# Extracting a sinewave signal when characteristic phase and frequency are known

• tchetch
In summary, the conversation discusses a problem with a sine wave signal contaminated by noise and the search for its magnitude at a specific phase and frequency. Suggestions are made to filter out noise, use peak detection or RMS calculation, and consider aliasing or sampling rate issues. The mention of Tom Irvine's method for sine function identification and removal is also brought up, as well as a potential solution using a numerical filter. The conversation also references Tom's website, www.vibrationdata.com.
tchetch
Hi there,

i have this problem:
I have a sinewave signal contaminated by a large amount of noise. I already know the phase of the signal and its characteristic frequency, and I am searching for its magnitude.

If I do a basic Fourier transform, I would obtain the magnitude at its characteristic frequency, but the phase would be generally shifted. Does anyone know a way to extract the magnitude at its specific phase and frequency ?

Filter out the noise and then do peak detect? Or just take the RMS of the signal, and calculate the peak value (adding or subtracting an offset as necessary)?

I don't understand how a sine wave can have absolute phase?

Is it truly noise or have you considered it could be an aliasing issue? Have you treid playing with the sampling rate?

I was also looking through some old notes I have. Tom Irvine over at Vibrationdata.com published a quick paper regarding a method he wrote a small program for, called sinefind. The paper is entitled "Sine Function Identification and Removal." I can't post it here because it is Tom's work. It pulls out amplitude, frequency and phase by a curve fit method.

If you have any interest in vibration analysis, take a look over at Tom's website.

www.vibrationdata.com

There is a type of numerical filter than can do this, but the name escapes me right now. Is the noise gaussian or normal?

## 1. How do you extract a sinewave signal when the characteristic phase and frequency are known?

To extract a sinewave signal, you can use a process called demodulation. This involves multiplying the signal by a local oscillator with the same frequency and phase as the original signal, and then filtering out the high frequency components to leave only the desired sinewave signal.

## 2. Can this method be used for any frequency and phase of the signal?

Yes, demodulation can be used for any frequency and phase of the signal as long as the local oscillator has the same frequency and phase as the original signal. This means that the method is not limited to only extracting sinewave signals, but can also be used for other types of signals.

## 3. What types of equipment are needed for this extraction process?

You will need a signal source with known frequency and phase, a local oscillator with the same frequency and phase, and a filter to remove the high frequency components. This can be achieved using various types of equipment such as signal generators, mixers, and filters.

## 4. Is this extraction process accurate and reliable?

Yes, when all the necessary parameters are set correctly, the extraction process can be very accurate and reliable. However, any imperfections in the equipment or slight variations in the frequency and phase of the signal can affect the accuracy of the extracted sinewave signal.

## 5. Are there any limitations to this extraction method?

One limitation of this extraction method is that it requires prior knowledge of the frequency and phase of the signal. If this information is not available, then this method cannot be used. Additionally, any noise or interference in the signal can affect the accuracy of the extracted sinewave signal.

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