15
Fig. 16: Connecting Ethernet cable
There are two Ethernet connectors on the GEM3D receiver. One is on the same side as the
power connectors and the other on the opposite side. The two connectors allows for network
connections to two other adjacent receivers, or one receiver and the PC Controller. These
connectors are reversible so it does not matter which side sends Ethernet to the PC Controller
and which side connects to adjacent receivers. Pushing the red “Test” button will power up the
GEM3D receiver if it has not already been power up with the NIB switch in “Enable Power Up”
mode.
D.
Electrodes and electrode cables:
Non-polarizing porous pot electrodes are recommended. The Geode EM3D does not use
electrode buffers since calibration is done real-time in the field. There are nine electrode
terminals as pictured in Fig. 10. The red terminals are considered to be positive by the
software. Black terminals are negative, and yellow terminals are shared between two adjacent
dipoles and can be either negative or positive, depend on which dipole. When a magnetic
sensor is connected to Hy (channel 6) the E dipole on channel 6 is disabled. When Hx on
channel 5 is connected the E-field connectors on channel 5 are disabled, and when mag Hz is
connected to CH4 the E-field channel four is disabled. Make sure all E-field dipole cables are on
the ground and not draped over plants, rocks, etc.. If the dipole cables are swaying or blowing
in a wind or breeze it will generate low-frequency EM noise.
E.
Magnetic coils and coil cables:
Magnetic coils should be buried to a depth of at least 30 cm to assure it is out of the range of
seismic vibration, which can generate low-frequency EM noise. The coils need to be properly
aligned and leveled. The Hy coil needs to be parallel to the Ey direction and the Hx coil needs to
be parallel to the Ex direction. If using an Hz coil it must be buried vertically.
