Hello Bob;

I guess I am no scientist because the basic
idea seems so simple to me that the signal to noise
ratio can be somewhat arbitrary in your selection
of reference points.

You pick a signal level of interest
and make sure your S/N ratio is such
you will actually see the signal of interest.

Any signal with like 6dbv X2 above the noise
should be visible. One that is 120db
is a million times the noise.

It all depends upon what noise you mean
and to me that is overall "S" noise.
White Noise. Like on an "S" meter.

As any bubblehead should know ( Sub-Sailor )
S/N is one of the sinle most important facets
of any sensor device.

I am amazed that an NMR machine can
rattle a mole of atoms in a strong
magnetic gradient and listen
to them ring With various frequencies
in response.

They must have a receiver unlike anything
I am familiar with.

I would start by looking at the USGS noise levels
then figure out what S/N ratio needs to be
before designing a serious device.
The place i live in here is so terribly
noisy I need to filter right at the
preamp to keep my electronics from
being jammed by higher vehicular frequencies.

It probably would do me little good
to invest in high class low noise
amplifiers at my current location.

The overall noise of your system
needs to be lower than the grass.
To the point of diminishing returns.
The grass being the noise in the ground
at whatever bandwidth during a quiet
sunday morning like 3am local time.

Most people do not build their own
devices and do not concern themselves
with this thought.
There are many types of noise but the only
one of interest is the overall results.
I cant wait until Universal Entropy Reaches Maximum
That will be the quietist time of all.

Regards
geoff

----- Original Message ----- 
From: "Bob Hancock" 
To: 
Sent: Saturday, November 03, 2007 5:06 PM
Subject: Re: Signal To Noise Ratio


Hi Geoff -

Unfortunately, my knowledge of electronics is less than stellar.  I am
working at understanding concepts of seismology.  As for
electronics.....well, I'll leave that for someone else.  I was hoping to
find an answer that would allow me to apply the SNR numbers I see to the
practical side of seismology.  I understand the simple concept of an
amplifier (boosting a signal), but unfortunately, I have no working
knowledge of their innards or how the individual parts work by themselves
and in concert with each other.

Bob H



On 11/3/07 4:50 PM, "Geoff"  wrote:

> Hello Bob;
>
> Have you ever heard of a low noise
> GaAs op amp that is designed to work
> like a op177G (typical opamp) or ??
>
> Signal to noise ratio should be easily found
> in google I think it simply is like
> Expectided MDL signal power / Ubiquitous Noise Power
> The higher the ratio the better the whatever.
> Possibly expressed in db.
> For power thats 10Log(Sig/Noi).
> The noise would be the reference point.
> If you can get a 120db (coopers)
> I think youd be in fat city.
> The higher the overall s/n ratio
> the smaller signals they can see.
> Like someone sneezing next door.
>
> :-)
> geoff
>
> ----- Original Message -----
> From: "Bob Hancock" 
> To: "PSN" 
> Sent: Saturday, November 03, 2007 1:16 PM
> Subject: Signal To Noise Ratio
>
>
> When downloading events through IRIS ­ Wilber II, I noticed that they listed
> the signal to noise ratio.  Most of the time the number was ­1; however,
> there were other numbers listed.  I have some questions and hopefully
> someone can answer them.
>
>
> 1.  What is the significance of signal to noise ratio when looking at
> earthquakes?
>
> 2.  How is signal to noise ratio computed?
>
> 3.  What are the ideal numbers to look for and at what point does the data
> become unusable?
>
> Thanks
>
> Bob Hancock
>
>
>
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