In a message dated 21/07/2005, gcouger@.......... writes:

Chris,

I am not looking for water levels I putting out sensors  and making a shock 
moving over and making another shock ....I need a post  process GPS signal to 
know where 
I am I might as well use the time spruce  on it.
Hi Gordon,
 
    I understand now. We used chains of hf geophones  and a pneumatic 
hammer.... Sure you need te position accurately as well. Do you  use relative GPS to 
give you accuracies down to a few cm? 

Almost  everything I work with has a GPS. I did the first vehicle units for  
www.ipsolutionsinc.com and all the software for spryer in  
http://www.ppi-far.org/ppiweb/bcrops.nsf/$webindex/6041B8CEFFC83068852568F1005
6A8F7/$file/97-4p15.pdf!open
    Interesting, but availablily depends on the roots  being able to find 
nutrients and hence on the rainfall & intensity. It  probably would not work too 
well for things like moss and poor land grasses. The  grab every nutrient 
molecule going and store them. This was the problem in  Finland after the 
Chernobyl nuclear disaster. The grasses and moss which fed the  reindeer heards soaked 
up most of the radioactivity.

I agree  they are power hogs and take a lot of resources for time 
for seismic  senors that VLF will do just as well as GPS. I have 
seen jitter on VLF  from WWV in a really bad magnetic storm but 
not as often as I have lost  lock with the GPS.
    I don't get this problem at all often. The computer  looks for an 
interference free minute every half hour and then adjusts the  precision crystal 
oscillator offset on the 59 mean pulses. The drift is  initially set at less than 
5 ppm and can be maintained down parts in 10^8

If you  want to time sync a signal on a sound card you can depend 
on windows for  time. It is too uncertain when the windows 
routine will time stamp it.  Windows can't be made work in real time.
    Where are you getting your time stamp from? I  definitely can't rely on 
either the software or the hardware clocks on the  board.

If you  want to record 0 to 20 Hz signals on a sound card a mixer and local 
oscillator  at 500 Hz will move the 0 to 20 Hz to 500 to 520 and the inverse of 
it to 480  to 500. You can use DSP to get the signal back from either one.

Ten  bits is enough for most situations in vehicles any more is lost in the 
noise  of the vehicle. In the case of seismometer in an open field a more 
sensitive  A/D could be used.


Regards,
 
    Chris Chapman





In a message dated 21/07/2005, gcouger@.......... writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20
  size=3D2>Chris,

I am not looking for water levels I putting out sen=
sors=20
  and making a shock moving over and making another shock ....I need a post=20
  process GPS signal to know where 
I am I might as well use the time spr=
uce=20
  on it.
Hi Gordon,
 
    I understand now. We used chains of hf geophone=
s=20
and a pneumatic hammer.... Sure you need te position accurately as well. Do=20=
you=20
use relative GPS to give you accuracies down to a few cm? 
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>Almost=20
  everything I work with has a GPS. I did the first vehicle units for=20
  www.ipsolutionsinc.com and all the software for spryer in=20
  
http://www.ppi-far.org/ppiweb/bcrops.nsf/$webindex/6041B8CEFFC83068852=
568F10056A8F7/$file/97-4p15.pdf!open
    Interesting, but availablily depends on the roo=
ts=20
being able to find nutrients and hence on the rainfall & intensity. It=20
probably would not work too well for things like moss and poor land grasses.=
 The=20
grab every nutrient molecule going and store them. This was the problem in=20
Finland after the Chernobyl nuclear disaster. The grasses and moss which fed=
 the=20
reindeer heards soaked up most of the radioactivity.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>I agree=20
  they are power hogs and take a lot of resources for time 
for seismic=20
  senors that VLF will do just as well as GPS. I have 
seen jitter on VLF=
=20
  from WWV in a really bad magnetic storm but 
not as often as I have los=
t=20
  lock with the GPS.
    I don't get this problem at all often. The comp=
uter=20
looks for an interference free minute every half hour and then adjusts the=20
precision crystal oscillator offset on the 59 mean pulses. The drift is=20
initially set at less than 5 ppm and can be maintained down parts in 10^8
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>If you=20
  want to time sync a signal on a sound card you can depend 
on windows f=
or=20
  time. It is too uncertain when the windows 
routine will time stamp it.=
=20
  Windows can't be made work in real time.
    Where are you getting your time stamp from? =
I=20
definitely can't rely on either the software or the hardware clocks on the=20
board.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>If you=20
  want to record 0 to 20 Hz signals on a sound card a mixer and local oscill=
ator=20
  at 500 Hz will move the 0 to 20 Hz to 500 to 520 and the inverse of it to=20=
480=20
  to 500. You can use DSP to get the signal back from either one.

Ten=
=20
  bits is enough for most situations in vehicles any more is lost in the noi=
se=20
  of the vehicle. In the case of seismometer in an open field a more sensiti=
ve=20
  A/D could be used.


    Regards,
 
    Chris Chapman