In a message dated 21/07/2005, dcrice@............ writes:

This is  not earthquake recording, this is exploration seismic. 
You will need  zero time from your shock source (a sledge hammer should be
adequate). The  best choice is a small, cheap crystal phonograph cartridge
taped near the  head connected to the second channel. You don't care about
absolute time,  just time relative to the impact, so forget GPS  timing.



I have used ordinary 13 mm piezo disks for the  hammer sensor, but you do 
need some sort of voltage limitation to  prevent input amplifier protection. The 
'glass break' sensors sold for  window protection work fine and are maybe less 
than 1/10 the price of a  phono cartridge. You can use biassed current 
differencing amplifiers to give a  ramped gain / time relationship to maintain the 
reflected signal strength.
 
    Regards,
 
    Chris Chapman






In a message dated 21/07/2005, dcrice@............ writes:
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  not earthquake recording, this is exploration seismic. 
You will n=
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  zero time from your shock source (a sledge hammer should be
adequate).=20=
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  best choice is a small, cheap crystal phonograph cartridge
taped near t=
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  head connected to the second channel. You don't care about
absolute tim=
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  just time relative to the impact, so forget GPS=20
timing.


    I have used ordinary 13 mm piezo disks for the=20
hammer sensor, but you do need some sort of voltage limitation to=20
prevent input amplifier protection. The 'glass break' sensors sold=
 for=20
window protection work fine and are maybe less than 1/10 the price of a=
=20
phono cartridge. You can use biassed current differencing amplifiers to give=
 a=20
ramped gain / time relationship to maintain the reflected signal strength.
 
    Regards,
 
    Chris Chapman