By Varun Merchant
The Worldwide Spectrum Allocations poster arrived in the mail last week – it offers a beautiful visual of the FCC allocated spectral bands all in one place – and is now pinned to the cube wall that overlooks my MDO4000B mixed domain oscilloscope.
Here’s a thumbnail of the poster. Click here to order one for your cube or office wall.
The location is strategic since the MDO4000B oscilloscope has a built-in 6 GHz spectrum analyzer with RF triggering. Just as the spectrum allocation chart has all the bands displayed in one place, the MDO4000B allows you to visualize analog, digital, and RF signals on the same screen, all at once – and what’s more, all these signals can be triggered in the time or frequency domain. Take a look at an illustration below:
Fig 1- The MDO4104B mixed domain oscilloscope displaying analog, digital and RF signals
The MDO4000B does not simply use an FFT to represent the spectrum. It has dedicated RF acquisition hardware that when coupled with the oscilloscope’s acquisition system offers exceptionally wide capture bandwidth. This wide capture bandwidth, combined with the 125 different triggering combinations, comes in handy when trying to isolate and find the root-cause of RF system level issues.
Time alignment of signals in the time and frequency domain is also important when it comes to understanding turn-on characteristics of power amplifiers, for example. Spectral purity of the power amplifiers can be assessed before, during and after turn-on simply by scrolling through the time domain waveform using a feature known as “spectrum time” (the orange bar in Fig.1). A slower rise time in the PA’s control signal will adversely affect its spectrum while it is in a transient mode.
On the other hand, if you are using WLAN modules in your system, the MDO4000B paired with SignalVu-PC software allows for vector signal analysis of WLAN signals. Depending on what modulation coding scheme your module follows, you can set up the tool to view constellation diagrams and evaluate metrics such as EVM (error vector magnitude). To take it a step further, you can also plot EVM vs. symbol and EVM vs. sub-carrier to learn how the quality of modulation changes with time.
As you might have guessed, this is only a drop in the ocean of applications that the MDO4000B spectrum analyzer and scope can be used to address. If you’re curious about how Tektronix incorporates so much versatility into one instrument, take a look at The Secrets Behind the MDO4000B Spectrum Analyzer white paper or browse through some informative videos on the MDO4000B’s RF capabilities. Then be sure to order up a free copy of the Worldwide Spectrum Allocations Poster to decorate your cube or home office and provide a useful reference at the same time.
Since publishing the above blog, Tektronix is currently offering a free upgrade to 3/6 GHz spectrum analyzers and a free bundle of software applications on mixed-domain oscilloscopes.