The heights of the transmitting and receiving antennas are 33.8 m and 64.8 m respectively. The maximum distance between the antennas for satisfactory communication in line of sight mode is (radius of the earth $=6400 \mathrm{~km}$ )

Consider the following statements regarding digital signals

(i) provide a continuous set of values

(ii) represent values as discrete steps

(iii) can utilise binary system

(iv) are in the form of rectangular waves

Then the true statements are

An amplitude modulated wave is represented by $c_m(t)=10[1+0.6 \sin (1250 t)] \sin \left(10^8 t\right)$. Then modulation index is

A telephonic communication service is working at a carrier frequency of 20 GHz . Only $20 \%$ of it is utilised for transmission. If each channel requires a bandwidth of 5 kHz , then the number of telephonic channels that can be transmitted simultaneously are