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

The total maximum transmitted power in amplitude modulation if the carrier output power is $1 \ kW$ is

Mean optical power launched into an $8 \ km$ fibre is $120 \ \mu W$ and mean output power is $4 \ \mu W$,then the overall attenuation is ....... $dB$ (Given $\log 30 = 1.477$)

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?

$A$ signal of $0.1 \, kW$ is transmitted in a cable. The attenuation of the cable is $-5 \, dB$ per $km$ and the cable length is $20 \, km$. The power received at the receiver is $10^{-x} \, W$. The value of $x$ is ....... .
$[\text{Gain in } dB = 10 \log_{10}(\frac{P_0}{P_i})]$

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