How to Convert Pulse Width to Bandwidth

Connect the signal to the fast oscilloscope. Connect the signal trigger to the trigger input of the oscilloscope. Adjust the trigger timing to capture a single pulse from the signal in the center of the measurement range.

Adjust the time base of the oscilloscope to make the width of the signal trace large enough to measure conveniently and accurately. As you adjust the time base, you may also have to adjust the trigger timing to keep the pulse trace in a convenient location.

Measure the width of the pulse at half its maximum voltage. This value, abbreviated as FWHM, is a common measure of pulse width. Your oscilloscope may have adjustable markers to help you make this measurement accurately, but you can also do it ̶0;by hand̶1; by examining the trace on the oscilloscope.

Convert the width to a time by multiplying the measurement in Step 3 by the time base of the oscilloscope. For example, if the time base is 50 microseconds per division, and the measured width is 3.74 divisions, the pulse width is 187 microseconds.

Convert the time to a bandwidth. To communicate, a system must turn on and off, so the time of a single pulse is half the time needed for the system to communicate. Time is the inverse of frequency, so the maximum bandwidth frequency is:
BW = 1 / (2 x pulse width).
For the example given, the bandwidth is
BW = 1 / (374 microseconds) = 2674 Hz.

Repeat the measurement several times and average the readings. The average reading represents the bandwidth of the system.