Hi Dave, I would like to see a picture of the ASMET - 1V MET seismometer. It
sound like an interesting system.  I live near the beach myself, in Aptos
near Santa Cruz, and the ocean microseisms area very distinct here most of
the time. Do you happen to have a logic diagram of your filter you designed?
It might be just the thing I need for my Lehman's. As for my setup, like
you, I also have three HS-10's. I use Larry's WINSDR with a GPS clock and
Winquake. I'm very happy with the hardware and the software. In the past, I
used IBM 12-bit A/D boards and ran two AT systems. In it's day it was a good
setup. If you want to take a look, my website is at
http://pw2.netcom.com/~shammon1/psnsj.htm and you can see some pictures of
my old system with the AT's installed. The Lehman's and HS-10 are in the
photos. I'm working on some newer photos of the electronics and will have
them up on the site in the next week or two.
Regards, Steve Hammond PSN San Jose, Aptos CA
  -----Original Message-----
  From: psn-l-request@.............. [mailto:psn-l-request@.................
Behalf Of Dave Nelson
  Sent: Wednesday, February 23, 2005 11:53 PM
  To: PSN-L@..............
  Subject: Microseism filter


  I have recently added a Russian ASMET -1V MET broadband seismometer to my
setup. As I live near the coast the microseism level was dominating the
noise backgrond to the extent that earthquakes of interest were being lost
in the " noise". The microseism spectrum is very distinct and I felt  its
elimination  would not seriously effect the earthquake detection capability
.

   I have developed a simple filter based on switched capacitor technology
that virtualy eliminates the microseism background. The filter has no
critical componants or  capacitors and is tuned by a clock frequency. The Q
is 0.5 which gives roughly an octave bandwidth centered at 0.015 hz or 6.6
seconds . Since the center frequncy is clock dependant it can be shifted
arbitarily but 6.6 seconds seems to work very well. The filter is placed
directly ahead of the A/D at the highest voltage swing  level in the system
to avoid adding noise.  Just two wires -- in and out (plus power of course).

  The results are very good, the harmonic like signal from microseism is
gone and the effective signal to noise ratio of eathquakes is significantly
better. The spectrum has a deep null at 6.6 seconds instead of a  dominant
peak .

  I know this kind of spectrum shaping can be easily done in software but
that is usually beyond the scope of an amateur or computer dum- dum like me.
The whole thing is  two IC's and a 15 hz clock generator. ( 100 times the
center frequency)

  The Russian seismometer is truely amazing. Virtually plug and play -- four
wires ,no adjustments or critical setup. The respose is advertised to 20
seconds but seems to respond well to over 100 seconds on the low end and too
well to be useful ,given the urban background noise ,at the high frequency
end. I have another swiched capacitor low pass filter switchable to 5, 2.5
and 1.25 hz. to control the high end cutoff.

  My setup also includes 3 axes of short period based on HS-10-1  1 hz
seismometers that I found in a surplus store. I am using Amaseis and
experimenting with Seismowin for analysis and display.

  I am a retired aerospace engineer who spent too much of my career in
management and I am having a ball doing the seismology thing.Good to be back
doing some development and putting the old brain to work. I intend to do
some seismometer development as my next project -- I have some ideas for
some different ,but not outrageous, concepts which may ( or may not ) work.

  I would be glad to correspond with anyone interested in or commenting on
what I am doing.


  Dave Nelson   ( California not New Zealand)







Hi=20
Dave, I would like to see a picture of the ASMET - 1V MET seismometer. =
It sound=20
like an interesting system.  I live near the beach myself, in Aptos =
near=20
Santa Cruz, and the ocean microseisms area very distinct here most of =
the time.=20
Do you happen to have a logic diagram of your filter you designed? It =
might be=20
just the thing I need for my Lehman's. As for my setup,=20
like you, I also have three HS-10's. I use Larry's WINSDR with a GPS =
clock and=20
Winquake. I'm very happy with the hardware and the software. In the =
past, I used=20
IBM 12-bit A/D boards and ran two AT systems. In it's day it was a good =
setup.=20
If you want to take a look, my website is at http://pw2.netcom.com/=
~shammon1/psnsj.htm and=20
you can see some pictures of my old system with the AT's installed. =
The=20
Lehman's and HS-10 are in the photos. I'm working on some newer photos =
of the=20
electronics and will have them up on the site in the next week or=20
two.  
Regards, Steve Hammond PSN San Jose, Aptos =
CA

  
-----Original Message-----
From: =
psn-l-request@.................
  [mailto:psn-l-request@...............On Behalf Of Dave=20
  Nelson
Sent: Wednesday, February 23, 2005 11:53 =
PM
To:=20
  PSN-L@..............
Subject: Microseism =
filter


  
I have recently added a =
Russian ASMET -1V=20
  MET broadband seismometer to my setup. As I live near the coast the =
microseism=20
  level was dominating the noise backgrond to the extent that =
earthquakes of=20
  interest were being lost in the " noise". The microseism spectrum is =
very=20
  distinct and I felt  its elimination  would not =
seriously=20
  effect the earthquake detection capability .
  
 
  
 I have developed a simple =
filter based on=20
  switched capacitor technology that virtualy eliminates the microseism=20
  background. The filter has no critical componants or  capacitors =
and is=20
  tuned by a clock frequency. The Q is 0.5 which gives roughly an =
octave=20
  bandwidth centered at 0.015 hz or 6.6 seconds . Since the center =
frequncy is=20
  clock dependant it can be shifted arbitarily but 6.6 seconds seems to =
work=20
  very well. The filter is placed directly ahead of the A/D at the =
highest=20
  voltage swing  level in the system to avoid adding noise.  =
Just two=20
  wires -- in and out (plus power of course).
  
 
  
The results are very good, the =
harmonic like=20
  signal from microseism is gone and the effective signal to noise ratio =
of=20
  eathquakes is significantly better. The spectrum has a deep null =
at 6.6=20
  seconds instead of a  dominant peak .
  
 
  
I know this kind of spectrum shaping =
can be=20
  easily done in software but that is usually beyond the scope of =
an=20
  amateur or computer dum- dum like me. The whole thing is  two =
IC's and a=20
  15 hz clock generator. ( 100 times the center frequency)
  
 
  
The Russian seismometer is truely =
amazing.=20
  Virtually plug and play -- four wires ,no adjustments or critical =
setup. The=20
  respose is advertised to 20 seconds but seems to respond well to over =
100=20
  seconds on the low end and too well to be useful ,given the=20
  urban background noise ,at the high frequency end. I have another =
swiched=20
  capacitor low pass filter switchable to 5, 2.5 and 1.25 hz. to control =
the=20
  high end cutoff.
  
 
  
My setup also includes 3 axes of =
short period=20
  based on HS-10-1  1 hz seismometers that I found in a surplus =
store. I am=20
  using Amaseis and experimenting with Seismowin for analysis and=20
  display.
  
 
  
I am a retired aerospace engineer who =
spent too=20
  much of my career in management and I am having a ball doing the =
seismology=20
  thing.Good to be back doing some development and putting the old brain =
to=20
  work. I intend to do some seismometer development as my next project =
-- I have=20
  some ideas for some different ,but not outrageous, concepts which =

  may ( or may not ) work. 
  
 
  
I would be glad to correspond with =
anyone=20
  interested in or commenting on what I am doing.
  
 
  
 
  
Dave Nelson   ( California =
not New=20
  Zealand)