What is a common use of a Band Pass Filter in Radio Wave Propagation?

Question

What is a common use of a Band Pass Filter in Radio Wave Propagation?

1. A. It allows only a specific range of frequencies to pass through (Correct answer)
2. B. It allows all frequencies to pass through
3. C. It blocks all frequencies from passing through
4. D. It amplifies all frequencies equally

Correct Answer

Option A — It allows only a specific range of frequencies to pass through

Detailed Solution & Explanation

The correct answer is It allows only a specific range of frequencies to pass through.

Key Points

• A Band Pass Filter (BPF) passes frequencies lying between a lower and an upper cut-off, and attenuates everything outside that band.
• In radio wave propagation this selects the wanted channel while rejecting adjacent channels, image frequencies and out-of-band noise.
• A filter that passed all frequencies would be no filter at all, and one that blocked all frequencies would render the receiver useless.

Additional Information

• The four basic filter types are low pass, high pass, band pass and band stop (notch).
• The sharpness of a band pass filter is expressed by its quality factor, Q = f₀ / BW, where f₀ is the centre frequency and BW the bandwidth — a higher Q means a narrower, more selective passband.