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Q 1. Buffer amplifier is used at the transmitting end to
feed carrier frequency to master oscillator
amplify carrier frequency
mix modulating signal with carrier frequency
isolate master oscillator from other stages of transmitter.
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Q 2. An AM- signal is given as
{tex}X_\mathrm {AM} (t) = 100 [p(t) + 0.5g(t)]cos \omega_c t{/tex} in interval {tex} 0\leq t\leq 1 {/tex}. One set of possible values of the modulating signal and modulation index would be
{tex} t , 0.5 {/tex}
{tex} t , 1.0 {/tex}
{tex} t , 1.5 {/tex}
{tex} t ^ { 2 } , 2.0 {/tex}
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Q 3. The antenna current of an AM transmitter is 8 when only the carrier is sent, but it increases to 8.93 when the carrier is modulated by a single sine wave. Find the percentage modulation.
{tex} 60.1 \% {/tex}
{tex} 70.1 \% {/tex}
{tex} 80.1 \% {/tex}
{tex} 50.1 \% {/tex}
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Q 4. In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be
{tex}50{/tex} cycles/s
{tex}100{/tex} cycles/s
{tex}500{/tex} cycles/s
{tex} 50,000 {/tex} cycles/s
In this modulation, the audio frequency wave is superimposed on a high frequency carrier wave in a manner that the frequency of modulated wave is 100 times as that of the carrier wave, but its amplitude is made proportional to the instantaneous amplitude of the audio frequency wave. Thus, the appropriate carrier frequency will be 50000 cycles/second
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Q 5. Communication is the process of
keeping in touch
exchange information
broad casting
entertainment by electronics
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Q 6. Which of the following is the element of a communication system?
Transmitter
channel
Receiver
All of the above
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Q 7. A transducer used at the transmitting end, serves the purpose of converting
electrical signal to sound form
sound signal to electrical form
electrical signal to magnetic form
sound signal to magnetic form
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Q 8. The term channel is used to indicate
the amplitude range allocated to a given source
the frequency range allocated to a given source
the voltage-range allocated to a given source
All of the above
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Q 9. The purpose of a detector at the receiving end is
to amplify signal
to reduce its frequency level
to modulate signal
to demodulate signal
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Q 10. As the height of the satellite, orbit gets lower, the speed of the satellite
increases
decreases
remain same
both (a) and (b)
With decrease in 'r' velocity of satellite increases
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Q 11. A {tex} 1 \mathrm { kW } {/tex} carrier is modulated to a depth of {tex} 80 \% . {/tex} The total power in the modulated wave is
1.32
1.56
1.84
1.96
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Q 12. If the heights of transmitting and the receiving antennas are each equal to {tex} h , {/tex} the maximum line-of-sight distance between them is (R is the radius of earth)
{tex} \sqrt { 2 \mathrm { Rh } } {/tex}
{tex} \sqrt { 4 \mathrm { Rh } } {/tex}
{tex} \sqrt { 6 \mathrm { R } h } {/tex}
{tex} \sqrt { 8 \mathrm { R } h } {/tex}
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Q 13. For sky wave propagation of a {tex} 10 \mathrm { MHz } {/tex} signal, what should be the minimum electron density in ionosphere
{tex} \sim 1.2 \times 10 ^ { 12 } \mathrm { m } ^ { - 3 } {/tex}
{tex} \sim 10 ^ { 6 } m ^ { - 3 } {/tex}
{tex} \sim 10 ^ { 14 } \mathrm { m } ^ { - 3 } {/tex}
{tex} \sim 10 ^ { 22 } \mathrm { m } ^ { - 3 } {/tex}
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Q 14. The electron density of a layer of ionosphere at a height {tex} 150 \mathrm { km } {/tex} from the earth's surface is {tex} 9 \times 10 ^ { 9 } {/tex} per {tex} \mathrm { m } ^ { 3 } . {/tex} For the sky transmission from this layer up to a range of {tex} 250 \mathrm { km } {/tex}, The critical frequency of the layer is
{tex} 2 \ \mathrm { Hz } {/tex}
{tex} 2.7\ \mathrm { Hz } {/tex}
{tex} 2.78\ \mathrm { kHz } {/tex}
{tex} 2.7 \ \mathrm { MHz } {/tex}
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Q 15. Calculate the power developed by an amplitude modulated wave in a load resistance of {tex} 100 \Omega , {/tex} if the peak voltage of carrier wave is {tex} 100 \mathrm { V } {/tex} and modulation index is {tex} 0.4 . {/tex}
{tex} 50 \ \mathrm { watt } {/tex}
{tex} 54\ \mathrm { watt } {/tex}
{tex} 104 \ \mathrm { watt } {/tex}
{tex} 4 \ \mathrm { watt } {/tex}
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Q 16. In an FM system a {tex} 7 \mathrm { kHz } {/tex} signal modulates {tex} 108 \mathrm { MHz } {/tex} carrier so that frequency deviation is {tex} 50 \mathrm { kHz } {/tex}. The carrier swing is
{tex}7.1{/tex}
{tex}2.8{/tex}
{tex}5.8{/tex}
{tex}3.2{/tex}
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Q 17. If {tex} \mathrm { E } _ { \mathrm { c } } = 20 \sin 10 ^ { 5 } \pi \mathrm { t } {/tex} and {tex} \mathrm { E } _ { \mathrm { m } } = 10 \sin 400 \pi \mathrm { t } {/tex} are carrier and modulating signals, the modulation index is:
{tex} 56 \% {/tex}
{tex} 30 \% {/tex}
{tex} 50 \% {/tex}
{tex} 48 \% {/tex}
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Q 18. A tuned amplifier circuit is used to generate a carrier frequecy of {tex} 2 \mathrm { MHz } {/tex} for the amplitude modulation. The value of {tex} \sqrt { \mathrm { LC } } {/tex} is:
{tex} \frac { 1 } { 3 \pi \times 10 ^ { 6 } } {/tex}
{tex} \frac { 1 } { 2 \pi \times 10 ^ { 6 } } {/tex}
{tex} \frac { 1 } { 4 \pi \times 10 ^ { 6 } } {/tex}
{tex} \frac { 1 } { 2 \times 10 ^ { 6 } } {/tex}
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Q 19. The maximum range for the tropospheric transmission of radio wave of wavelength {tex} 3 \mathrm { m } {/tex} using the transmitting antenna and receiving antenna of hights {tex} 100 \mathrm { m } {/tex} and {tex} 60 \mathrm { m } {/tex} respectively is
{tex} 8 \mathrm { m } {/tex}
{tex} 800 \mathrm { m } {/tex}
{tex} \mathrm { 8km } {/tex}
{tex} 80 \mathrm { km } {/tex}
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Q 20. The velocity of all radio waves in free space is {tex} 3 \times 10 ^ { 8 } \mathrm { m } / \mathrm { s } {/tex}. What is the frequency of a radio wave of wavelength {tex} 150 \mathrm { m } {/tex}.
{tex} 5 \ \mathrm { MHz } {/tex}
{tex} 2 \ \mathrm { MHz } {/tex}
{tex} 0.5 \ \mathrm { MHz } {/tex}
{tex} 0 \ \mathrm { MH z}{/tex}
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Q 21. Determine the modulation index {tex} \left( \mathrm { m } _ { \mathrm { f } } \right) {/tex} and carrier swing {tex}\mathrm {(S)}{/tex} of an {tex} \mathrm { FM } {/tex} carrier having a frequency deviation of {tex} 25 \mathrm { kHz } {/tex} and a modulating signal of {tex} 5 \mathrm { kHz } {/tex}.
{tex} m _ { f } = 3 {/tex}
{tex} m _ { f } = 5 {/tex}
{tex} m _ { f } = 8 {/tex}
{tex} m _ { f } = 9 {/tex}
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Q 22. {tex} 1000 \mathrm { KHz } {/tex} carrier wave is amplitude modulated by the signal frequency {tex} 200 - 4000 \mathrm { Hz } {/tex}. The channel width of this case is:
{tex} 8 \ \mathrm { KHz } {/tex}
{tex} 4 \ \mathrm { KHz } {/tex}
{tex} 7.6 \ \mathrm { KHz } {/tex}
{tex} 3.8 \ \mathrm { KHz } {/tex}
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Q 23. Maximum usable 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 calculate {tex} x . {/tex}
{tex} 122 \mathrm { MHz } {/tex}
{tex} 216 \mathrm { Hz } {/tex}
{tex} 175 \mathrm { MHz } {/tex}
{tex} 75 \mathrm { H z} {/tex}
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Q 24. A carrier frequency of {tex} 1 \mathrm { MHz } {/tex} and peak value of {tex} 10 \mathrm { V } {/tex} is amplitude modulated with a signal frequency of {tex} 10 \mathrm { kHz } {/tex} with peak value of {tex} 0.5 \mathrm { V } {/tex}. Then, the modulation index and the side band frequencies respectively are
{tex}0.05{/tex} and {tex} 1 \pm 0.010 \ \mathrm { MHz } {/tex}
{tex}0.5{/tex} and {tex} 1 \pm 0.010 \ \mathrm { MHz } {/tex}
{tex}0.5{/tex} and {tex} 1 \pm 0.005 \ \mathrm { MHz } {/tex}
{tex}0.05{/tex} and {tex} 1 \pm 0.005\ \mathrm { MHz } {/tex}
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Q 25. A {tex} 10 \mathrm { kW } {/tex} transmitter emits radio waves of wavelength {tex}500 \mathrm { m } . {/tex} The number of photons emitted per second by the transmitter is of the order of
{tex} 10 ^ { 37 } {/tex}
{tex} 10 ^ { 31 } {/tex}
{tex} 10 ^ { 25 } {/tex}
{tex} 10 ^ { 43 } {/tex}
