# Online Electronics and Communication Engineering Test - Communication Systems Test 3 Loading Test...

Instruction:

• This is a FREE online test. DO NOT pay money to anyone to attend this test.
• Total number of questions : 20.
• Time alloted : 30 minutes.
• Each question carry 1 mark, no negative marks.
• DO NOT refresh the page.
• All the best :-).

1.

In CCIR-B system, the time between start of one H syn. pulse and next is

A.
 64 μs B.
 6.4 μs C.
 640 μs D.
 0.64 μs Explanation:

The frequency of H pulses is 15625 Hz.

Hence .

2.

In a CD player the speed of CD is

A.
 constant at 500 rpm B.
 constant at 200 rpm C.
 varies from 200 to 500 rpm D.
 none of the above Explanation:

Since the circumference of outer tracks is more than that of tracks near the centre, the speed of disc is varied from 200 rpm to 500 rpm.

3.

In a 100% amplitude modulated signal, the power in the upper sideband when carrier power is to be 100 W and modulation system SSBSC, is

A.
 100 W B.
 66 W C.
 50 W D.
 25 W Explanation:

Modulation index = 100% 1

Pc = 100 W 4.

Trinitron is a monochrome picture tube.

A.
 True B.
 False Explanation:

Frequency band for local programs is fixed.

5.

Two sinusoidal signals of same amplitude and frequencies 10 kHz and 10.1 kHz are added together. The combined signal is given to an ideal frequency detector. The output of the detector is

A.
 0.1 kHz sinusoidal B.
 10.1 kHz sinusoidal C.
 a linear function D.
 a constant Explanation:

Y(t) = A cos (2p x 104 t) + A cos (2p x 10.1 x 103 t)

when passed through high pass filter,

Output will be A cos (2p x 10.1 x 103 t) only.

6.

In cellular telephone each cell is designed to handle

A.
 45 two way communications B.
 90 two way communications C.
 45 one way communications D.
 180 two way communications Explanation:

Each cell is designed for 45 two way conversations.

7.

Which is a digital coding technique?

A.
 PCM B.
 DM C.
 DPCM D.
 All 8.

The IF frequencies in a TV receiver

A.
 38.9 MHz for video and 33.4 MHz for audio B.
 38.9 MHz for both video and audio C.
 33.4 MHz for both video and audio D.
 33.4 MHz for video and 38.9 MHz for audio 9.

In FDM systems used for telephone, which modulation scheme is adopted?

A.
 AM B.
 DSB-SC C.
 SSB-SC D.
 FM 10.

Noise can be reduced by increasing sampling rate

A.
 true B.
 false C.
 can't say D.
 insufficient data 11.

In cell communication, cell stands for

A.
 Geographical Area B.
 Battery C.
 Location D.
 No meaning 12.

If the circumference of a spherical target is between 1 to 10 wavelength in a radar system, the situation is called

A.
 resonance region B.
 Rayleigh region C.
 optical region D.
 binomial region 13.

Square law modulators utilise

A.
 linear range of V-I characteristics of a diode B.
 linear range of V-I characteristics of a triode C.
 non-linear region of V-I dynamic characteristics of a diode D.
 non-linear region of V-I dynamic characteristics of a triode 14.

The maximum permissible distance between two samples of a 10 kHz signal

A.
 100 μ sec B.
 50 μ sec C.
 10 μ sec D.
 none 15.

In AM the amplitude of carrier components ... while in FM it

A.
 remains constant, does not remain constant B.
 does not remain constant ... remains constant C.
 remains constant... also remains constant D.
 does not remain constant, also does not remain constant 16.

If carrier modulated by a digital bit stream had one of the possible phases of 0°, 90°, 180°, 270°, then the modulation is called.

A.
 BPSK B.
 QPSK C.
 QAM D.
 MSK 17.

If F(ω) is Fourier transform of f(t), then Fourier transform of f(t) cos2 ωct is

A. F(ω) + [F(ω + 2ωc) + F(ω - 2ωc)] B.
 F(ω) + [F(ω + 2ωc) + F(ω - 2ωc)] C.
 F(ω) - [F(ω + 2ωc) + F(ω - 2ωc)] D. F(ω) - [F(ω + 2ωc) + F(ω - 2ωc)] 18.

The currents fed to the two dipoles of turnstile antenna are

A.
 in phase B.
 in quadrature C.
 in phase opposition D.
 either (a) or (c) 19.

Consider the following statements as regards BPSK and QPSK:

1. In BPSK we deal individually with each bit of duration Tb
2. In QPSK we lump two bits to form a symbol
3. In both BPSK and QPSK signal changes occur at bit rate
4. In QPSK the symbol can have any one of four possible values
Which of the above statements are correct?

A.
 1, 2, 3, 4 B.
 1, 2, 3 C.
 1, 2, 4 D.
 2, 3, 4 20.

A pre-emphasis circuit provides extra noise immunity by

A.
 converting the phase modulation to frequency modulation B.
 pre-amplifying the whole audio band C.
 boosting the base frequencies D.
 amplifying the higher audio frequencies 