A Tektronix RSA306B PC-based spectrum analyzer is connected to the output from a Tektronix RTSA V3 Demo Board in order to demonstrate power measurements in the frequency domain.
Hi and welcome to our 71st Test and Measurement Video. Today we’ll continue our demonstration of the Tektronix RSA306B PC-based spectrum analyzer connected to the Tektronix RTSA V3 Demo Board. Previously, using this connection, we viewed a CW signal, displayed in the frequency domain. Now, we’ll look at power measurements with markers.
It is feasible to measure the power of a modulated signal without setting up a channel power measurement. We can use SignalVu-PC to perform integrated power and power density measurements by means of power markers.
When measuring signal density, the signal will be seen to resemble noise. Measurements are performed at 1 Hz bandwidth. Accurate results can be achieved because the selection of power measurement markers automatically switches the trace detector to average RMS.
To do these measurements, the RSA306B spectrum analyzer, the PC with SignalVu-PC software installed and the RTSA V3 Demo Board are connected in the usual way. The dual end of the Y-type USB cable is connected to two USB slots in the PC and the single end is connected to the Demo Board. The purpose of this unusual hookup is to provide ample current for the Demo Board without stressing the PC.
Then, another USB cable is run from the PC to the RSA306B module. This cable carries data in both directions. Finally, a BNC cable is run from an RF adapter at the module to the appropriate Demo Board output. That completes the cabling. What remains is to configure SignalVu-PC software by means of PC controls.
The basic Demo Board settings are the same as in our previous demonstration for the CW signal in Test and Measurement Video 70:
1. Press the On button in the Demo Board. LED’s throughout light up indicating that the Demo Board is prepared to output signals to the connected RSA306B spectrum analyzer and through it to the PC.
2. Set the reference to Internal.
3. Set the Run Mode to Free Run.
4. Click the Row and Column buttons to select CW to determine the Demo Board output. This completes the procedure for configuring the Demo Board. Now we will turn to the RSA306B.
5. Double click the SignalVu-PC icon on the desktop.
6. Click Connect to Instrument.
7. Click OK in the Connect Status Box.
8. Click on the gear graphic to display the Settings Control Panel.
9. Click Max Span to extend the spectrum range to its maximum possible extent. Start and Stop frequencies will align themselves.
10. Set Resolution Bandwidth to 1.0 kHz. This determines the Fast Fourier Transform bin size, which is the smallest frequency that can be resolved. This improves selectivity at the expense of sweep speed and update rate.
The only difference is that we use the Row and Column buttons to change the signal type from CW, which stands for continuous wave, to OFDM, which stands for orthogonal frequency division multiplexing. This is a very popular method that is used to encode digital data on multiple carrier frequencies. We see it in wideband digital communication including such diverse applications as digital television, audio broadcasting, DSL Internet access, wireless networks, power line networks and 4G mobile communications. Many closely-spaced orthogonal subcarriers coexist as parallel data streams or channels.
With the Demo Board settings completed as in the previous video:
1. Now click the Stop button to pause the measurement.
2. Then drag the marker reference, denoted by MR on the left side, and marker 1, denoted by M 1 on the right side of the OFDM spectrum.
3. Click the Define button in the Marker settings.
4. Within the Marker Properties tab, in the Readouts dropdown box, select Power.
Phase noise can be measured by setting the delta marker to dBc/Hz. Advanced power measurement and ACLR (Adjacent Channel Leakage Power Rate) can be done in Channel Power and ACPR display.
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