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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 7
46.
Three point tracking is achieved with
double conversion
padder capacitor
double spotting
variable selectivity
Answer: Option
Explanation:

To obtain three point tracking a capacitor is connected in series with local oscillator coil. This capacitor is called padder capacitor.

47.
In TV transmitter, visual exciter may consist of
  1. Video processing unit
  2. Visual modulator
  3. VSB filter
  4. Delay equaliser
  5. Frequency converter
Which of the above are actually a part of visual exciter?
1, 2 and 3
2, 3 and 4
1, 2, 3 and 4
1, 2, 3, 4 and 5
Answer: Option
Explanation:

All these are part of visual exciter.

48.
The positive peak of an AM wave is 16 V and the minimum value is 4 V Assuming single tone modulation, the modulation index is
0.6
0.25
4
0.36
Answer: Option
Explanation:

Average value = 10 V and .

49.
In a circuit the value of resistor is made four times. The noise voltage generated by this resistance will
be doubled
be increased four times
remain the same
become half
Answer: Option
Explanation:

Noise voltage ∝ R.

50.
A resistor of 10 kΩ has an rms noise voltage of 1 mV under a certain set of conditions. A resistor of 20 kΩ under the same conditions will have an rms noise voltage of
1 mV
2 mV
1.414 mV
4 mV
Answer: Option
Explanation:

i ∝ R.

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