Re: What is Nyquist Rate
So, the sampled signal has periodic spectrum. (So it will be infinity)
It will be periodic with the sampling frequency.
Try it, for example draw a simple spectrum, and pushing along the spectrum with sampling frequency. If the sampling frequency isn't large enough then the spectrum will be "aliasing".(Subsampling) But in some application the subsampling is useful.
Shannon has the theory about sampling. This is true, if your signal is real and bandlimited.
So, if you use Nyquist rate as sampling frequency, you can take it for sure, that no loss of information will occur subsequent upon aliasing.
Nyquist frequency(rate)=2* highest frequency in your signal (baseband signal) , so the two-sided bandwith of the signal
And then you can use a low pass filter to reduce the bandwith from infinity
In the Communication Theory, there's an idea of Nyquist channel characteristics. It's because of avoid ISI (Inter Symbol Interference)