Q 1. Consider an optical communication system operating at {tex} \lambda - 800 \mathrm { nm } {/tex}. Suppose, only {tex} 1 \% {/tex} of the optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting audio signals requiring a bandwidth of {tex} 8 \mathrm { kHz } {/tex}

Q 2. For sky wave propagation of a {tex} 10 \mathrm\ { MHz } {/tex} signal, what should be the minimum electron density in ionosphere

Q 3. In frequency modulation

Q 4. A wave is represented as \[ e = 10 \sin \left( 10 ^ { 8 } t + 6 \sin 1250 t \right) \] then the modulating index is

Q 5. A carrier is simultaneously modulated by two sine waves with modulation indices of 0.4 and {tex} 0.3 . {/tex} The resultant modulation index will be

Q 6. Long distance short-wave radio broadcasting uses

Q 7. A step index fibre has a relative refractive index of {tex} 0.88 \% . {/tex} What is the critical angle at the corecladding interface

Q 8. A sky wave with a frequency {tex} 55 \mathrm { MHz } {/tex} is incident on {tex} D {/tex} -region of earth's atmosphere at {tex} 45 . {/tex} The angle of refraction is (electron density for {tex} D {/tex} region is 400 electron/cm)

Q 9. Mean optical power launched into an 8 km fibre is {tex} 120 \mu W {/tex} and mean output power is {tex} 4 \mu W , {/tex} then the overall attenuation is (Given {tex} \log 30 = 1.477 ) {/tex}

Q 10. Maximum useable frequency (MUF) in F region layer is {tex} x , {/tex} when the critical frequency is {tex} 60 \mathrm { MHz } {/tex} and the angle of incidence is {tex} 70 ^ { \circ } . {/tex} Then {tex} x {/tex} is

Q 11. An amplitude modulated wave is modulated to {tex} 50 \% {/tex}. What is the saving in power if carrier as well as one of the side bands are suppressed

Q 12. In an FM system a 7 kHz signal modulates 108 MHz carrier so that frequency deviation is 50 kHz. The carrier swing is

Q 13. Through which mode of propagation, the radio waves can be sent
from one place to another

Q 14. In {tex} \mathrm { AM } {/tex}, the centpercent modulation is achieved when

Q 15. Range of frequencies allotted for commercial FM radio broadcast is

Q 16. An AM wave has 1800 watt of total power content, For {tex} 100 \% {/tex} modulation the carrier should have power content equal to

Q 17. Advantage of optical fibre

Q 18. The velocity factor of a transmission line {tex} x {/tex}. If dielectric constant of the medium is {tex} 2.6 , {/tex} the value of {tex} x {/tex} is

Q 19. The electron density of {tex} E , F , F {/tex} layers of ionosphere is {tex} 2 \times 10 ^{11},5 \times 10 ^ { n } {/tex}. and {tex} 8 \times 10 ^ { n} {/tex}. {tex} m ^{3} {/tex} respectively. What is the ratio of critical frequency for reflection of radiowaves

Q 20. In a diode AM-detector, the output circuit consist of {tex} R = 1k \Omega {/tex} and {tex} C = 10 {/tex} {tex} p F . {/tex} A carrier signal of {tex} 100 \mathrm { kHz } {/tex} is to be detected. Is it good

Q 21. The antenna current of an AM transmitter is {tex} 8 A {/tex} when only carrier is sent but increases to {tex} 8.96 A {/tex} when the carrier is sinusoidally modulated. The percentage modulation is

Q 22. The total power content of an AM wave is 900 {tex} W . {/tex} For {tex} 100 \% {/tex} modulation, the power transmitted by each side band is

Q 23. If {tex} \mu {/tex} and {tex} \mu_{1}{/tex} are the refractive indices of the materials of core and cladding of an optical fibre, then the loss of light due to its leakage
can be minimised by having

Q 24. In a radio receiver, the short wave and medium wave stations are tuned by using the same capacitor but coils of different inductance {tex} L_{s}{/tex} and {tex} L_{m}{/tex} respectively then

Q 25. The audio signal used to modulate {tex} 60 \sin \left( 2 \pi \times 10 \mathrm { t } \right) {/tex} is {tex} 15 \sin 300 \pi \mathrm { t } {/tex}. The depth of modulation is