The transmission of $UHF$ range frequencies is done by.........

The characteristic impedance of a coaxial cable is of the order of .......... $\Omega$.

The height of a $TV$ tower is $150 \ m$. If the population density in the area covered by the $TV$ tower is $50 \ \text{lakhs}$, then the population density around the $TV$ tower is ....... $km^{-2}$. (Radius of the Earth is $6.4 \times 10^{6} \ m$)

An audio signal $v_{m} = 20 \sin(2 \pi \times 1500 t)$ amplitude modulates a carrier $v_{c} = 80 \sin(2 \pi \times 100,000 t)$. The value of percent modulation is..........

For $VHF$ signal broadcasting,what is the maximum service area in $km^{2}$ that will be covered by an antenna tower of height $30\, m$,if the receiving antenna is placed at the ground? Let the radius of the earth be $6400\, km$. (Round off to the nearest integer) (Take $\pi$ as $3.14$)

Mean optical power launched into an $8 \ km$ fibre is $120 \ \mu W$ and mean output power is $4 \ \mu W$,then the overall attenuation is ....... $dB$ (Given $\log 30 = 1.477$)