Radio waves that reach the receiver after being reflected from the ionosphere propagate via .......

The height of a transmission antenna is $100 \, m$. The population density is $1000 \, \text{people}/km^2$. How many people can watch the program?

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

$A$ carrier wave of peak voltage $15 \,V$ is used to transmit a message signal. If the modulation index is $60 \%$, then the peak voltage of the modulating signal is (in $\,V$)

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

$A$ receiving station on the ground is receiving a signal of frequency $5 \ MHz$ from a transmitter. Then the signal can come via