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Subelement G4

AMATEUR RADIO PRACTICES

Section G4B

Tests and test equipment

What item of test equipment contains horizontal and vertical channel amplifiers?

  • An ohmmeter
  • A signal generator
  • An ammeter
  • Correct Answer
    An oscilloscope

(D). The oscilloscope is the item of test equipment which contains horizontal and vertical channel amplifiers. This allows the equipment to evaluate wave forms of RF signals, and observe changes to the signal with varying signal voltages by plotting values on the X (horizontal) and Y (vertical) axes over time.

For more info see Wikipedia: Oscilloscope

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Which of the following is an advantage of an oscilloscope versus a digital voltmeter?

  • An oscilloscope uses less power
  • Complex impedances can be easily measured
  • Greater precision
  • Correct Answer
    Complex waveforms can be measured

Both the digital voltmeter and oscilloscope can display different values of signal voltage, but complex waveforms can be hard to measure with a digital voltmeter—it's all just numbers. With a complex waveform often all you really want is to find a particular feature (like a peak), and that can be much easier by eyeballing it.

HINT: Oscilloscope is a complex word

"Oscilloscopes" show "Complex waves"

For more info see Wikipedia: Digital voltmeters, Oscilloscope

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Which of the following is the best instrument to use for checking the keying waveform of a CW transmitter?

  • Correct Answer
    An oscilloscope
  • A field strength meter
  • A sidetone monitor
  • A wavemeter

An Oscilloscope is used to measure oscillations in an electrical signal -- in other words, it shows you the waveform of the signal. The keying waveform of a CW transmitter is the visual representation of the tone transmitted by the transmitter when you press the key, which can be seen on the oscilloscope screen.

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What signal source is connected to the vertical input of an oscilloscope when checking the RF envelope pattern of a transmitted signal?

  • The local oscillator of the transmitter
  • An external RF oscillator
  • The transmitter balanced mixer output
  • Correct Answer
    The attenuated RF output of the transmitter

The attenuated RF output of the transmitter is connected to the vertical input of an oscilloscope when checking the RF envelope pattern of a transmitted signal. This allows you to check for signal distortions.

For more info see Wikipedia: Oscilloscope

**Memory tip: Output in the answer corresponds to Input in the question. ** KC3TGS

HINT: RF INPUT is in the question, RF OUTPUT is in the correct answer. KF4TYA

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Why do voltmeters have high input impedance?

  • It improves the frequency response
  • It allows for higher voltages to be safely measured
  • It improves the resolution of the readings
  • Correct Answer
    It decreases the loading on circuits being measured

Impedance is the measure of opposition to the flow of current. High input impedance is desired for a voltmeter because it limits, or decreases that loading on circuits being measured. Because of this the voltmeter only has to draw a very small amount of current from the circuit to be tested, and doesn't interfere with the normal flow and operation.

For more info see Wikipedia: Electrical impedance, Voltmeter

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What is an advantage of a digital multimeter as compared to an analog multimeter?

  • Better for measuring computer circuits
  • Less prone to overload
  • Correct Answer
    Higher precision
  • Faster response

(C). A digital voltmeter has an advantage over an analog meter because it has better precision for most uses. Digital voltmeters are easy to read if you are looking for a specific number level rather than trying to interpret the needle position on an analog scale. The analog meter may be more useful, however if you are looking for general up/down trends with being able to see the needle move in either direction, rather than focusing in on a specific value.

For more info see Wikipedia: Voltmeter

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What signals are used to conduct a two-tone test?

  • Two audio signals of the same frequency shifted 90 degrees
  • Correct Answer
    Two non-harmonically related audio signals
  • Two swept frequency tones
  • Two audio frequency range square wave signals of equal amplitude

A two-tone test uses two non-harmonically related audio signals to test the linearity of signal amplitude in an SSB transmission. The two tones of equal power are put into the microphone input and the waveforms are examined for linearity using an oscilloscope.

Hint: The two [tones] are "related".

Two-tone test

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What transmitter performance parameter does a two-tone test analyze?

  • Correct Answer
    Linearity
  • Percentage of suppression of the carrier and undesired sideband for SSB
  • Percentage of frequency modulation
  • Percentage of carrier phase shift

A two-tone test measures the linearity of an SSB signal.

A perfectly linear transmitter would produce those two tones—and only those two tones.

The more non-linear the transmitter, the more harmonics are generated, producing additional signal content at frequencies other than the two input tones.

The test itself consists of sending two tones that are not harmonically related into the transmitter. The tones are produced with equal power levels, so the only variable is frequency. The output can then be examined using an oscilloscope or spectroscope to see what other signals are being produced at other frequencies.

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When is an analog multimeter preferred to a digital multimeter?

  • When testing logic circuits
  • When high precision is desired
  • When measuring the frequency of an oscillator
  • Correct Answer
    When adjusting circuits for maximum or minimum values

When adjusting a circuit connected to an analog meter, you can see the indicator moving to a higher or lower reading - it's moving up or down.

When you're adjusting for a maximum or minimum value, you only have to look at whether it's moving up or down - you don't have to interpret a digital display of a number to get a sense of whether it's increasing or decreasing.

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Which of the following can be determined with a directional wattmeter?

  • Correct Answer
    Standing wave ratio
  • Antenna front-to-back ratio
  • RF interference
  • Radio wave propagation

A directional wattmeter is used to determine the standing wave ratio, which is the relationship between the forward and reflected power.

Its easy to determine the "Direction" of a wave if you are "Standing in the wave"

For more info see Wikipedia: Standing wave ratio, wattmeter

Oversimplification: Most SWR meters will tell you your forward watts and your reverse/reflected watts, in both directions.

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Which of the following must be connected to an antenna analyzer when it is being used for SWR measurements?

  • Receiver
  • Transmitter
  • Correct Answer
    Antenna and feed line
  • All these choices are correct

(C). Both the antenna and feed line must be connected to an antenna analyzer when it is being used for SWR (standing wave ratio) measurements. This device helps to measure the effeciency of your antenna setup.

For more info see Wikipedia: Standing Wave Ratio, Antenna analyzer

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What effect can strong signals from nearby transmitters have on an antenna analyzer?

  • Desensitization which can cause intermodulation products which interfere with impedance readings
  • Correct Answer
    Received power that interferes with SWR readings
  • Generation of harmonics which interfere with frequency readings
  • All these choices are correct

Antenna analyzers transmit a very weak signal and measures the SWR of that signal.

A strong signal from a nearby transmitter can enter the antenna under test and be reflected to the analyzer, confusing the SWR reading.

Hint: Super strong transmitter = SWR

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Which of the following can be measured with an antenna analyzer?

  • Front-to-back ratio of an antenna
  • Power output from a transmitter
  • Correct Answer
    Impedance of coaxial cable
  • Gain of a directional antenna

The antenna analyzer is a device that measures the input impedance of an antenna system.

The Standing Wave Ratio (SWR) is a measure of impedance mismatch, which is why an antenna analyzer is used to figure it out.

If you have an antenna with a known impedance, then you can use the antenna analyzer to figure out the impedance of an unknown or unmarked coaxial cable.

Notice that none of the distractors have anything to do with impedance.

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