I want to sample two signals, S and R and later do IQ demodulation on these.
I am multiplying S with R and I also want to multiply S with a 90 degree phase shifted version of R by shifting the samples in R so I get a 90 degree phase shift. The problem I encounter with this is that unless I have a sampling rate that is 4*n of the sine signal frequency (where n is an integer) I wont be able to phase shift the R signal by 90 degrees. And this is my case as the sampling rate and the signal frequency are not in this multiple of each other. So let's say I am able to do a 82 degree phase shift. Is it then possible to correct for this somehow for the total number of periods I choose to sample?
Does it at all give any additional information when doing IQ demodulation when I phase shift the reference signal by shifting the samples to get a 90 degree phase shift?
EDIT: Measuring range is 3k->300k Hz. S is a single frequency sine wave and R a square wave.