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121Appendix B Theory of Operation
B
Theory of Operation
Overall Functional Description
The meter is a portable, battery-operated instrument that forms
a complete RF Radiation Survey System when used with an
interconnected Narda 8700 Series probe. Optionally, the
system may employ a fiber optic transmitter and cable between
the probe and meter. The survey system is designed to detect
electromagnetic fields and to display the field level on the
meter’s Liquid Crystal Display (LCD). The probe detects the
electromagnetic radiation and transmits a DC signal to the
meter. The meter processes the signal from the probe for
viewing on the LCD screen. The meter displays the field levels
in various units of measure dependent on the field component
detected and the characteristics of the probe used.
Probe Functional Description
The probe senses the electromagnetic fields and develops a
signal for transmission to the meter. The probe has an isotropic
sensing pattern so that the radiation may be sensed from any
direction, except through the handle. Detectors in the probe
sense the electromagnetic radiation present and apply signals
to preamplifiers U1 and/or U2 located within the probe.
Preamplifiers U1 and U2 amplify the signals from the detectors
and route them to the meter via connector P1.
Model 8718B Meter Functional Description
The meter receives the signal(s) from the probe, processes the
signal(s) and provides a visual display of the levels detected.
The signal(s) received from the probe at PROBE connector J1 is
routed to amplifier U2. Amplifier U2 amplifies the signal(s) from
the probe and generates a signal to drive the A/D converter U3.
The output of the A/D converter is routed to microprocessor U5
that drives the LCD.