RF Hardware Example: Frequency Modulation
PrintOverview
This lab is designed to examine the Frequency Modulation (FM) analog modulation scheme. Fundamentally, analog modulation techniques require changing characteristics of a carrier wave over time. These changes result in a sine wave with a different phase, amplitude, or frequency than before. In this exercise, we will construct LabVIEW VIs that transmit and receive an analog signal using Frequency Modulation.
Downloads
Filename: rfsa_demodulate_fm.vi
Requirements: View
Filename: rfsg_generate_fm.vi
Requirements: View
Background:
In the figure below, the white graph is the message signal that will be modulated. The red graph is the carrier signal with the message signal imposed upon it using Frequency Modulation. Notice that when the message signal is at its highest amplitude, the frequency of the carrier is also at its highest. When the message signal is at its lowest amplitude, the frequency of the carrier signal is at its lowest.
Programming:
Generation
1. Open a session to the NI-RFSG.
2. Configure the center frequency and output power.
3. Enable IQ Generation. This indicates to the driver to generate an arbitrary waveform (in this case an FM waveform) instead of a sine tone.
4. Generate the message signal.
5. Modulate the message signal using Frequency Modulation.
6. Write the FM waveform.
7. Initiate generation according to programmed settings.
8. Check the generation status and exit if an error has ocurred.
9. Disable the output. This sets the noise floor as low as possible.
10. Close the session to the NI-RFSG.
Acquisition
1. Initialize the RFSA.
2. Configure the RFSA Reference Clock
3. Configure the RFSA Acquisition using estimations on the carrier frequency, bandwidth and time duration of the modulated signal. Since we are interested in time domain information, we want the minimum sampling rate to be 10 times the filter bandwidth.
4. Read the captured waveform(s) from the RFSA.
5. Convert the time domain data to complex I-Q data.
6. Demodulate the FM signal acquired by the RFSA and graph the resulting waveform.
7. Extract the maximum FM Deviation from the demodulated signal.
8. If values change between acquisition, this event structure allows the Digitizer to reconfigure based on the change(s) made.
9. Close the RFSA Session.
Requirements
Filename: rfsa_demodulate_fm.vi
Software Requirements
Application Software: LabVIEW Full Development System 7.1
Hardware Requirements
Hardware Group: PXI/CompactPCI, RF
Hardware Model: PXI-5661
Driver: NI-RFSA 2.0
Software Requirements
Application Software: LabVIEW Full Development System 7.1
Hardware Requirements
Hardware Group: PXI/CompactPCI, RF
Hardware Model: PXI-5671
Driver: NI-RFSG 1.3
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