This example uses the USRP as a spectrum analyzer to both find local FM radio stations and listen to their live broadcast(s).
Check out this Teaching Tough Concepts--Understanding RF Radio Broadcast white paper to learn more about Broadcast Radio and Frequency Modulation.
1. Open the document: Find Radio Station.gvi
2. Verify the correct IP Address of your USRP is set under device names (typically 192.168.10.2)
3. Configure the remaining Front Panel parameters as follows:
|Device names||192.168.10.2 (typically)|
|Number of Samples||20k|
NOTE: Capitalization is important when entering parameters like IQ Rate and Carrier Frequency. Capital M is interpreted by LabVIEW as "Mega-" while lower case m is interpreted as "-milli."
4. Run the VI (Note: if it errors try and decreasing the number of samples to 10,000)
5. Note the various peaks that should be visible in the resulting Frequency Plot -- this will vary depending on the physical 6. location where this example is performed and what FM stations are available. Remember that 0 on the graph represents 7. the carrier frequency specified in step 3. An example plot os provided in Figure 1.
8. If you zoom in to a particular area (peak) of interest, you may also notice that the bandwidth of the radio station is +/- 100kHz (a total of 200kHz).
NOTE: a simple way to explore the data in LabVIEW Communications is to right click on the indication (in this example, Frequency Plot) and select Capture Data. You can then double-click the captured data item in the Data pane on the left of the workspace to open the data view. In this view, you can effortlessly browse the captured data set, zooming in to areas of interest and in this case identifying a particular radio station's center frequency and bandwidth.
1. Once you have observed the spectrum and selected a particular station's center frequency, you can adjust the parameters of the Find Radio Stations VI to observe that station more closely.
2. Adjust the Carrier Frequency and Bandwidth inputs to whatever you determined in the last section (we'll be using 93.7 MHz and 200 kHz, respectively)
3. Run the VI once again, and observe the resulting Frequency Plot, similar to the one in Figure 2.
Now that a station has been identified, we will tune to that station and create an audio output of the live broadcast through our computer's speakers.
Press Ctrl+E to switch to the Front Panel of the VI.
Run the VI and listen to output.
You’ve now demodulated broadcast FM radio using the mathematical approach
Additional Images or Video
LabVIEW 2014 version of this example is available here.
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