Howdy From GVA;
The electrical grounds in the desert here are
practically non existent and you need to
create your own. I have used a general purpose
tester that tells me my wiring is correct
but more than likely the ground is very
high resistance. I am tying B- to earth ground
even tho I use a split supply since it is the
only common ground I am able to share with
the devices I have. There are 12800V lines
I believe within 50 ft of this place and seem
to create a terrific AC field over the whole area.

I am glad to see someone take an interest
in this ground thing since I have over
the years never got it exactly right.

Since reprogramming for 12 bits
reducing my time to 30 minutes of recording
I now see a strong artifact I believe
to be alised from a higher frequency.

I had to reduce my amplifier gain
by a factor of eight so this artifact
must be presenting itself directly
to the A/D converter but still not sure.
Amplifier GAIN FROM X10,000 to X1250 I believe
at one hertz. The A/D I use went from
8mv per count to 1mv per count.
The overall sensitivity should be the same
for seismic signals but has increased for
electrical artifacts.

I can provide you with raw INTEGER data
but not the final results of any analysis
since I also must rewrite the display
routine to create WINQUAKE and the BMP
and WAVE files I regularly use.
This raw data with associated data
may be of use to anyone wanting to
understand what I'm dealing with here.

I have noticed a different picture
with 12 bits but not sure I am able to
get full scale since my opamps will not go
rail to rail.

The picture looks promising even tho
there are electrical artifacts present.

You would not believe the ground noise
I have here at audio frequencies this place
a cornucopia filled with air conditioners running
all at the same time.

Thanks for the reply.
I'm trying now to straighten
the 12 bit thing out and
will be offline awhile.

I understand the basic idea of a ground
but have only been able to make it
partially work.
So I'm obviously lacking understanding.
My formal training is military schools
and civilian associates degree which
as anyone knows only serves to get
ones foot in the door and nothing like
those 500 series courses of study.

I find this all rather entertaining though.

Best regards;
geoff




----- Original Message ----- 
From: 
To: 
Sent: Sunday, October 25, 2009 6:47 PM
Subject: Re: Event 091025.105300 as seen from GVA ??


> 
> In a message dated 26/10/2009, gmvoeth@........... writes:
> 
> But  think not able to go higher than 10 bits since the lower two seem 
> noisy and I  do not understand why since with no input but a dummy 5K resistor I 
> see the  lower bits bouncing with no input at all.
> 
> 
> 
> Hi Geoff,
> 
>    Have you checked your electricity supply that line  really is line and 
> return is ~zero?
> 
>    Regards,
> 
>    Chris Chapman
>
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