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A pulse train has pulses \( 1 \ \mathrm{\mu s} \) wide. The bandwidth needed is roughly

  • A.250 kHz
  • B.500 kHz
  • C.1 MHz
  • D.2 MHz

Answer: B

The usual rule takes the bandwidth as the reciprocal of twice the pulse width:

\[ \begin{aligned} B \approx \frac{1}{2\tau} &= \frac{1}{2 \times 10^{-6}} \\ &= 500 \ \mathrm{kHz} \end{aligned} \]

so about 500 kHz. One megahertz is the reciprocal of the width alone, a more conservative figure some texts prefer. The other values follow from a factor of four either way. Narrow pulses demand wide channels, which is the resource every pulse scheme spends and the reason bandwidth rather than power usually limits them.

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