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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 7
16.

Assertion (A): EM waves are attenuated as they travel outward from a source

Reason (R): Both field intensity and power density follow inverse square law.

Both A and R are correct and R is correct explanation of A
Both A and R are correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
Answer: Option
Explanation:

As per inverse square law, power is inversely proportional to square of distance.

17.
The frequency response of a microphone means
bandwidth of frequencies having output with in ± 1 dB of the output at 1000 Hz
bandwidth of frequencies having output with in ± 3 dB of the output at 1000 Hz
bandwidth of frequencies having output with in ± 1 dB of the output at 500 Hz
bandwidth of frequencies having output with in ± 3 dB of the output at 500 Hz
Answer: Option
Explanation:

100 Hz is taken as standard for specifying the output.

18.
Graphic equaliser system in stereophonic systems generally have
3 or 4 bands
1 band
more than 8 bands
large number of bands
Answer: Option
Explanation:

Stereo systems have 3 or 4 bands at 300 Hz, 1000 Hz, 10000 Hz etc. in graphic equaliser system.

19.
An amplifier operating over a frequency range of 18 to 20 MHz has 10 kΩ input resistance. At a temperature of 27° C, the noise voltage at input of amplifier is (Boltzman constant k = 1.38 x 10-23 J/K)
18.2 μV
182 μV
16.2 μV
162 μV
Answer: Option
Explanation:

Using Equation Va = (4 x 1.38 x 10-23 x 300 x 2 x 106 x 104)0.5 = 18.2 x 10-6 V.

20.
Some sources of TV programs are
  1. TV camera
  2. Telecine
  3. VTR
  4. External signal
Which of the above are actually present in a TV studio?
1, 2, 3 and 4
1, 2, 3
1 and 3
1 2 and 4
Answer: Option
Explanation:

All these are present.

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