PSN-L Email List Message

Subject: Re: arrogant university types, part 2
From: "GMV" gmvoeth@...........
Date: Sun, 22 Feb 2009 10:32:23 -0700

Thankyou Mr. Peters;

Wonderful response.

I do not normally deal with people on a personal level
I have lived in relative isolation for a very long time now
by personal choice and I know my communication abilities
are suffering due to this.
Technical people at the upper levels are very hard to
even see since they seem to be shrouded in national security
screens they themselves are not aware of.
You can be damned simply by studying them (national security) so beware.

I have heard of Mercer before but not as a technical college

I understand our entire university system is based on a GERMAN model,
yet, each college or university has a personality all its own.

Mercer is one of many I simply do not know.

Your verbosity is welcome by me since the English Language
is so terrible at describing things and requires much verbosity
to put a triangle exactly from one head into another.

Each and every academic discipline has its own vocabulary
which in my mind tends to isolate these various areas from
one another and make them all appear as being snobbish.

I KNOW that in this country somewhere is a vertical seismometer
built by military or corporation or nasa that would be a perfect standard
for amateurs to have but no one is sharing this knowledge of it.

I will continue to pick peoples brains simply because they have
filtered out most of the garbage floating around and can get
directly to what I need to know. Wading through mountainous
garbage of information is stealing my life since I have not the
life to learn everything.

Thanks for your response.

Best Regards;

----- Original Message ----- 
From: "Randall Peters" 
Sent: Sunday, February 22, 2009 7:55 AM
Subject: arrogant university types, part 2

(for reason of size, broken into two parts)

      About spurious signals other than aliases-I believe, Geoff,  you have also alluded to signals that can occur because of a 
'heterodyne' effect.  Please permit me to speak to this issue in some detail without (hopefully) appearing to be an arrogant ass.  I 
believe the salient features of this type of artifact are something I understand pretty well.  When the electronics has nonlinear 
characteristics (fundamental requirement for a mixer), then two signals interacting via this nonlinearity will generate sum and 
difference frequencies.  On a related issue, a single pure (monochromatic) signal will, when passing through the system that is 
nonlinear, produce harmonics.  (My PhD research was concerned with ultrasonic harmonic generation-similar to frequency doubling used 
to convert an invisible infrared laser (YAG) beam into a visible beam after passing through a KDP crystal).   The amount of 
harmonic(s) that are generated depends on the power.  For a single signal, the amount of harmonic content produced depends on the 
square of the power in that signal.  For two signals that mix, the sum/difference signals are proportional to the product of their 
individual powers.
     The 'verbosity' of the previous paragraph is to try and convince you that artifacts of the type that would be part of 
nonlinearity are not nearly so important for the list-serve readers as is the artifact of aliasing type.  And yes, you are 
absolutely correct-the standard procedure for eliminating an alias is to hardware filter out the offending signal before it can 
cause problems.  Again, however, I want to try and make the point (which I believe to be correct)-that the smaller the electronics 
package, the less likely is the probability of offending pickup signals to cause an alias.
      I want to also elaborate on the matter of what is required of the offending signal.  It must, as I mentioned before, be a 
persistent signal, such as 60-Hz pickup.  The coherence time (number of cycles through which the offending signal exists) is a very 
important issue, depending on its frequency compared to the frequency one studies.  These two must be related to one another as a 
ratio of commensurate integers for the alias to exist.
    Another of my comments that needs clarification.  You mention, Geoff, the possible ridiculous consequence of software 
'integration' (a discrete numerical approximation using software, operating by an iterative process).  You are correct that what 
comes out of the 'integral' may be useless.   The 'integrated' signal from the VolksMeter is used by me only as  a 'cue'.  I am 
interested in studying the 'pure' (raw) signals before, during, and after an earthquake, particularly teleseismic ones.  The 
helicord display of the integrated signal is a convenient way to improve the SNR for teleseismic viewing.  When I see something 
interesting in the integrated signal, I will then download only the non-integrated record.  I have never saved the integrated 
signals because so much information has been lost from them.
    More about the VolksMeter-my encouragement for some of you list-serve readers try and build something (especially a vertical 
instrument) using its operational principles-this was with the sure knowledge that many of you are much better skilled than myself 
(and probably every other 'professional' that I've met) when it comes to building both mechanical devices and also electronics. 
Larry Cochrane put together the first working prototype a couple of years ago.  Hearing what was needed (both mechanical and 
electronic) on a Saturday, he proceeded to have one both built and operational on the web the following Monday!  I wrote and asked, 
"do you routinely 'walk on water'; if so I want to come out and watch sometime".
    You could build such an instrument 'on a shoestring'.  The mechanical parts would be 'a breeze' for many of you and I'll bet 
that you will be surprised at how low the cost is for the electronics.   I want to see what might develop, because my efforts have 
'only scratched the surface' of possibilities.


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