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- What is the significance of -3dB? 5 answers
I am looking at this page and coming from little EE knowledge, it left me confused. First of all, it defines bandwidth as the following
Bandwidth is defined as the measure of a circuit or transmission channel to pass a signal without significant attenuation over a range of frequencies. Bandwidth is measured between the lower and upper frequency points where the signal amplitude falls to -3 dB below the pass-band frequency. The -3 dB points are referred to as the half-power points.
Can someone explain that more simply? Also why is -3 dB considered half-power points. This definition kinda sounds like those coaxial cable splitters you can get for your home that have a frequency range printed on them. Is that what this definition is applying to?
Then I have a question about this part:
If you input a 1 V, 100 MHz sine wave into high-speed digitizer with a bandwidth of 100 MHz, the signal will be attenuated by the digitizer’s analog input path and the sampled waveform will have amplitude of approximately 0.7 V. The value of ~0.7 V can be calculated by using the following equation: -3 dB = 20 LOG (Vppout / Vppin)
Why would inputting 1 volt peak to peak 100mhz sine wave into a digitizer output 0.7 volts peak to peak. I have heard Nyquist–Shannon sampling theorem said, but don't really understand it from a working standpoint (I assume it is applying here). If a signal is coming up at 100mhz and you are taking 100mhz samples, wouldn't that be enough to duplicate the 1 volt peak to peak signal? Also, how is the -3 dB applying to that formula? I don't see how it is involved.