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Figure 6-40.Common probe tips
BASIC FUNCTIONAL DESCRIPTION

Neets Module 16-Introduction to Test Equipment
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6-37 Since the probe resistor is in series, the oscilloscope input resistance is 10 megohms when the probe is used. Thus, using the attenuator probe with the oscilloscope causes less circuit loading than using a 1- to-1 probe. Before using an attenuator probe for measurement of high-frequency signals or for fast-rising waveforms, you must adjust the probe compensating capacitor (C1) according to instructions in the applicable technical manual. Some probes will have an IMPEDANCE EQUALIZER in the end of the cable that attaches to the oscilloscope. The impedance equalizer, when adjusted according to manufacturer’s instructions, assures proper impedance matching between the probe and oscilloscope. An improperly adjusted impedance equalizer will result in erroneous measurements, especially when you are measuring high frequencies or fast-rising signals. More information on oscilloscope hook-ups can be found in Electronics Information Maintenance Books (EIMB), Test Methods and Practices. Special current probes have been designed to use the electromagnetic fields produced by a current as it travels through a conductor. This type of probe is clamped around a conductor without disconnecting it from the circuit. The current probe is electrically insulated from the conductor, but the magnetic fields about the conductor induce a potential in the current probe that is proportional to the current through the conductor. Thus, the vertical deflection of the oscilloscope display will be directly proportional to the current through the conductor. SPECTRUM ANALYZER The spectrum analyzer is used to examine the frequency spectrum of radar transmissions, local oscillators, test sets, and any other equipment operating within its testable frequency range. With experience, you will be able to determine definite areas of malfunctioning components within equipment. Successful spectrum analysis depends on the proper operation of a spectrum analyzer and your ability to correctly interpret the displayed frequencies. Although there are many types of spectrum analyzers, we will use the Tektronix, Model 492 for our discussion. The spectrum analyzer accepts an electrical input signal and displays the frequency and amplitude of the signal on a CRT. On the vertical, or Y, axis, the amplitude is plotted. The frequency would then be found on the horizontal, or X, axis. The overall pattern of this display (figure 6-42) indicates the proportion of power present at the various frequencies within the spectrum (fundamental frequency with sideband frequencies).






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