User's Manual

Geophysical Survey Systems, Inc. Model 3101A Series Antennas
System Settings and User Notes
Signal Position
Place the antenna on the ground and use the Automatic Signal Position selection. The system
will servo and place the direct coupling pulse at the top of the time range window.
To test that you have the correct position, raise the antenna off the ground and you will observe
on your system that the antenna transmit pulse (direct wave) will separate from the reflection
from the ground. The higher that you raise the antenna, the further apart will be the two pulses.
Newer control units such as the SIR-3000 and the SIR-20 have advanced algorithms to locate the
surface position. If you would like to assure that the direct coupling pulse (time zero) is recorded,
the user should place the Signal Position Servo in the manual mode. The signal should then be
moved down in the time range window until the entire surface pulse is visible and there is some
‘dead time’ or flat trace visible above the direct coupling pulse in the time range window. If you
are using your 3101A with the SIR-3000, it will be necessary to set the SURFACE% to zero in
order to check the signal position. Please consult the SIR-3000 User’s Manual for additional
instructions on this point.
Gain Check
The surface pulse should be about 2/3 the width of the screen. If it is greater, reduce the Gains
manually. If the signal appears too small, you can manually increase the Gains, but the first gain
point should never exceed 10dB; the last gain point should not exceed 65dB.
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