If a $TV$ transmission antenna covers a radius of $128 \, km$,what should be the height of the antenna in $m$?

The wavelength of the carrier waves in a modern optical fiber communication network is close to ........ $nm$.

The modulation index used in amplitude modulation of a message signal of peak voltage $10 \,V$ is $0.5$. By how much should the peak voltage of the carrier signal be changed, so as to obtain the modulation index of $0.8$, keeping the peak voltage of the message signal the same as before?

$A$ 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

$A$ message signal of frequency $10 kHz$ is used to modulate a carrier wave of frequency $6 MHz$. The sideband frequencies 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