Hi all,

Reaching across the desk to my ham radio stuff, we have been using 
spectral analysis for very low speed CW on experimental LF 
communications/beacons.  They have to resolve down to the sub-hertz 
region.  A popular program, ARGO, that is free and runs on the PC is 
available for download at

http://www.weaksignals.com/

Look at the ARGO page.  Alberto, I2PHD and Vittorio, IK2CZL, have done a 
lot of work to make this software run on most PCs without a lot of 
special sound cards etc. The seismo data may have to be modulated with 
an audio tone to get the data within the passband of the sound card.  It 
could prove useful for examining microseisms.

Frank K0BRA

Larry Conklin wrote:

> Jack,
>
> I would love to hear more about this idea.  I worked for many years in 
> sonar development, so I have a pretty good idea
> of the merits of the technique.  I don't have Matlab or anything 
> comparable around here to try it.  Sounds like a good
> software project.
>
> Larry Conklin
> Liverpool, NY
>
> Jack Ivey wrote:
>
>> There's a different way to look at seismic records that is particularly
>> interesting for microseisms.  For a long time I've been using the 
>> specgram function of Matlab to look at both microseisms and quakes.  
>> Specgram essentially divides the signal record into blocks of time 
>> and performs an FFT on each block.  It then displays the FFT 
>> amplitude as a gray scale (or other color map).  The Y axis of the 
>> display is increasing frequency, the X-axis is time, and brightness 
>> of each pixel corresponds to the amplitude of the signal at that time 
>> and frequency.
>> Essentially you get an image showing how each frequency component 
>> changes
>> with time. 
>
>
Snip snip

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