Unit 7. General Purpose Test Equipment Instruments Flashcards
- Fluke 8025A Multimeter
1. Which control do you use to select the meter’s different measurement functions?
The rotary switch.
List the four types of information presented in the multimeter’s display section.
(1) Digital display.
(2) Visual annunciators.
(3) Analog bar graph.
(4) Range indicator.
Which information in the display section shows the absolute value of the input?
Analog bar graph.
Describe the function of the range push button.
The range push button lets you manually select the measurement range.
What is the purpose of the touch-hold push button?
The touch-hold push button locks the measurement into the display for viewing and automatically updates
the display when you take a new measurement.
List the multimeter’s four input jacks.
(1) Amperes
(2) Milliamps/microamps.
(3) V olts/ohms/diode.
(4) Common.
When does the 8025A perform a power-up self-test?
- When you move the rotary switch to any position from the OFF position
- Using the Fluke 8025A Multimeter
1. What two ranges of DC voltages can you measure using the 8025A multimeter?
- What is the maximum amount of continuous AC current you can measure with the multimeter?
10 amps.
- When using the Fluke 8025A, how do you know you’re in the resistance measurement function?
The ohms annunciator is showing in the display.
- How do you determine if you’re testing a “good” diode with the 8025A?
Placing the leads across a “good” diode produces “OL” in the display while reversing the leads produces a continuous audible tone.
- Oscilloscope basics
1. What type of display does the oscilloscope present?
Amplitude vs time.
- On which axis of an oscilloscope is voltage, time, and depth information presented?
Voltage = Y axis, time = X axis, and depth = Z axis.
- What is the purpose of the delay line at the input of the vertical amplifier?
It allows the sweep generator circuitry time to start a sweep before the signal reaches the cathode ray tube vertical deflection plates. This enables you to view the leading edge of the signal waveform.
- What position of the input coupling switch is used to view digital-type or square wave signals?
DC coupling.
- Basic oscilloscope probe considerations
1. What is the basic purpose of the oscilloscope probe?
To provide isolation for scope inputs and prevent circuit loading.
- List four types of probes.
(1) Passive.
(2) Passive divider.
(3) Active (field effect transistor).
Amperes.
(4) Current probes.
- What is the typical input impedance of most oscilloscopes?
One megaohm shunted by 20 pF of capacitance.
- When making an amplitude measurement and the source impedance is unknown, greatest accuracy is achieved when the probe’s Zin is what?
Highest (maximum).
- Why do we test ground?
1. Why do we test ground?
To verify the ground-resistance specification that the ground rod or grid must meet.
- What test equipment is used to identify a poor ground?
Earth ground tester.
- Basics of earth ground testing
1. What is another name for the fall of potential test method?
The three-point method.
- What is each point of contact called in the fall of potential testing method?
(1) The test ground.
(2) V oltage probe.
(3) Current probe.
- At what distance represents the closest value to the theoretical true resistance measurement?
61.8 percent of the total distance.
- How are the earth stakes placed in the soil?
In a direct line away from the earth electrode.
- Which law is used to calculate the resistance of the earth electrode automatically with the earth ground tester?
Ohm’s Law.
- Where are the probes placed in order to achieve the highest degree of accuracy?
Placed outside the sphere of influence of the ground electrode under test and the auxiliary earth.
- What ground resistance value is recommended by the NFPA and IEEE?
5 ohms or less.
7–4. Radio Frequency Signal Generators
- Characteristics and applications of a radio frequency signal generator
- What is the frequency range of the HP 8640B RF signal generator?
500 kHz to 512 MHz (450 kHz to 550 MHz with over-range).
- What extends the HP 8640B range from 20 Hz to UHFs?
A variable audio oscillator can extend the output range of the generator down to 20 Hz and a doubler can extend it to 11,000 MHz.
- What is the function of the oscillator section?
To produce a signal that can be set accurately in frequency at any point within the range of the generator.
- What is the function of the modulator?
To produce an audio modulating signal to superimpose on the RF signal produced in the oscillator.
- What types of modulated signals are possible with the RF generator?
Either sine waves, square waves, or pulses of varying duration.
- What components are generally part of the RF signal generator output circuit, and what are their functions?
A calibrated attenuator and an output level meter. The attenuator lets you select the amount of output required. The output level meter provides an indication and permits control of the generator output voltage.
- List some applications of the RF generator.
1- Verify transmission within designated frequency ranges by comparing transmitter outputs with known radio frequencies.
2- Align a receiver by injecting the system with range-standard modulated radio frequency.
3- Check transmission lines and antenna systems for proper operation.
- Defining the terms decibel and dBm
1. The decibel is part of what larger unit of measure?
Bel.
- A power ratio of 10,000:1 can be represented by how many bels?
Four.
- What’s the most commonly used industry standard power reference level?
The 1-milliwatt standard.
- How is the answer to question number 3 expressed?
As decibels referenced to a 1-milliwatt standard or dBm.
- Rewrite these sentences so they use the term dB correctly.
(a) This TWT has 25 dB of output power.
(b) The final amp is pumping out a 30 dB package.
(a) This TWT has a power gain of 25 dB.
(b) The final amp is pumping out a package that’s 30 dB more than its input.
- What will every 3 dB increase in gain do to the power level?
Roughly double it.
- How many dB of gain does an amplifier have if there are 10 watts in and 80 watts out?
There’s a gain of 9 dB.
- You have installed an in-line 3 dB attenuator between a power source and the power sensor of a power meter. How will this affect the power level displayed by the power meter?
It will cut it in half.
- What two power characteristics are reflected by the term dBm?
Gain and power level.
- How do the terms dB and dBm differ?
Because dBm is always referenced to a 1-milliwatt standard, it can be used to reflect a power level, in addition to gain or loss. The term dB can’t reflect a power level; instead, it can only reflect gain or loss because it’s purely a ratio.
- How much more power is available at 6 dBm than at 3 dBm?
Twice as much.
- What power levels are indicated by these measurements?
(a) 3 dBm.
(b) 9 dBm.
(c) 12 dBm.
(d) 36 dBm.
(a) 2mW.
(b) 8 mW.
(c) 16mW.
(d) 4,096 mW (approx 4.1 watts).
- Power meter—features and controls
1. List at least three of the units that can be displayed by the HP 436A power meter.
(1) Watts (W).
(2) Milliwatts (mW).
(3) Microwatts (μW).
(4) Nanowatts (nW).
(5) Decibels referenced to a 1-milliwatt standard (dBm).
(6) Relative decibels (dB REL).
- Briefly explain how to use the relative power measurement mode for frequency response testing.
After the input is connected, press dB(REF) to lock in this frequency level as the reference, then tune the transmitter to other frequencies and observe any changes up or down in the power level.
- Match the power meter characteristics in column A with the HP 436A features in column B. Each feature in column B can be used once, more than once, or not at all.
Column A
F (1) For receiving commands from a computer.
B (2) Determines the frequency range.
A (3) Ideal for monitoring peaking power.
C (4) Provides hands-free operation.
D (5) Press SENSOR ZERO to activate.
E (6) Can be used to stabilize the power source.
B (7) Determines power measurement range.
G (8) Provides a stable 1.00m@, 50 MHz output.
E (9) Output can be used to print graphs.
Column B
a. Auxiliary meter.
b. Power sensor.
c. Auto-range.
d. Auto zero.
e. Recorder output.
f. Interface connector.
g. Calibrator accuracy.
h. Radio frequency blanking
output.
- Wattmeter—features and controls
1. What is the 4391M RF Power Analyst designed to measure?
The power flow, load mismatch, and AM in 50 ohm coaxial transmission lines.
- What are the two switches on the front panel of the instrument used for?
Two switches on the front panel of the instrument are set by the user to correspond to the power range of the forward element.
- If only the forward element is used, what is filled in the other socket?
With a dust plug or a higher power element.
- Why are the elements clamped into place by the hold-down catches on the face of the line section?
These catches must be used to avoid error due to the element not contacting the bottom or seating plane of the socket.
- When powered up, which mode is the 4391M wattmeter default?
The forward CW power mode.
- When reading forward power, what will be displayed if the applied power exceeds 120 percent of the range?
Two right facing arrowheads will be displayed.
- Where is the reflected CW reading taken?
From the element in the socket marked “reflected.”
- Between what power ranges will a SWR be displayed?
Between 10 and 120 percent of the full scale and the average reflected power is less than 120 percent of the reflected element range.
- What is the difference in readings for CW and PEP?
Readings are displayed directly as peak power in PEP. To formulate CW power, the wattmeter measures peak and minimum square root of power and combines them.
- How is over-modulation displayed on the wattmeter?
Over-modulation will be indicated as 99.9 percent.
- What must be added to the dBm reading when the range is in kilowatts?
30 must be added to all dBm readings when the range is in kilowatts.
- When measuring return loss, what does a reading of 21.6 indicate?
The measurement of return loss reading of 21.6 indicates that reflected power is 21.6 dB down from forward power.
- In order to recall the maximum reading, what key do you press?
To recall the maximum reading, hold the MAX key down.
- How do you clear the minimum and maximum register?
To clear the minimum and maximum register, the mode key must be pressed again or a new key selected.
- Which mode is useful for making adjustments to optimize any of the parameters which the wattmeter measures?
Peaking aid.
- AM–48, Personal Transmission Test Set
1. What is the output frequency and audio level range of the AM
200 to 20 kHz at levels from -50 to +10 dBm.
- What is the measurement range for audio level and frequency in the AM
-65 to +10.9 dBm (absolute or relative) at frequencies from 0 to 19,999 Hz.
- How is the AM
Four AA 1.5-volt alkaline or NiCad rechargeable batteries. An AC adapter is also provided to connect to 115 VAC.
- AM
(1) Sets to view MEASUREMENT mode in absolute reference
(2) Sets to view MEASUREMENT mode in relative reference.
(3) Sets to view the SEND mode.
- How many test set-ups can be saved to the AM
10.
- What does pressing on the “Speaker Control” rocker switch enable the technician to do?
It mutes the speaker and connects the internal microphone to allow “talking” over the send pair.
- Functions of a spectrum analyzer
1. What is a major difference between the oscilloscope and the spectrum analyzer?
The oscilloscope displays frequency information in the time domain, whereas, the spectrum analyzer displays frequency information in the frequency domain.
- Describe how the spectrum analyzer displays information in the frequency domain.
By complex signals (i.e., signals composed of more than one frequency) that are separated into their frequency components, and the power level of each frequency is displayed.
- What functions does the spectrum analyzer perform?
(1) Locate and identify signals over a wide frequency spectrum.
(2) Magnify parts of the spectrum for detailed analysis with stable, calibrated sweeps and resolution. (3) Minimize display clutter for spurious responses within itself.
(4) Furnish wide dynamic range and flat frequency response.
- What advantage does the spectrum analyzer’s sensitivity and wide dynamic range provide?
A way to measure low-level modulation.
- List some uses of the spectrum analyzer.
(1) Measure AM, FM, and pulsed radio frequency.
(2) Measure long- and short-term frequency stability.
(3) Measure parameters such as subcarrier oscillator outputs, channels of complex signals.
(4) Measure frequency drift during system warm-up.
- Functions of an electronic counter
1. What is the frequency range of an electronic frequency counter?
Low audio frequencies up to 550 MHz. Some methods are available to extend the frequency range of counters to more than 20 GHz
- What provides the time reference for the precise timing and where does this function take place?
A quartz-crystal oscillator inside the counter.
- Portable instrument landing system receiver
1. What components make up the PIR?
The PIR electronics, LOC/GS antenna assemblies, a battery assembly, and a 12-volt DC power supply.
- What items are found in the PIR accessory kit?
A carrying case, antennas, cables, adapters, monopod support, and power supply.
- What is the configuration of the digital portion of the PIR?
Five seven-segment digits with decimal points between segments.
- When is a 30 dB attenuator placed in-line with the RF input of a PIR?
Levels known to be greater than 10 dBm.
- Vector voltmeter
1. What primary things must you remember when using the VVM?
Do not exceed the maximum input voltage rating and handle the probes with care.
- What is the phase finder?
Overrides PHASE RANGE and PHASE METER OFFSET to select the +/-180 degree phase range and zero offset; used to find phase angle without changing settings of controls.
- Care of test measurement and diagnostic equipment
1. Techniques for cleaning electronic equipment are found in which TO?
TO 00-25-234, General Shop Practice Requirements for the Repair, Maintenance, and Test of Electrical Equipment.
- Care of TMDE is in which technical order?
TO 00-20-14, Air Force Metrology and Calibration Program.
Column A
A (1) Measures total number of input cycles over a period of time.
B (2) The average bit-to-bit time of the input signal in a digital system. (3) Measures the time between two points of a common event.
C (4) Provides a divided version of the input frequency.
D (5) Counts the number of bits in a pulse train.
A (6) Measures harmonically related signals.
Column B
a. Ratio.
b. Period.
c. Scaling.
d. Totalize.
e. Frequency.
f. Time interval.
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