Why crystal receiver has poor selectivity?

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RRB ALP Mechanic Radio & TV 23 Jan 2019 Official Paper (Shift 3)
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  1. No loud speaker is used
  2. No battery is used
  3. it has long antenna
  4. No tuned circuit is used

Answer (Detailed Solution Below)

Option 4 : No tuned circuit is used
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The correct option is 4

Concept:

The selectivity of a radio receiver is its ability to select a particular signal station and reject others in the frequency spectrum.

  • A crystal radio receiver, or crystal set, is a very simple radio receiver, popular in the early days of radio. It needs no other power source but that received from radio waves by an antenna.
  • It uses a crystal detector (composed of a piezoelectric crystal such as galena) to demodulate the signal.
  • In a crystal receiver, there oftentimes isn't a clear, defined "tuned circuit." A tuned circuit (like an LC circuit) allows for specific frequencies to be selected and others to be rejected, improving the selectivity of the receiver.

The other options:

1) No loudspeaker is used: This might affect the volume or audibility but not the selectivity.
2) No battery is used: The absence of batteries is a defining feature of crystal radios, but this doesn't directly impact their selectivity.
3) It has a long antenna: The length of the antenna can affect reception, but doesn't directly correlate to the selectivity of the receiver.

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