In the process of space communication,the use of a modem is necessary. In which one of the following modes does a modem act as a modulator and a demodulator respectively?

In satellite communication,the uplink frequency band used is

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

$A$ 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.

$A$ message signal of frequency $5\,kHz$ is used to modulate a carrier signal of frequency $2\,MHz$. The bandwidth for amplitude modulation is $..........\,kHz$.

$A$ $TV$ transmission tower antenna is at a height of $20\, m$. Suppose that the receiving antenna is at:
$(i)$ ground level
$(ii)$ a height of $5\, m$.
The increase in antenna range in case $(ii)$ relative to case $(i)$ is $n\%$.
The value of $n$,to the nearest integer,is .....$\%$