Hi Bob and Karl,

I'm not sure I got what you were looking for, but gave it a try.  See: 
http://bnordgren.org/seismo/TvsFBV02.jpg    This is a screen capture of two 
instruments recorded during a quiet time this morning.  The upper trace is 
the FBV and the lower one is the Trillium.  We have been looking at data 
like this for quite a few months, with the goal of getting the noise at all 
frequencies of interest, reduced to the absolute minimum possible.

The p-p signal for the larger 'wiggles' is about 10-15 counts which x the 
sensitivity for this particular FBV of about 14.4 nm/s/count gives roughly 
200 nm/s p-p of seismic noise.  Most of the noise appears to be from 
microseism energy below the 12.5 sec 6-pole low-pass filter cutoff 
frequency.  It is clear from comparing the two traces that in the frequency 
range used here, 50 sec. to 12.5 sec., the instrument noise is somewhat 
smaller than the seismic background, probably only a few counts p-p.  Note 
that the gain of the Trillium here is about 17% higher than the 
FBV.  WinSDR doesn't let me fine tune it to the same degree that I can in 
WinQuake.

The initial transient is WinSDR's filter response to a DC offset, which in 
this case was larger for the FBV.  Usually the Trillium has the greater 
offset as it seems to have a significantly larger response to temperature 
change rates.

At this point I am certain that the FBV instrument noise will be smaller 
than the seismic background in all but the quietest amateur locations.  Of 
course there is always the ANMO borehole in New Mexico.  That's pretty quiet!

Let me know what else might be of interest.

Regards,
Brett


At 11:37 AM 9/12/2009 +0000, you wrote:
>The seismograms look like they came from the same sensor to me.  But...if 
>they didn't, I'll be building one of your FBV instruments!
>
>Could you show us another two seismograms with background noise and then 
>physically/electrically offset the FBV to identify it?
>
>Regards,
>
>Bob Hammond
>PSN-Alaska
>http://wulik.com

Watch our wiggles
http://bnordgren.org/seismo/gif_images.htm

or watch some very very good wiggles
http://aslwww.cr.usgs.gov/Seismic_Data/telemetry_data/ANMO_24hr.html


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