For an amplitude modulated wave,the maximum and minimum amplitudes are $12 \,V$ and $3 \,V$ respectively. Then the modulation index is

What is the bit rate in $bits/sec$ for a signal with $16$ quantization levels and a sampling rate of $8 \, kHz$?

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

An $FM$ broadcast transmitter,using a modulating signal of frequency $20\,kHz$,has a deviation ratio of $10$. The bandwidth required for transmission is $.......kHz$.

The electron density of $E, F_1, F_2$ layers of the ionosphere is $2 \times 10^{11} \, m^{-3}$,$5 \times 10^{11} \, m^{-3}$,and $8 \times 10^{11} \, m^{-3}$ respectively. What is the ratio of critical frequencies for the reflection of radio waves?

If the range of a $TV$ telecast is to be doubled,the height of the transmitting antenna must be: