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

If the highest modulating frequency of the wave is $5 kHz$,then the number of stations that can be accommodated in a $150 kHz$ bandwidth is

The minimum size of an antenna for transmitting electromagnetic waves at $1500 \text{ MHz}$ is

The refractive index of the ionosphere:

In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having an electron density of $10^{11} \text{ per } m^3$ (in $\text{ MHz}$)?

The maximum amplitude for an amplitude modulated wave is found to be $12\, V$ while the minimum amplitude is found to be $3\, V$. The modulation index is $0.6\, x$ where $x$ is $....$