Hi All,

A few days ago, Dave Nelson in California was able to obtain the loan of a 
Nanometrics Trillium Compact-120, a professional quality triaxial packed 
into a can only slightly larger than a large geophone.  Our plan is to 
compare its output with the home-built Force Balance Vertical running 
beside it.

Soon after it was installed, California obliged with a nice 3.9 up the 
coast which gave us a modest sized test signal containing some higher 
frequency energy, which we could use to compare the two instruments.  Both 
instruments' outputs were filtered with a 20Hz 4-pole low pass and the 
Trillium had a two pole high-pass added at 1/50Hz, in order to match the 
50-second low frequency rolloff of the FBV, since its own rolloff was at 
120 seconds.

The results are shown at http://bnordgren.org/seismo/TvsFBV01.gif  or the 
somewhat larger  http://bnordgren.org/seismo/TvsFBV01.jpg

Question:  Which is the $7000 Trillium and which is the FBV built by Dave?

Regards,
Brett .


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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