$A$ signal of $100 \,THz$ frequency can be transmitted with maximum efficiency by

$A$ modulated signal is given by $C_m(t) = A_c \sin \omega_c t + \mu A_c \sin \omega_m t \sin \omega_c t$,where $\mu$ is the modulation index. To keep the signal without distortion,the value of $\mu$ should be

The function of a detector is to demodulate the modulated carrier wave and the steps for this process are

The intensity of a light pulse travelling along a communication channel decreases exponentially with distance $x$ according to the relation $I = I_0 e^{-\alpha x}$,where $I_0$ is the intensity at $x = 0$ and $\alpha$ is the attenuation constant. The attenuation in $dB/km$ for an optical fibre in which the intensity falls by $50$ percent over a distance of $50 \ km$ is

The characteristic impedance of a coaxial cable is typically in the range of ..........

$A$ transmitting antenna covers a range of $12.8 \ km$. Find the height of the antenna in $m$. (Radius of the Earth $= 6400 \ km$)