The process of superimposing a signal frequency onto a carrier wave is known as .......

$A$ transmitting antenna has a height of $20 \,m$. What will be the height of the receiving antenna if the maximum distance between them for satisfactory communication in line-of-sight $(LOS)$ mode is $40 \,km$ (in $\,m$)? (The radius of the Earth is $6400 \,km$.)

The heights of transmitting and receiving antennas are respectively $\frac{1}{20000}$ and $\frac{1}{80000}$ times the radius of the earth. The maximum distance between these two antennas for satisfactory communication in line of sight mode is (Radius of the earth $= 6.4 \times 10^6 \ m$) (in $km$)

$A$ diode detector is used to detect an amplitude modulated wave with $60\%$ modulation,using a capacitor of $250 \ pF$ in parallel with a resistor of $100 \ k\Omega$. What is the maximum modulation frequency that can be detected by this circuit?

An oscillator is producing $FM$ waves of frequency $2 \text{ kHz}$ with a frequency variation of $10 \text{ kHz}$. What is the modulation index?

In $TV$ transmission,the audio signal is ........ modulated and the video signal is ........ modulated.