Hi Jón,

I picked up two observations worthy of comment after looking at the gif's of the spikes, and reading your comments:

1.  They seem to increase in number after you have moved the seismometer.

2.  They all have some component below the zero line.  This could be the result of high pass filtering which applies a fraction of the initial pulse as an inverted result.  Of course there must be an initial pulse.

Is it possible that the spikes are coming from settling of the seismometer components, or of the seismometer base?  Are there springy components, such as stiff but flexible wires, that could be slowly reshaping over the course of several hours (or days) as they slowly move  or relax to a permanent configuration?   

The air shield surrounding the seismometer could also be the source of spikes if it settles over time.  

I doubt that the spikes are electrically generated.  If they were, they should be nearly equal for each channel (or be unique for each channel), and should not increase when you work with the equipment (or should dramatically increase as when there is a loose connection).  Capacitor  discharge events should be somewhat regular intervals, recognizing that the intervals could change with temperature or moisture, both environmentally controlled but easily observed and related to the appearance of spikes.

RFI (Radio Frequency Interference)should be observed in burst lasting several seconds or minutes.  I have seen noise that comes only on voice peaks (as from the voltage peaks on AM or SSB amateur radio transmission)  but even this occurs in a speech pattern.  Cell phone or transmission from business or emergency services vehicles should follow the typical burst speech pattern.

If the spikes truely increase after working near the seismometer, we should focus on why that should happen.

Best wishes,

Roger


----- Original Message ----- 
From: "Jón Frímann" 
To: 
Sent: Saturday, June 03, 2006 8:42 PM
Subject: RE: spike problem

(clipped for brevity)

This is the larger type of spikes.

http://www.simnet.is/jonfr500/earthquake/winquake/spike.hvt1z.gif

Here is a recording of the smaller spikes that happen after I did
connect the cat-5 cable directly to the geophone.

http://www.simnet.is/jonfr500/earthquake/winquake/smaller.spikes.hvt1z.psn.gif





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