Communication Systems · Physics · JEE Main

To radiate EM signal of wavelength $$\lambda$$ with high efficiency, the antennas should have a minimum size equal to:

Match List - I with List - II

Choose the correct answer from the options given below:

The amplitude of $$15 \sin (1000 \pi \mathrm{t})$$ is modulated by $$10 \sin (4 \pi \mathrm{t})$$ signal. The amplitude modulated signal contains frequencies of

A. $$500 \mathrm{~Hz}$$

B. $$2 \mathrm{~Hz}$$

C. $$250 \mathrm{~Hz}$$

D. $$498 \mathrm{~Hz}$$

E. $$502 \mathrm{~Hz}$$

Choose the correct answer from the options given below:

In satellite communication, the uplink frequency band used is :

A transmitting antenna is kept on the surface of the earth. The minimum height of receiving antenna required to receive the signal in line of sight at $$4 \mathrm{~km}$$ distance from it is $$x \times 10^{-2} \mathrm{~m}$$. The value of $$x$$ is __________.

(Let, radius of earth $$\mathrm{R}=6400 \mathrm{~km}$$ )

A message signal of frequency $$3 ~\mathrm{kHz}$$ is used to modulate a carrier signal of frequency $$1.5 ~\mathrm{MHz}$$. The bandwidth of the amplitude modulated wave is

A carrier wave of amplitude 15 V is modulated by a sinusoidal base band signal of magnitude 3 V. The ratio of maximum amplitude to minimum amplitude in an amplitude modulated wave is

The power radiated from a linear antenna of length $$l$$ is proportional to

(Given, $$\lambda=$$ Wavelength of wave):

A TV transmitting antenna is $$98 \mathrm{~m}$$ high and the receiving antenna is at the ground level. If the radius of the earth is $$6400 \mathrm{~km}$$, the surface area covered by the transmitting antenna is approximately:

For an amplitude modulated wave the minimum amplitude is $$3 \mathrm{~V}$$, while the modulation index is $$60 \%$$. The maximum amplitude of the modulated wave is:

By what percentage will the transmission range of a TV tower be affected when the height of the tower is increased by $$21 \%$$ ?

In an amplitude modulation, a modulating signal having amplitude of X Volt is superimposed with a carrier signal of amplitude Y Volt in first case. Then, in second case, the same modulating signal is superimposed with different carrier signal of amplitude 2Y Volt. The ratio of modulation index in the two cases respectively will be :

Which of the following frequencies does not belong to FM broadcast ?

Given below are two statements :

Statement I : For transmitting a signal, size of antenna ( $l$ ) should be comparable to wavelength of signal (at least $l=\frac{\lambda}{4}$ in dimension)

Statement II: In amplitude modulation, amplitude of carrier wave remains constant (unchanged).

In the light of the above statements, choose the most appropriate answer from the options given below

The amplitude of $$15 \sin (1000 \pi \mathrm{t})$$ is modulated by $$10 \sin (4 \pi \mathrm{t})$$ signal. The amplitude modulated signal contains frequency (ies) of

A. $$500 \mathrm{~Hz}$$

B. $$2 \mathrm{~Hz}$$

C. $$250 \mathrm{~Hz}$$

D. $$498 \mathrm{~Hz}$$

E. $$502 \mathrm{~Hz}$$

Choose the correct answer from the options given below:

Choose the correct answer from the options given below:

A sinusoidal carrier voltage is amplitude modulated. The resultant amplitude modulated wave has maximum and minimum amplitude of $$120 \mathrm{~V}$$ and $$80 \mathrm{~V}$$ respectively. The amplitude of each sideband is :

The modulation index for an A.M. wave having maximum and minimum peak-to-peak voltages of 14 mV and 6 mV respectively is-

If the height of transmitting and receiving antennas are 80 m each, the maximum line of sight distance will be:

Given : Earth's radius $$=6.4\times10^6$$ m

Match List I with List II

Choose the correct answer from the options given below :

A message signal of frequency 5 kHz is used to modulate a carrier signal of frequency 2 MHz. The bandwidth for amplitude modulation is :

Match List I with List II

Choose the correct answer from the options given below :

A modulating signal is a square wave, as shown in the figure.

If the carrier wave is given as $$\mathrm{c(t) = 2\sin(8\pi t)}$$ volts, the modulation index is :

Find the modulation index of an AM wave having $$8 \mathrm{~V}$$ variation where maximum amplitude of the AM wave is $$9 \mathrm{~V}$$.

A FM Broadcast transmitter, using modulating signal of frequency 20 kHz has a deviation ratio of 10. The Bandwidth required for transmission is :

In the case of amplitude modulation to avoid distortion the modulation index $$(\mu)$$ should be :

A square wave of the modulating signal is shown in the figure. The carrier wave is given by $$C(t)=5 \sin (8 \pi t)$$ Volt. The modulation index is :

At a particular station, the TV transmission tower has a height of 100 m. To triple its coverage range, height of the tower should be increased to

The maximum and minimum voltage of an amplitude modulated signal are $$60 \mathrm{~V}$$ and $$20 \mathrm{~V}$$ respectively. The percentage modulation index will be :

A radio can tune to any station in $$6 \,\mathrm{MHz}$$ to $$10 \,\mathrm{MHz}$$ band. The value of corresponding wavelength bandwidth will be :

In AM modulation, a signal is modulated on a carrier wave such that maximum and minimum amplitudes are found to be 6 V and 2 V respectively. The modulation index is :

A speech signal given by 11 sin(2200 $$\pi$$t) V is used for amplitude modulation with a carrier signal given by 44 sin(6600 $$\pi$$t) V. The minimum amplitude of modulated wave will be :

The TV transmission tower at a particular station has a height of 125 m. For doubling the coverage of its range, the height of the tower should be increased by

Only 2% of the optical source frequency is the available channel bandwidth for an optical communicating system operating at 1000 nm. If an audio signal requires a bandwidth of 8 kHz, how many channels can be accommodated for transmission :

Amplitude modulated wave is represented by $${V_{AM}} = 10\,[1 + 0.4\cos (2\pi \times {10^4}t)]\cos (2\pi \times {10^7}t)$$. The total bandwidth of the amplitude modulated wave is :

Match List-I with List-II

We do not transmit low frequency signal to long distances because-

(a) The size of the antenna should be comparable to signal wavelength which is unreal solution for a signal of longer wavelength.

(b) Effective power radiated by a long wavelength baseband signal would be high.

(c) We want to avoid mixing up signals transmitted by different transmitter simultaneously.

(d) Low frequency signal can be sent to long distances by superimposing with a high frequency wave as well.

Therefore, the most suitable option will be :

A sinusoidal wave y(t) = 40sin(10 $$\times$$ 10⁶ $$\pi$$t) is amplitude modulated by another sinusoidal wave x(t) = 20sin (1000 $$\pi$$t). The amplitude of minimum frequency component of modulated signal is :

Choose the correct statement for amplitude modulation :

Match List I with List II

Choose the correct answer from the following options:

A signal of 100 THz frequency can be transmitted with maximum efficiency by :

A baseband signal of 3.5 MHz frequency is modulated with a carrier signal of 3.5 GHz frequency using amplitude modulation method. What should be the minimum size of antenna required to transmit the modulated signal?

A modulating signal $$2 \sin \left(6.28 \times 10^{6}\right) t$$ is added to the carrier signal $$4 \sin \left(12.56 \times 10^{9}\right) t$$ for amplitude modulation. The combined signal is passed through a non-linear square law device. The output is then passed through a band pass filter. The bandwidth of the output signal of band pass filter will be _________ $$\mathrm{MHz}$$.

The required height of a TV tower which can cover the population of $$6.03$$ lakh is $$h$$. If the average population density is 100 per square $$\mathrm{km}$$ and the radius of earth is $$6400 \mathrm{~km}$$, then the value of $$h$$ will be _____________ $$m$$.

The height of a transmitting antenna at the top of a tower is 25 m and that of receiving antenna is, 49 m. The maximum distance between them, for satisfactory communication in LOS (Line-Of-Sight) is K$$\sqrt5$$ $$\times$$ 10² m. The value of K is ___________.

(Assume radius of Earth is 64 $$\times$$ 10⁺⁵ m) [Calculate upto nearest integer value]

An antenna is placed in a dielectric medium of dielectric constant 6.25. If the maximum size of that antenna is 5.0 mm, it can radiate a signal of minimum frequency of __________ GHz.

(Given $$\mu$$_r = 1 for dielectric medium)