A new Tektronix PC-based spectrum analyzer is described and configured to a Windows laptop computer, and its use is demonstrated.
Hi and welcome to our 68th Test and Measurement video. Today we’ll do an overview of the Tektronix amazing breakthrough RSA306B PC-based spectrum analyzer.
To generalize, the spectrum analyzer is similar to the oscilloscope, but with three major differences:
• It displays oscillating signals in frequency domain as opposed to the oscilloscope’s time domain with additional frequency domain capability.
• The spectrum analyzer has greater potential frequency response although the span, which is adjustable, is at a given point in time typically narrower.
• The spectrum analyzer, unless it is PC-based, is more expensive than an oscilloscope of comparable specifications.
Now that Tektronix has come out with the RSA306B PC-based spectrum analyzer, the high-cost barrier has been breached and you can have an advanced instrument without mortgaging your real estate to purchase an equivalent bench-type spectrum analyzer. The rationale for this is that everyone owns or can easily acquire a PC. (The laptop is convenient if you intend to do outdoor or factory floor work. AC is not required because the RSA306B is powered through a simple USB hookup to the laptop, and this cable also carries data in both directions.)
The Tektronix unit has no front or back panel controls, internal contacts or moving parts. Everything is controlled by the PC, so it is hard to imagine that the spectrum analyzer, with its exceptionally ruggedized enclosure, would ever be damaged unless excessive voltage is applied at the RF input.
The amazing and complex functionality of this black box is in the extensive software, SignalVu-PC, which comes in a flash drive supplied with the RSA306B. It is also available as a free download at the Tektronix website.
After SignalVu-PC has been downloaded, it needs to be installed. To do this, use Windows Explorer to navigate to the folder that was extracted from the archive. Then, double-click Setup.exe. Follow the on-screen instructions to install the software.
The next step is setting up the live link. Cabling is very simple. We are using a Tektronix MDO 3000 series oscilloscope with internal AFG to supply a signal for the purpose of this demonstration. First, with the AFG output connected to analog Channel One input in the oscilloscope, obtain a sine wave and display it on the screen.
Then, in Waveform Settings, use Multipurpose Knob a or the numerical pad to set the frequency of this sine wave to the highest possible, which is 50 MHz.
Now, swing the BNC cable over to the PC-based spectrum analyzer, using an RF adapter. Additionally, this unit is connected to the PC through a USB cable, which provides both power and data interface.
Double-click the SignalVu-PC icon on the computer desktop, and the program will open.
Click Live Link on the menu bar to view the drop-down menu. Click Search For Instrument. A message appears stating that the instrument was found. Click Connect To Instrument. In the future, this configuration will be automatic, so all you have to do is open SignalVu-PC.
Here, in the spectrum view, is the sine wave. Since the frequency in the AFG output is 50 MHz, we have to set up the spectrum analyzer so that the signal can be displayed. To move the fundamental to the center of the screen, Start frequency, Stop frequency and Span have to be set correctly. The procedure is to subtract and add equal amounts to the signal and type these figures into the Start and Stop fields. The instrument will compute the span.
Notice that there are no visible harmonics. In a sine wave all the power is at the fundamental.
Now we have set the AFG output to Square Wave. Here again the frequency is 50 MHz. Stop, Start and Span are the same as for the sine wave. The only difference is that a strong harmonic is shown with about 10 dB less amplitude than the fundamental. That is the nature of the square wave. The fast rise and fall times generate strong harmonics and these sine waves add to one another to form a complex signal in accordance with Fourier theory.
If we change the Span to 100.0 MHz, Start and Stop frequencies are computed. Now we see more harmonics with successively lower amplitudes.
Because these values are shown in decibels rather than volts, the amplitude drop-off is far steeper than it appears in the frequency domain graph.
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