Dave
The "real-time period extending  filter in WinSdr". Is that the high pass/ low 
pass digital filter located with each channel or is there something else in the 
program that I'm not aware of ?
 Regards
Barry
www.seismicvault.com






________________________________
From: Dave Nelson 
To: psnlist@..............
Sent: Thu, December 27, 2012 3:33:06 PM
Subject: Re: Instrumentation Question


Hi Bob,
 
I have tried the real-time period extending  filter in WinSdr with very good 
results . I am using it to extend the  period of broadband force balance 
seismometers from 50 or 120 seconds to 1000  seconds   I know that was not the 
original intent but it really works  well.  I have compared its performance with 
an analog "inverse filter" with  essentially the same transfer function .The 
resulting waveforms are essentially  identical.  

 
I have not yet tried the WinQuake version but I will do so
 
My objective is to provide a system with  real-time capability to observe earth 
normal modes following a large event and  analyze the spectrum with WinQuake.  
The increase in noise at  very  long periods is clearly evident but that is 
expected and OK. The noise source   is mostly the instrument self noise enhanced 
by the period extension  filter since the instrument noise is significantly 
above the low noise model  beyond 100 seconds. The very long period waveforms 
from side by side broadband  instruments are incoherent but they will 
be coherent  following a  large teleseismic event upon excitation of the Normal 
modes. The period  extension process could be either in the data acquisition as 
I am now doing , or  in post processing using  WinQuake. The pros do it in post 
processing  but they don't get so excited watching waveforms in real time like 
the  amateurs. 
 
Just one comment on the relative merits of the  inverse  filtering techniques 
vs. the negative impedance loading for a  geophone. When filtering a critically 
damped geophone the geophone dynamics are  unchanged and the clipping level is 
unchanged. When the geophone is loaded with  a negative impedance the dynamics 
of the seismic mass are changed dramatically.  The mass is heavily over-damped 
and  moves much less in response to large  ground displacements. One of the 
problems in seismic instrumentation for public  safety is clipping. The 
over-damped geophone has a much larger dynamic  range as well as period 
extension.
 
Thanks for the heads up on WinQuake and sorry for  the overly long response. 
This is really interesting stuff and it gets me going  :-} 

 
Best Regards,
 
Dave
The "real-time period extending 
filter in WinSdr". Is that the high pass/ low pass digital filter located with each channel or is there something else in the program that I'm not aware of ?
 
Regards
Barry
www.seismicvault.com



From: Dave Nelson <davefnelson@.......>
To: psnlist@..............
Sent: Thu, December 27, 2012 3:33:06 PM
Subject: Re: Instrumentation Question




 
 

Hi Bob,
 
I have tried the real-time period extending 
filter in WinSdr with very good results . I am using it to extend the 
period of broadband force balance seismometers from 50 or 120 seconds to 1000 
seconds   I know that was not the original intent but it really works 
well.  I have compared its performance with an analog "inverse filter" with 
essentially the same transfer function .The resulting waveforms are essentially 
identical.  
 
I have not yet tried the WinQuake version but I will do so
 
My objective is to provide a system with 
real-time capability to observe earth normal modes following a large event and 
analyze the spectrum with WinQuake.  The increase in noise at  very 
long periods is clearly evident but that is expected and OK. The noise source 
 is mostly the instrument self noise enhanced by the period extension 
filter since the instrument noise is significantly above the low noise model 
beyond 100 seconds. The very long period waveforms from side by side broadband 
instruments are incoherent but they will be coherent  following a 
large teleseismic event upon excitation of the Normal modes. The period 
extension process could be either in the data acquisition as I am now doing , or 
in post processing using  WinQuake. The pros do it in post processing 
but they don't get so excited watching waveforms in real time like the 
amateurs. 
 
Just one comment on the relative merits of the 
inverse  filtering techniques vs. the negative impedance loading for a 
geophone. When filtering a critically damped geophone the geophone dynamics are 
unchanged and the clipping level is unchanged. When the geophone is loaded with 
a negative impedance the dynamics of the seismic mass are changed dramatically. 
The mass is heavily over-damped and  moves much less in response to large 
ground displacements. One of the problems in seismic instrumentation for public 
safety is clipping. The over-damped geophone has a much larger dynamic 
range as well as period extension.
 
Thanks for the heads up on WinQuake and sorry for 
the overly long response. This is really interesting stuff and it gets me going 
:-} 
 
Best Regards,
 
Dave