PSN-L Email List Message

Subject: Re: Omnidirectional instrument
From: Geoff gmvoeth@.........
Date: Tue, 01 Jan 2013 07:00:55 +0000


On 12/31/2012 5:54 PM, chrisatupw@....... wrote:
> From: Geoff 
> To: psnlist 
> Sent: Mon, 31 Dec 2012 10:56
> Subject: Re: Omnidirectional instrument
>
> I'm just interested in first time of arrivalas well as distance and depth but
>
> not so muchabout axis. Possibly magnitude.
>
> I think the plane of arrivalcan be extracted from three or more sites with
> timing which is both accurate and precise.
> At least GPS quality.
>
> Hi Goeff,
>
>
>
>      You don't need GPS quality timing. And  a multitasking computer can't record it to
>
> anything liketheaccuracy of the received signal. They run on an interrupt cycling
>
> system several hundred times a second.
>
>      P waves usually have a velocity of 6 to 8 km / sec depending on depth, so if you
>
> know the time correct to the nearest 1/10 of a second, this is good enough for our type
>
> of seismology. You can get this easily from WWVB  signals - but NOT over the Internet.
>
>
>
>      Regards,
>
>
>
>      Chris Chapman
>
>         
>
>      
>
I think the timing and everything are related to the A/D board type III
and not the computer running the WINSDR program. Every check I have made
using even WWV 10MHz has come out well.
I would agree with you If I were using my old hommade setup which
ran on a 16 bit program under MSDOS622 and run in a loop
doing things between taking samples at the tic counter rate.

You'll probably be happy to hear that I have returned to the
traditional negative input Opamp design and limited the spectrum
between 2Hz and 10 seconds. I found the noise at > 10seconds
to be unacceptable with 20seconds even dummy loaded.
I was unable to beat the noise back to acceptable levels.

When I redo the filter section I will lower the overall gain
and hopefully also the overall noise.

I expect possibly about 73Dbv overall gain in two sections
with the post amp/LPfilter being the second.

Regards & happy New year 2013,
geoff





  
    
  
  
    
On 12/31/2012 5:54 PM, chrisatupw@....... wrote:
From: Geoff <gmvoeth@...........>
To: psnlist <psnlist@..............>
Sent: Mon, 31 Dec 2012 10:56
Subject: Re: Omnidirectional instrument

I'm just interested in first time of arrivalas well as distance and depth but 

not so muchabout axis. Possibly magnitude. 

I think the plane of arrivalcan be extracted from three or more sites with
timing which is both accurate and precise.
At least GPS quality.

Hi Goeff, 



    You don't need GPS quality timing. And a multitasking computer can't record it to 

anything like the accuracy of the received signal. They run on an interrupt cycling 

system several hundred times a second.

    P waves usually have a velocity of 6 to 8 km / sec depending on depth, so if you 

know the time correct to the nearest 1/10 of a second, this is good enough for our type 

of seismology. You can get this easily from WWVB signals - but NOT over the Internet. 



    Regards,



    Chris Chapman

      

    

I think the timing and everything are related to the A/D board type III
and not the computer running the WINSDR program. Every check I have made
using even WWV 10MHz has come out well.
I would agree with you If I were using my old hommade setup which
ran on a 16 bit program under MSDOS622 and run in a loop
doing things between taking samples at the tic counter rate.

You'll probably be happy to hear that I have returned to the
traditional negative input Opamp design and limited the spectrum
between 2Hz and 10 seconds. I found the noise at > 10seconds
to be unacceptable with 20seconds even dummy loaded.
I was unable to beat the noise back to acceptable levels.

When I redo the filter section I will lower the overall gain
and hopefully also the overall noise.

I expect possibly about 73Dbv overall gain in two sections
with the post amp/LPfilter being the second.

Regards & happy New year 2013,
geoff





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