PSN-L Email List Message

Subject: Re: High noise >10s
From: Geoff gmvoeth@.........
Date: Thu, 02 Aug 2012 12:36:28 +0000


I would recommend first increasing your sample rate
to rule out Alizing issues.
You can not filter out Alizing issues which result
in artifacts within the band of interest,
You need a filter like n-16 to really eliminate
artifacts close to the cutoff frequency.
Until you do this, you can not be sure
the signal is genuine.
If you increase sample rate to like 500sps
and these artifacts disappear then you know
what they really are.

regards,
geoff



On 2012-07-30 2:07, Tiago A. wrote:
> Hi.
>
> Im using a L4 1Hz geophone and for almost a month im struggling with
> high noise from 10s up to ..., but from <10s it looks good. The noise
> comes and goes, this image is self explaining:
>
> http://dl.dropbox.com/u/15802004/noise.png
>
> Changed cables, re centered the geophone, but didint help..the geophone
> is connected directly to a ADC without damping, external amplification
> or filtering, i only use digital filtering from the ADC. Before this
> issue start, i had a pretty clean spectrum >10s for almost 6 months,
> which allowed me to received LQ and LR from some strong events.
>
> This sac contains 15minutes with high noise >10s, notice that at 3:37 it
> recorded a Ml2.1 at 70km.
> http://dl.dropbox.com/u/15802004/noise.sac
>
> What could be the problem?
>
> I appreciate any help.
>
> Best Regards,
> Tiago.
>
>
>


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