A digital oscilloscope operates by digitizing the signal with an analog-to-digital converter (ADC) before processing and displaying the result. An ADC is limited in the range of frequencies that can accurately be converted by what is known as the Nyquist frequency. This is typically 1/2 of the sampling rate of the ADC.

See http://en.wikipedia.org/wiki/Nyquist_frequency

Hint: There are limits on how many samples you can get.

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Envision an oscilloscope with a line going from left to right. The line going from left to right represents increments of frequencies. The line going up and down represents the strength (amplitude) of the sum of the signals present at the frequency. Most frequencies appear as spikes in compressed mode. Expand the line out, and the spikes appear as sharp mountains. This tool is useful in viewing frequencies close to the target frequency, bandwidths and RF shielding assessments.

Here is an example of a "spectrum scope", which is a type of spectrum analyzer display, along with the "waterfall display" under it: https://blog.icomamerica.com/wp-content/uploads/2020/04/VHFSpectrum_01.png

More info here: https://en.wikipedia.org/wiki/Spectrum_analyzer

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A spectrum analyzer displays the strength of a signal, and signals above and below the signal's frequency. Since spurious signals and/or intermodulation distortion products appear above and below a SSB signals frequency, the spectrum analyzer is a useful test instrument for displaying these.

You can adjust the vertical and horizontal scales on a spectrum analyzer - the vertical scale is the signal strength in Decibels, and the horizontal scale is the width of the spectrum being displayed.

Hint - The question asks about "spurious" signals and the answer is "spectrum" analyzer. Both words start with "sp".

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The probe is adjusted until the horizontal flats of a square wave are as flat as possible.

This adjustment is equivalent to making the probe have uniform attenuation over the range of frequencies to be measured. In passive probes this adjustment is usually a small adjustable capacitor.

Silly trick: Cubes are three dimensional, but squares are as flat as possible!

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A prescaler is an electronic counting circuit used to reduce a high frequency electrical signal to a lower frequency by integer division. The prescaler takes the basic timer clock frequency and divides it by some value before feeding it to the timer, according to how the prescaler register(s) are configured.

Mnemonic: think of -divisions- on a -scale-.

Silly Hint: the pre-schooler's (prescaler) voice has to be reduced to an acceptable range designated by the teacher (counter.)

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Nyquist's sampling theorem states that the highest frequency that can be unambiguously reconstructed is at half the sampling rate, and above this, aliasing occurs.

If one should sample at 20MHz, signals of up to 10MHz can be reconstructed.

For example, if one supplied a 20,000,000 Hz signal to this oscilloscope, the oscilloscope would sample the same value every cycle, and the signal would totally disappear. If one instead supplied a 20,000,001Hz signal, the signal would drift in phase with the sampling at 1Hz, and a false 1Hz sine wave would be displayed.

Generally, an oscilloscope sampling at 20MHz will have filters to reject signals above 10MHz for this reason.

Memory Aid: When you read “aliasing” in the question, think of an alias as a false name. This will drive you toward the correct answer choice.

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An antenna analyzer has its own built in signal source.

Hint: "Antenna analyzer" and "SWR" are in both the question and answer.

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SWR or Standing Wave Ratio is a measure of the relative impedance of an antenna to the expected impedance by the transmitter. This is measured by an antenna analyzer or a SWR meter.

A spectrum analyzer measures signal amplitude in the frequency domain.

A Q meter measures the efficiency of a tuned circuit.

An Ohm meter measures the resistance of a circuit.

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The probe tip and ground of an oscilloscope acts like a sensitive antenna loop. The bigger the loop the more undesired signals or noise it will pick up. Also, the inductance of the ground wire increases with length, which can distort high-frequency signals. So, keep it short as possible.

Hint: Practice, possible, probe.

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A logic analyzer is a device which captures and displays several digital signals at a time. Digital signals from a circuit are sampled and stored so that their states can then be displayed visually. This allows the user to analyze the timing relationships between different signals. Logic states are often displayed as wave forms or timing diagrams. Most logic analyzers can be set to trigger on a complex set of input conditions, and can decode many different communication protocols.

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A portable antenna analyzer is a device that is used to analyze the characteristics of an antenna and often the feed line. You can see some pictures of analyzers on the Wikipedia page, but generally it has at minimum a connector to attach an antenna / feed line to, a readout and dial for selecting the frequency, and a readout for the SWR of the antenna/feed line system at that frequency.

There is no need for a dummy load with an antenna analyzer, and the analyzer is designed to connect to an antenna so it generally connects the same way a transceiver would -- by connecting the feedline directly to the analyzer.

-kd7bbc

Hint: Connected, connector.

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