Re: 60Hz Notch filter at 25kHz sampling rate?

On Aug 28, 6:20 pm, "SteveSmith" <Steve.Smi...@xxxxxxxxxxxxxxx> wrote:
Hello,

I have an ENG signal, sampled at 25kHz that has high mains interference
that I want to remove.  The problem is I need the surrounding
frequencies,
maybe not 50-70, but I can't afford to sacrifice much more than this.
The
filter designs I've been looking at don't seem to be able to do this at
such a high sampling rate.  

Any suggestions?  Would downsampling help?

Thank you in advance for your help

Allison  

Hi Allison,
Here's a simple IIR notch filter that you can try. Feel free to e-mail me
with questions.
Steve

http://www.dspguide.com/ch19/3.htm- Hide quoted text -

- Show quoted text -

Hi Steve,

Some considerations for using this filter for the OP. It would seem
that the biggest possible problem using this filter at a narrow
bandwidth is that the stopband width (defined as frequency range for
gain below some attenuation threshold) for a reasonable attenuation is
quite narrow. The frequency plots (I didn't check the equations) look
like they have a zero at the notch frequency and the gain rises
rapidly to either side. That means if the frequency is not almost
EXACTLY at the notch frequency, or if there is a small variation in
the frequency (unintentional frequency modulation, amplitude
modulation, frequency drift), the attenuation may decrease
dramatically. If any of these cases regarding the frequency is the
case, and a lot of attenuation is required, the OP would need to
consider a wider stopband width filter, hopefully one that doesn't
have to have an excessive increase in bandwidth. I am not saying the
OP can't use the filter for his application, just some things to
consider.

Given the ENG application it would seem that power line frequency
harmonics may also be a problem the OP has to deal with.

Dirk
.

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