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Subelement L
Installation, Maintenance & Repair
Section 74
Indicating Meters
What is a 1/2 digit on a DMM?
• Smaller physical readout on the left side of the display.
Partial extended accuracy on lower part of the range.
• Smaller physical readout on the right side.
• Does not apply to DMMs.
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A 50 microampere meter movement has an internal resistance of 2,000 ohms. What applied voltage is required to indicate half-scale deflection?
• 0.01 volts
• 0.10 volts
• 0.005 volts.
0.05 volts.

50 microamps is full scale. Half scale would be 25 microamps.
Use Ohm's Law to calculate voltage:

V = (25/1000000 amps) x 2000 ohms = 0.05 volts

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What is the purpose of a series multiplier resistor used with a voltmeter?
It is used to increase the voltage-indicating range of the voltmeter.
• A multiplier resistor is not used with a voltmeter.
• It is used to decrease the voltage-indicating range of the voltmeter.
• It is used to increase the current-indicating range of an ammeter, not a voltmeter.
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What is the purpose of a shunt resistor used with an ammeter?
• A shunt resistor is not used with an ammeter.
• It is used to decrease the ampere indicating range of the ammeter.
It is used to increase the ampere indicating range of the ammeter.
• It is used to increase the voltage indicating range of the voltmeter, not the ammeter.
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What instrument is used to indicate high and low digital voltage states?
• Ohmmeter.
Logic probe.
• Megger.
• Signal strength meter.
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What instrument may be used to verify proper radio antenna functioning?
• Digital ohm meter.
• Hewlett-Packard frequency meter.
An SWR meter.

SWR = Standing Wave Ratio.

The Standing Wave Ratio is defined by wikipedia as the ratio of the partial standing wave's amplitude at an antinode (maximum) to the amplitude at a node (minimum) along the line.

Put in simpler terms, one of the most common ways to measure SWR is to use a directional wattmeter and measure the amount of power from the transmitter to the antenna ($P_f$ = Forward power) as well as the amount of power coming back from the antenna to the transmitter ($P_r$ = Reflected power).

The SWR can then be calculated using the formula:

$\text{SWR} = \frac{1+\sqrt{P_r\over P_f}}{1-\sqrt{P_r\over P_f}}$

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