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# What is this half power point? And why is it called like that? watch

1. What is this half power point and half power frequency?

Also, what is the difference between frequency range and bandwidth?

From what I understand, bandwidth is the difference between the max frequency and min frequency, while the frequency range is described as "min frequency to max frequency." Is this right?
2. When measuring the frequency response of a system, the convention is to define the half power limits as a function of the mid band value. Half power is chosen simply because it's a convenient figure which is easy to calculate with.

i.e. the frequencies at which the signal output is -3db either side of the average (usually r.m.s.) midband value and it is this for which the bandwidth of a system is quoted.

A frequency range is simply all the frequencies between a given upper and lower frequency limit with no reference to power or amplitude.

For example: An audio system could have a frequency range of d.c. to 100khz but this would be meaningless because it says nothng about how flat or otherwse the systems response is over that range. Hence a quoted bandwidth of say 20Hz to 45kHz may be stated which defines the frequency response as staying within +/- 3db between those frequencies.

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