I am an amateur seismographer, located in Locust Valley, NY. My  station 
consists of home built sensors of rather short natural period. Out of  necessity, 
I have developed a digital inverse filter, which allows extension of  the 
natural period of the sensors to five or more times their natural period. It  took 
a lot of grunting and straining to perfect this filter, and I want to share  
it with anybody who could benefit. It ended up being simple to code and use. 
All  you need to set it up is the natural period and damping of the sensor, and 
the  desired filter period. It can be used in real time or on completed files.
 
  In case you have any need to enhance the performance of geophones or  any 
other open loop sensor you operate, please refer to web page 
 
  _http://www.jclahr.com/science/psn/mcclure/filter.html_ 
(http://www.jclahr.com/science/psn/mcclure/filter.html) 
 
  This page describes the analog prototype of the filter and the  pseudocode 
for its digital version. A mathematical analysis demonstrates that  the 
filter's frequency response is correct.
 
  This filter is implemented in my programs "WQFilter.exe" and  
"Heliplot.exe", which can be downloaded from
 
  _http://www.jclahr.com/science/psn/mcclure/wdq_utilities/index.html_ 
(http://www.jclahr.com/science/psn/mcclure/wdq_utilities/index.html) 
 
  "WQFilter.exe" is a utility program for filtering WinQuake PSN Type  4 
event files. "Heliplot.exe" is a program for filtering and displaying Dataq  WQD 
format files. It would be easy for me to code these applications for other  
file formats, including Little Endian SAC binary files.
 
  Dr. Alan Jones has also incorporated this filter into "AmaSeis.exe"  for 
filtering SAC binary format event files. However, the version he has coded  is 
no longer up-to-date, and the response is not quite so accurate as the latest  
version.
 
  All my applications are written using Visual Basic 6.0 for Windows.  Alan 
is currently re-coding Amaseis using Java, so that it can be compiled for  
other operating systems.
 
  Please note that "WQFilter.exe" also includes Butterworth filters  for 
lowpass and highpass filtering. Forward, backward, and forward-backward  filtering 
can be selected. If you apply both my period extending filter and a  second 
order highpass backward filter to the event data, you can end up with a  
broader bandwidth file which has no phase distortion and no time delay in  the 
passband.
 
Robert (Bob) McClure



************************************** See what's free at http://www.aol.com.





  I am an amateur seismographer, located in Locust Valley, NY. My=20
station consists of home built sensors of rather short natural period. Out o=
f=20
necessity, I have developed a digital inverse filter, which allows extension=
 of=20
the natural period of the sensors to five or more times their natural period=
.. It=20
took a lot of grunting and straining to perfect this filter, and I want to s=
hare=20
it with anybody who could benefit. It ended up being simple to code and use.=
 All=20
you need to set it up is the natural period and damping of the sensor, and t=
he=20
desired filter period. It can be used in real time or on completed files.
 
  In case you have any need to enhance the performance of geophone=
s or=20
any other open loop sensor you operate, please refer to web page 
 
  http://www.jc=
lahr.com/science/psn/mcclure/filter.html
 
  This page describes the analog prototype of the filter and the=20
pseudocode for its digital version. A mathematical analysis demonstrates tha=
t=20
the filter's frequency response is correct.
 
  This filter is implemented in my programs "WQFilter.exe" and=20
"Heliplot.exe", which can be downloaded from
 
  =
http://www.jclahr.com/science/psn/mcclure/wdq_utilities/index.html
 
  "WQFilter.exe" is a utility program for filtering WinQuake PSN T=
ype=20
4 event files. "Heliplot.exe" is a program for filtering and displaying Data=
q=20
WQD format files. It would be easy for me to code these applications for oth=
er=20
file formats, including Little Endian SAC binary files.
 
  Dr. Alan Jones has also incorporated this filter into "AmaSeis.e=
xe"=20
for filtering SAC binary format event files. However, the version he has cod=
ed=20
is no longer up-to-date, and the response is not quite so accurate as the la=
test=20
version.
 
  All my applications are written using Visual Basic 6.0 for Windo=
ws.=20
Alan is currently re-coding Amaseis using Java, so that it can be compiled f=
or=20
other operating systems.
 
  Please note that "WQFilter.exe" also includes Butterworth filter=
s=20
for lowpass and highpass filtering. Forward, backward, and forward-backward=20
filtering can be selected. If you apply both my period extending filter and=20=
a=20
second order highpass backward filter to the event data, you can end up with=
 a=20
broader bandwidth file which has no phase distortion and no time delay =
in=20
the passband.
 
Robert (Bob) McClure


=
See what's free at AOL.com.