ULF HARDWARE DESCRIPTION

The Basic ULF system consists of :
        (1) one,  3 foot long,  ULF antenna module,  with built-in high-gain
              low-noise amplifier. weight,  about 5 pounds.
        (2) one KEITHLEY DAS4 Analog to Digital card         ( ref  #1 )
        (3) one 60 cycle power-line synchronization circuit  ( ref  #2 )
        (4) a dedicated IBM compatible PC, with color monitor
        (5) the logging and viewing software
        (6) cabling to put it together.

Options include
        (1) ULF antennas for two other axis.
        (2) one vertical electrostatic antenna and amplifier
        (3) one vertical axis seismometer and amplifier
        (4) one vertical axis broad-band RF antenna and amplifier

Hardware descriptions and Circuit diagrams are on the  ftp site. 

The amplifiers, shown in Geo-Monitor(3) over the last few years have an 
essentially  "flat" response over the ULF frequency range. ULFLOG will 
work well with any of these designs, so long as the amplifier response 
is falling rapidly at 25 Hz and has a 60 Hz notch filter.  This response 
curve is important because any amplifier output  signal above 30 Hz will 
"fold-back"  or  "alias"  into the desired data, becoming 
indistinguishable from "real" data and creating "phantom" responses.   
For example, a 55 Hz  signal will be indistinguishable from  a 5 Hz 
signal.

(1) KEITHLEY DAS-4 @ $250 ... 8 bits @ 4 Khz ... 
    clones are available at about $150. 

(2) sync module ... see the ftp site
(3) Geo Monitor
    65 Washington Street #400
    Santa Clara, California  95850   (408-749-6770 )