PC-based oscilloscopes have been around for quite some time. Now Tektronix has added to the mix by bringing out a PC-based spectrum analyzer with essentially the same features found in advanced bench-type models but at a fraction of the price.
The rationale behind this innovation is that a substantial cost reduction is possible given the fact that most users already have access to a PC. As for the RSA306B module itself, it has no front or back panel controls or moving parts, so together with an exceptionally ruggedized enclosure, the unit can be expected to last indefinitely unless it is exposed to overvoltage at the input or lightning-induced transients.
The SignalVu-PC software comes with the RSA306B in a flash drive, or it can be downloaded free of charge from the Tektronix website even if you haven’t made the purchase. When the download is complete, double-click the SignalVu-PC icon on the computer program. Click Live Link on the menu bar to view a drop-down menu. Click Search for Instrument. A message will appear stating that the instrument has been found. Click Connect to Instrument. In the future, it is only necessary to open SignalVu-PC because the configuration is automatic.
Hooking up and getting started are simple. A USB cable connects the spectrum analyzer to the PC. As often the case in USB setups, one-way power and two-way data are simultaneously conveyed to the detriment of neither.
Then, a BNC cable from the signal source is connected to the RSA306B RF input, using an RF adapter. To see the RSA306B spectrum analyzer in action, it is necessary to connect a signal to the input. Unlike oscilloscopes, spectrum analyzers are not normally supplied with probes. Instead, there is the BNC cable.
Three signal sources suggest themselves. The first and most obvious is the arbitrary function generator, successor to the old-time signal generator. Our contemporary high-end oscilloscopes contain optional arbitrary function generators with output ports suitable for BNC connection. The BNC cable can be connected to one of the analog channel inputs. Pushing AFG, the signal appears in the display. Then, pressing the soft key associated with waveform, an on-screen menu appears that permits the user to scroll through the library of internally synthesized waveforms – sine wave, square wave, pulse, noise etc.
The soft key associated with waveform settings permits the user to select frequency, period, amplitude, offset, high level and low level for whatever was previously chosen.
Swinging the output end of the BNC cable over to the RSA306B, the waveform is conveyed through the spectrum analyzer to the PC where it appears in the display. This is a bit counter-intuitive at first because operations performed on the oscilloscope do not show up in the oscilloscope since the AFG output is no longer fed back into it.
Two other signal sources are the Tektronix demo board designed to go with the instrument we are considering, and secondly the supplied whip antenna, which fastens to the RF input through the RF adapter.
The demo board is powered by a Y-type USB cable, with the double end connected to two USB slots in the computer. This cable, as usual, carries both power and data. The reason for the double end is that the demo board, when working hard, draws an amount of current that could overload the computer if a single USB port had to carry the entire load. The setup might function properly, but extended use could make heat in the wrong place.
The BNC cable connects to any of the demo board outputs. The ROW and Column switches at the bottom left corner function as you would expect, with LEDs indicating the type of output.
Another signal source is the whip antenna, which is supplied along with the RSA306B PC-based spectrum analyzer. It threads directly into the module’s RF input with no additional adapter needed.
The spectrum analyzer-antenna combination has been used for a long time with outstanding success. This equipment can monitor RF bands to determine compliance and to look at assigned frequencies to check for interfering signals. Another application is in medical facilities to determine if out-of-band interference could pose a threat to the proper operation of life-support and diagnostic equipment.
The spectrum analyzer is capable of providing far more information than a simple RF detector because it shows the amount of power at the antenna at various frequencies. If used to detect clandestine surveillance equipment, say, the analyzer should be capable of having the frequency span set to a broad range. In a swept spectrum unit, a fast tuning speed is needed. Together with good sensitivity and selectivity, remote or computer control is desirable, and in this regard the PC-based spectrum analyzer is a logical choice.
The Tektronix RSA306B PC-based spectrum analyzer is a real-time as opposed to a swept-spectrum instrument. The older swept-spectrum technology is less expensive, and for this reason, it has not been entirely supplanted by real-time instrumentation.
For perspective, it is worthwhile to consider the most basic type of frequency domain analysis, Fast Fourier Transform (FFT), which is built on a set of algorithms derived from Fourier analysis. The problem with traditional analysis/synthesis is that the mathematics is enormously complex. In the 1960s, researchers formulated FFT, enabled by matrix theory, greatly simplifying time and frequency domain transitions. Invoking the Math menu, an oscilloscope user can instantly see a signal (previously only viewable in the time domain) in the frequency domain, merely by pressing the soft key associated with FFT.
All of this preceded the swept spectrum and later the real-time spectrum analyzer. In the swept spectrum instrument, superheterodyne technology as used since the 1920’s in radio reception and today in TVs as well, is employed to process the signal and prepare it for display in the frequency domain.
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