A square wave displayed through a probe shows rounded corners. The remedy is to
Answer: C
Rounded corners mean the probe passes the high frequencies less readily than the low, that is under compensation. The trimmer is adjusted while watching the calibrator square wave until the top of the wave is flat and the corners square.
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A single trace is wanted of a switching transient that occurs once. The instrument to use is
Answer: D
A sampling oscilloscope needs the waveform to repeat, since it builds the picture from many cycles, and a free-running base would almost certainly be elsewhere when the event happened. Only a storage instrument triggered by the event itself will capture it.
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The graticule of an oscilloscope is marked on the inside surface of the screen in better instruments so as to avoid
Answer: A
An external graticule sits a few millimetres in front of the phosphor, so the reading changes as the observer's eye moves. Marking it on the inner face puts scale and trace in the same plane and removes the error entirely.
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The calibrator output provided on the front panel of an oscilloscope is used to check
Answer: B
It is a square wave of accurately known amplitude and, usually, a round frequency. Displaying it confirms the volts per division calibration and, since it has fast edges, provides the waveform against which a probe trimmer is set.
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Comparing the analogue and digital storage oscilloscope for viewing a signal with rare glitches, the analogue instrument
Answer: C
The analogue instrument writes every sweep to the phosphor, so an infrequent event appears as a faint trace against the bright envelope, and the relative brightness itself conveys how often it happens. A digital instrument may miss it entirely between acquisitions unless a peak detect mode is used.
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The Z axis input of an oscilloscope allows an external signal to control
Answer: D
It is connected to the control grid circuit, so an external waveform can brighten or blank the beam. Marking a trace with timing pips from a standard frequency source is the classic use, and it also serves for intensity modulation in raster displays.
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An oscilloscope is used to display the characteristic of a diode by applying the diode current to the vertical channel and the diode voltage to the horizontal. This requires
Answer: A
Plotting one quantity against another is exactly what X-Y mode provides, the horizontal plates being driven by the second signal instead of by the sawtooth. A current sensing resistor converts the current into the voltage the vertical channel needs.
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The reason a general purpose oscilloscope uses electrostatic rather than electromagnetic deflection is that electrostatic deflection
Answer: B
Deflection coils are inductive and their impedance rises with frequency, so driving them at megahertz rates is impractical. Plates present a small capacitance and can be driven to hundreds of megahertz, which is what an oscilloscope needs above all else.
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The horizontal magnifier control of an oscilloscope, marked times ten, works by
Answer: C
The sweep itself is unchanged but the horizontal amplifier gain is raised tenfold, so a tenth of the sweep fills the screen. Any part of it can then be examined by shifting with the horizontal position control, at the cost of a dimmer and less accurate trace.
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A wide band oscilloscope is terminated in 50 \( \Omega \) at its input rather than presenting one megohm because
Answer: D
At high frequencies an unterminated cable reflects, and the reflections appear on the screen as ringing that has nothing to do with the signal. Matching the cable in its characteristic impedance absorbs the wave, at the cost of loading the source with fifty ohms.
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