LCD Display D1

Keypad S1

Battery B1

The LCD is a self-contained display and meter circuit assembly. The display has four lines with twenty characters per line. Each character is a 5 x 7 dot matrix. The display is backlit for improved visibility under low light conditions. It connects directly to PCB A1.

The keypad has 22 keys. It is shielded in aluminum and connects directly to PCB A1.

The battery pack is a custom package consisting of six individual NiCd cells. It has a rated output of 7.2 volts with a capacity of 7.2 Ah. The battery pack contains an over current protection device. It connects directly to PCB A1.

Probe Designs

The probes used with the Model 8718B meter measure either the electric field or the magnetic field. Some have a flat frequency response, others have a shaped frequency response (see Chapter 3, Probe Selection). All 8700 series probes have square law characteristics that provide an accurate summation of field levels present from multiple frequency sources. All probes are internally coated with a thin film, high resistive coating. The film is on the order of 0.5 M per square inch and provides a shield against electrostatic charges. All 8700 series probes utilize a preamplifier in the handle to amplify the detected signals from the sensors. This eliminates probe-to-meter cable modulation. The probe amplifiers are connected to the probe elements by inflexible monolithic resistive leads. This prevents cable modulation from affecting the signal derived from the elements. Each instrumentation amplifier consists of three distinct sections: two analog and one digital.

Communications The 876xD series probes operate from 300 kHz to 3 GHz. They

Band Electric use three sensors supported along mutually orthogonal axes.

Field Probes Each sensor consists of a dipole-diode combination. The dipoles are approximately 8 cm in length. The broad beam width is achieved through the capacitive divider effect of the dipole-diode combination. Some linearity correction is provided for field levels that approach full scale. A patented circuit design maintains RMS detection over the entire dynamic range of the probe.

Appendix B Theory of Operation

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