The Tektronix MDO 3104 oscilloscope is called by the manufacturer a six-in-one instrument. Besides being a basic bench-type digital storage oscilloscope, it incorporates five other digital-based tools: spectrum analyzer, logic analyzer, function generator, digital voltmeter, and a protocol analyzer for serial data buses.
The spectrum analyzer is traditionally a stand-alone instrument. It lets the user view signals in the frequency domain. The Y-axis represents amplitude as in a conventional oscilloscope, a significant difference being that rather than displaying voltage on a linear scale, amplitude is depicted as power on a logarithmic scale in the form of decibels.
But what is really special is that the horizontal Y-axis represents frequency rather than time. Accordingly, the display exhibits an entirely different view of the signal. It has a strikingly different appearance and provides unique insights. Despite this fact, both displays are derived from the same information, and no data is gained or lost translating back and forth. The two displays are complex and mathematically difficult Fourier Transforms of one another, performed at the click of a button on the oscilloscope.
A valuable enhancement that is an adjunct to the spectrum analyzer is the integrated spectrogram. It provides still another view of the signal, now with a different axis configuration. As in the spectrum analyzer display, in the spectrogram the X-axis represents frequency. However, the Y-axis represents time rather than amplitude, and of course this makes for a totally different appearance of the graphic. Additionally, there is a third variable, amplitude.
Because it’s not possible to display three axes in a two-dimensional screen, various amplitudes are depicted by different colors. Cold colors, blue and green, indicate low amplitude, while yellow and red, the hotter colors, represent higher amplitude. As the oscilloscope creates new acquisitions, they are inserted at the bottom of the display, and the representation moves up on the screen accordingly.
To bring up the spectrogram, press spectrogram in the RF menu. A vertical menu now appears to the right of the display. Use the appropriate soft key to turn the spectrogram display on.
What is really valuable in the spectrogram feature is the ability to review signal history. First stop the acquisitions. At this point, the spectrogram view reverts to the generic spectrogram trace. It is now possible to view the acquisition history by pressing the side menu slice control and turning the ubiquitous Multipurpose Knob a.
This information is valuable in revealing glitches and anomalies due to design or construction faults in a new product, particularly with reference to the use of markers and other analytic tools.
Filed Under: Test & Measurement Tips