On 2012-11-10 3:14, Brett Nordgren wrote:
> Geoff:
>
> What I think you were saying is that a geophone makes a poor detector
> for distant quakes.  Quite true.
>
> If you turn up the gain high enough to see distant quakes, the local
> ground noise plus the instrument noise, is overwhelming.  When you
> reduce the sensitivity enough to make the noise look reasonable you will
> only see nearby quakes.  Dave's geophone setup which goes from 0.5Hz to
> perhaps 50 Hz, gives beautiful traces for the small quakes that often
> occur within 100 km of LA.  Their traces closely match what the
> broadbands see.
>
> Rarely, there will be a teleseism that is large enough for its p-wave to
> show up on the geophone above the noise, but they have to be pretty big
> and don't happen often.
>
> Even the commercial geophone-based sensors are quite noisy when you look
> at their specs.
>
> Geophone sensors are a great tool for recording nearby quakes.
>
> Regards,
> Brett
>
>
>
> At 10:31 AM 11/9/2012, you wrote:
>> On 11/9/2012 6:30 AM, Bob Smither wrote:
>>>
>>> On Fri, 2012-11-09 at 06:10 -0800, GMVoeth GM wrote:
>>>> Hello PSN,
>>>>
>>>> I know with a velocity sensor the voltage increases with frequency
>>>> after
>>>> F0 if given the same
>>>> vertical motion amplitude. This seems to be because as the frequency
>>>> increases
>>>> so does the velocity and thus, the voltage output.
>>>>
>>>> This means to me the energy also increases as the square of the
>>>> velocity.
>>>> So like, double the velocity, quadruple the energy.
>>>>
>>>> What i would like to do is: filter at f0 (1.0Hz) so that given
>>>> a steady shake amplitude (sine wave) but incresing frequency
>>>> that the voltage will remain constant.
>>>>
>>>> Now I understand this may not be possible.
>>>
>>> I think it is.  A simple RC low pass filter (R from signal to C, C to
>>> ground, output at junction of R and C) gives:
>>>
>>>    T(S) = 1 / (R*C*S + 1)
>>>
>>> Above w = 1/(R*C) this is
>>>
>>>    T(S) ~ 1 / (R*C*S)
>>>
>>> exactly what you need to reduce gain proportional to frequency.
>>>
>>> For your example, w = 2*pi*1Hz = 1/RC so C = 1ufd, R = 160K should work.
>>
>> I find this interesting.
>>
>> I have eliminated filters except for a single HPF n=1 at like 100seconds
>> and am looking at pure noise.
>>
>> At 8AM MST today I get occasional over driving (jamming) of my
>> preamplifier with no filtering.
>>
>> I need this level of amplification to see the smaller seismic signals.
>>
>> If I apply n=2 LPF at 1.0Hz using winquake I get the best flattening
>> of the noise baseline above 1.0Hz. Noise is human vehicular related.
>>
>> It is an absolute must for me to apply n=2 at 1.0 Hz to prevent
>> jamming by vehicular and other noise.
>>
>> Does this mean there is a problem with my geophone
>> or is vehicular noise increasing with frequency like n=1
>> to add to the velocity profile of the geophone ?
>>
>> None of this is speaking of Alizing problems.
>>
>> this is an extremely noisy town for vehicular activity.
>> (Apache Junction AZ USA)
>>
>> Would it be best to stop recording during the day
>> or best to heavily filter to keep the system from being
>> jammed. Heavy filtering terribly affects the resulting
>> waveforms ?
>>
>> Regards,
>> geoff
>>
>>
>>
>>
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>
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Thanks to all who have responded,
I have decided to go with a negative input
Preamp with about x600 DC gain and an N=1 LPF
about 3 Hz right at the preamp.
I will place on my web site at some future
date an updated schematic.
I have chosen this over heavy hardware filtering
because with heavy filtering the
waveform seems horribly distorted in phase
and shape. The geophone is HS10-1 1Hz and the
resistance vary greatly over the year.
In winter it can be near 400Ohms and in
summer about 440 or 450. Maybe someone
can point me to a formula for copper wire
which converts temp to resistance.
I have been playing around since 1994 with
various circuits watching the noise level
increase as the area becomes populated.
I know where all the oil gas and coal is going,
back into the ground as energy.
The single best way to get a proper response
is with a 5 second geophone with like 3V/(in/sec)
or better generator constant and vertical and small
enough to bury in the ground. Hopefully, no greater
than 500 OHMS resistance at STP.
I have seen nothing better than Larry's hardware
to keep great time keeping and show everything. I think
he might one day be a standard for Amateurs.
just need that 5 second geophone at a reasonable cost.
I have seen no better geophone than the SPZ HS10-1.
But it is horribly expensive as a new device.
Possibly you will not find one today.
I was lucky to find the used one from Larry.

Prosit, Cheers, AufWiedersehen;
geoff [GVA]


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