How to get rid of unwanted noise from a signal?

Question

I am trying to get rid of noise of 60 hz ( its continuous) from another continuous signal of 61 Hz. I have been working with several methods but none of them has been 100% efficient. I am doing everything in MATLAB.

Answer 1

If only your signal were a little higher, I'd recommend using a simple high-pass (RC) filter. It's hard to build something, though, that can descriminate effectively between such close frequencies. You can build a band-stop to block the 60hz, but to do it and allow a 61hz signal to pass is going to be more difficult (narrow-band, hi Q-value, probably a bit more expensive). I think they make anti-hum filters to do exactly that, but I'm not sure how wide of a band they block.

Answer 2

61 hz is a tough signal to deal with because you can't filter out 60 hz. 60 hz noise usually comes from the A/C power source (in USA; it's 50 hz in Europe). Proper grounding helps; sometimes it helps to switch hot and neutral (if you have ungrounded 2-prong plug). Check your power source for proper ground. A dedicated curcuit may help, i.e., no other appliances on the curcuit. If you have loads of cash and time, build a Faraday cage, aka screen room; ground the screen and feed only the d.c. power thru a hole in the screen.

Answer 3

Instead of theoretically trying to extract it, you could try using a difference amplifier to obtain the raw signal, with one channel set up to pick the 60Hz. Otherwise, if the signal is fairly simple, do a Fourier series out to something huge and then extract the 60Hz term before reconstruction. You may lose some information on the actual signal though, if it's more than just a 61hz sine wave.

Answer 4

Signal cannot be 61 Hz exactly, because in that
case it carries no information. Signal always
occupies a range of frequencies, for example
from 60.5Hz to 61.5Hz.

If it's not signal, but simply two sinusoidal waves,
than you can separate them using notch filters.
SInce your frequency is very low digital filters
are prefered by far (follow second link for example)