If the area covered by an $FM$ radio station is to be tripled,the height of the antenna must be .......

The digital signals are used for transmission in communication systems. They are

The bandwidth of an optical fiber is

For short-distance communication,waves with a frequency of $f$ $MHz$ are reflected back from the ionosphere. If the electron density of the ionosphere is $10^{11} \ m^{-3}$,what is the value of $f$?

$A$ carrier wave $v_{c}(t) = 160 \sin(2 \pi \times 10^{6} t) \text{ V}$ is made to vary between $V_{\max} = 200 \text{ V}$ and $V_{\min} = 120 \text{ V}$ by a message signal $v_{m}(t) = A_{m} \sin(2 \pi \times 10^{3} t) \text{ V}$. The peak voltage $A_{m}$ of the modulating signal is ..... .

Given below are two statements
Statement $I:$ For transmitting a signal,the size of the antenna $(l)$ should be comparable to the wavelength of the signal (at least $l = \frac{\lambda}{4}$ in dimension).
Statement $II:$ In amplitude modulation,the amplitude of the carrier wave remains constant (unchanged).
In the light of the above statements,choose the most appropriate answer from the options given below.