VIDEO: Detecting and Measuring Short Distance Dynamic Signals in the Tektronix RSA306 Spectrum Analyzer

A PC-based spectrum analyzer built by Tektronix is used to receive and analyze short-distance dynamic 2.4 GHz signals that may create interference in the industrial, scientific and medical bands.

Greetings and welcome to our 80th Test and Measurement Video. Again we’re focusing on the Tektronix RSA306 PC-Based Spectrum Analyzer. This instrument is an economical alternative to the bench-type spectrum analyzer, which typically costs several thousand dollars more than an oscilloscope having parallel specifications. The reason for the reduced price is that the RSA306 is a simple module that plugs into a user-supplied PC and takes advantage of the enormous computing power and beautiful display capability therein. Tektronix furnishes free of charge the relevant software, SignalVu-PC, which can be downloaded from the website or from a flash drive furnished with the module. The RSA306 has no external controls, internal power supply, moving parts or electrical contacts, and with a ruggedized enclosure it is suitable for the factory floor or use outside. Almost everyone on the planet owns or has access to a late-model PC, so that part of the price can be discounted.

Today’s demonstration involves detecting and measuring short-distance dynamic RF signals such as bursted packet transmissions originating from a wireless local area network or Bluetooth source. Interference from these ubiquitous transmissions can be problematic because they share spectral territory with the 2.4 GHz industrial/scientific/medical band. We’ll focus on this difficulty, using the RSA306 PC-Based Spectrum Analyzer connected to a laptop PC and whip antenna. Unlike some of our previous demonstrations, we won’t be using the Demo Board that Tektronix supplies to demonstrate the RSA306 spectrum analyzer. Instead, we’ll be sourcing the signals using devices found in most homes.

Having cabled the RSA306 Spectrum Analyzer to a laptop PC, we’ll attach the whip antenna to the RF input on .the module. That completes the hardware configuration. Now we have to set up the RSA306 using the PC interface. First, in the PC, open SignalVu-PC by clicking on the desktop icon.

Then, in the software interface on the PC, click the Preset button and the Display button.

In General Signal Viewing under Measurements, select DPX from. the Available displays box. Click the Add button This will add the DPX icon to the Selected displays box (and remove it from the Available displays box). Click the OK button.

In the DPX display, set the center frequency to 2.46200 GHz or to one of the WLAN channels. Set the span to 40.00 MHz.

There are 14 channels designated in the 2.4 GHz range (2400-2483.5 MHz). They are spaced 5 MHz apart. The most common are channels 1 (2412 MHz), 6 (2437 MHz) and 11 (2462 MHz). Most routers use one of them as the default channel.

Select the Split view.

Set the Reference Level to -4 dBm.

In the DPX display, click the settings button (gear icon).

Under the Bitmap Scale tab, set the Max scale to 3 percent for the DPX Spectrum display.

Under the Amplitude Scale tab, set the max color scale to -40 dBm for the DPXogram Display.

In the Traces tab, set the Dot Persistence to Infinite.

In your smartphone, tablet or PC, turn the WLAN function Off, then On while monitoring the setup above.
Check the DPX display to see if you can see the spectrum of the WLAN signals. If no signals, change the Center Frequency of the RSA306 to other channels.

You can set the Dot Persistence to be variable or infinite.

In variable persistence mode, you can specify a decay period that limits how long the point will be displayed.

In infinite persistence mode, once a point in the display has been written to, it will remain visible indefinitely.

We start with infinite persistence because it ensures that all transients will be kept on screen.

To better observe the WLAN activities in the DPX display, you can cause both uplink and downlink activity on your device by navigating to an Internet Speed Testing webpage to test both the uploading and downloading speed, and monitor the DPX display of the RSA306 at the same time.

Turn the Bluetooth function Off, then On in your smartphone, tablet or PC while monitoring with the setup above.

Click Stop to stop the acquisitions when you have a pattern on the spectrogram you would like to examine.
Right click the display, and click Add Markers twice to add two markers. Then you can measure the distance between hops in frequency and time using the markers on the spectrogram.

This is the real-time display in the RSA306. You can see a typical WLAN interchange between a nearby smart phone and a more distant network access point. The smartphone signal is nearly 30 dB stronger than the access point’s signal because it is closer to the spectrum analyzer’s antenna. You can also see the Bluetooth signals and even the measurements of the time and frequency intervals between those hop signals.

Thanks for watching. New videos are added periodically, so check back frequently.