The process of superimposing low-frequency signals onto high-frequency carrier waves is called ..........

The ionosphere acts as a reflector for which frequency range?

The maximum distance up to which $TV$ transmission from a $TV$ tower of height $h$ can be received is proportional to

$A$ wave is represented as $e = 10\,(1 + 6\, \sin(50t)) \sin(10^8t)$. The modulation index is:

$A$ 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?

$A$ ground receiver station is receiving a signal at $5\, MHz$ transmitted from a ground transmitter at a height of $300\, m$,located at a distance of $100\, km$ from the receiver station. Given: Radius of Earth $R = 6.4 \times 10^6\, m$,$N_{\max}$ of ionosphere = $10^{12}\, m^{-3}$. Identify the mode of propagation.