For a simple LC band-pass design around 14.2 MHz with a 100 kHz bandwidth, what is the approximate Q required?

• A. 14.2
• B. 142
• C. 1.42
• D. 0.142

Answer: (B)

Q is the measure of how selective a resonant circuit is, defined as the ratio of the center frequency to the bandwidth it passes. For a simple LC band-pass centered around 14.2 MHz with about 100 kHz bandwidth, the approximate Q is f0 divided by BW: 14.2 MHz / 0.1 MHz ≈ 142. A higher Q means a narrower passband, so this setup would require roughly 142. The other numbers would correspond to different bandwidths (for example, a Q of 14.2 would need a 1 MHz bandwidth, etc.), which don’t match the given 100 kHz.