What is bandwidth?

Question

What is bandwidth?

Answer 1

Bandwidth is usually a function of how a particular carrier frequency is modulated.  The center carrier frequency is usually assigned a bandwidth based upon the amount of deviation from the carrier center frequency created by modulation signal strength and/or change in modulation frequency or phase. The signal bandwidth is usually defined as +/- 3dB points either side of the carrier center frequency.

For example, a broadcast station might have a carrier frequency of 1.0 MHz and a +/- 3dB bandwidth of 10 KHz. That would be 1.0 MHz + 5 KHz (1.005 MHz), and 1.0 MHz - 5 KHz (0.995 MHz).

The + 5 KHz deviation would be considered the USB (upper side band),

and the - 5 KHz deviation would be the LSB (lower side band).

+/- 3 dB bandwidth points simply means that is where the USB and LSB signal strength is down by 0.707 the carrier strength, or the half power points.

Answer 2

It depends if you are talking about digital (e.g. computer) or analogue (e.g. FM radio) signals.

In the digital world, the term bandwidth is used to define the amount of  information (data) that you can get through a communications mean (e.g. a cable, a wireless connection, etc).  Think of it as the size of the pipe used to transmit that information.  The more bandwidth, the more data you can get through in a given time frame (e.g. 5 Megabytes per second)

In the analogue world, somebody else has posted an answer that gives you a very correct and technical definition of bandwidth in that context.