Waveforms from a Tektronix RSA306B with a whip antenna connected to it are examined. They are RF emissions from local FM broadcast stations.
Hi again and welcome to our 69th Test and Measurement video. In a previous video, we connected the Tektronix RSA 306B PC-based spectrum analyzer to the output from an arbitrary function generator. We saw the frequency domain representations of a sine wave, with no harmonics other than the fundamental, which is considered the first harmonic, visible above the noise floor, and of the square wave with an array of harmonics.
In today’s demonstration, we’ll connect a whip antenna to the PC-based spectrum analyzer and look at the frequency domain representation of a wide range of signals that are passing through the space around us at all times.
In a future video, we’ll connect the RSA 306B spectrum analyzer to a PCB demo board manufactured by Tektronix for the purpose of providing signals to demonstrate use of this instrument.
The RSA306B spectrum analyzer consists of electronic circuitry within an exceptionally rugged enclosure with an RF input to which the signal under investigation is connected. It also consists of the SignalVu-PC software, which is installed in the user’s PC. A standard BNC cable feeds the signal through an RF adapter into the module. There is also a USB 3.0 port, into which a USB cable is inserted. The other end connects to one of the USB slots in the PC. This cable provides both power and a two-way data connection, so that the PC, working in concert with the RSA306B module, can display a frequency domain representation of whatever signal is currently present at the module input. An elaborate interface appears on the PC screen, permitting the user to work the display so as to represent the many aspects of the signal at the module’s input.
Since the RSA306B has no external controls, moving parts or internal make and break contacts, with its rugged enclosure it should never be subject to damage. It is well suited for outdoor or factory floor usage.
Here we see the PC and module with antenna connected. Notice the array of peaks occurring between 100 and 200 MHz. These are local FM stations. The amplitude in decibels of power is shown on the Y-axis, and the frequencies of these peaks can be ascertained by counting divisions on the X-axis.
At first I was unable to display these peaks, despite repeated adjustments to the start and stop frequencies and span. The display consisted entirely of the instrument’s noise floor, and pushing Autoscale did not help. Finally, I found that the amplitude peaks appeared when I cut the resolution bandwidth, or RSB as it is known, down to one kHz.
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