating signal of frequency $20\,kHz$,has a deviation ratio of $10$. The bandwidth required for transmission is $.......kHz$.

An audio signal $v_{m} = 20 \sin(2 \pi \times 1500 t)$ amplitude modulates a carrier $v_{c} = 80 \sin(2 \pi \times 100,000 t)$. The value of percent modulation is..........

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	$IV$. $65-75 \ km$

For sky wave propagation of a $10\, MHz$ signal, what should be the minimum electron density in the ionosphere?