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FM Broadcast Modulator Baseband

Modulate using broadcast FM method

  • FM Broadcast Modulator Baseband block

Libraries:
Communications Toolbox / Modulation / Analog Baseband Modulation

Description

The FM Broadcast Modulator Baseband block creates the FM channel structure for broadcast of an FM signal. For more details, see Algorithms.

This icon shows the block with all ports enabled.FM Broadcast Modulator Baseband block showing optional input port

Examples

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Load an audio input file, and then modulate and demodulate the audio signal by using the FM Broadcast Modulator Baseband and FM Broadcast Demodulator Baseband blocks. Compare the input signal spectrum with the demodulated signal spectrum.

The doc_fmbroadcast model loads the guitar.wav signal, modulates the signal for FM broadcast, demodulates the FM broadcast signal, and then compares the recovered signal to the original audio signal in a spectrum analyzer.

Limitations

  • If you select RDS/RBDS modulation, both the audio and RBDS inputs must satisfy this equation:

    audioLengthaudioSampleRate=RBDSLengthRBDSSampleRate

  • The input length of the audio signal must be an integer multiple of the audio decimation factor.

  • The input length of the RBDS signal must be an integer multiple of the RBDS decimation factor.

Ports

Input

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Audio signal, specified as one of these options.

  • N-element column vector for mono signals — If you do not select Stereo audio, you must specify the audio signal as a column vector. N is the number of samples in the audio signal.

  • 2-by-N matrix for stereo signals — If you select Stereo audio, the audio signal must have two channels and the block performs stereo encoding after pre-emphasis filtering. N is the number of samples in the audio signal per channel.

For information about signal length restrictions, see Limitations.

Data Types: double | single
Complex Number Support: Yes

RDS (or RBDS) signal, specified as one of these options.

  • N-element column vector for mono signals — If you do not select Stereo audio, you must specify the audio signal as a column vector. N is the number of samples in the audio signal.

  • 2-by-N matrix for stereo signals — If you select Stereo audio, the audio signal must have two channels and the block performs stereo encoding after pre-emphasis filtering. N is the number of samples in the audio signal per channel.

For information about signal length restrictions, see Limitations.

Data Types: double | single
Complex Number Support: Yes

Output

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FM-modulated baseband signal, returned as a column vector of complex values of the same data type as the input signal. The length of this output is length(Input 1 × Sample rate (Hz) / Sample rate of audio input signal (Hz)).

Parameters

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To edit block parameters interactively, use the Property Inspector. From the Simulink® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Output signal sample rate in Hz, specified as a positive scalar. The sample rate must be greater than twice the frequency deviation. Specifically, Sample rate > 2×Frequency Deviation.

Peak deviation of the modulator output signal frequency in Hz, specified as a positive scalar. The frequency deviation must be less than half the sample rate.

The system bandwidth equals two times the sum of the frequency deviation and the message bandwidth. FM broadcast standards specify a value of 75 kHz in the United States and 50 kHz in Europe.

Pre-emphasis highpass filter time constant in seconds, specified as a positive scalar. FM broadcast standards specify a value of 75 μs in the United States and 50 μs in Europe.

Sample rate of the input audio signal in Hz, specified as a positive scalar.

Select this check box if the input signal is a stereophonic audio signal. If you do not select, the audio signal is assumed to be monophonic. If you select the Stereo audio check box, the block modulates the stereo audio (LR) at the 38 kHz band, in addition to the baseband (L+R). For more information, see Multiplexed Stereo and RDS (or RBDS) FM Signal.

Select this check box to modulate a baseband RBDS signal at 57 kHz. For more information, see Multiplexed Stereo and RDS (or RBDS) FM Signal.

Oversampling factor of the RDS (or RBDS) input signal, specified as a positive integer. The sample rate of RDS (or RBDS) broadcast data is 1187.5 Hz. The RDS (or RBDS) signal sample rate is (Oversampling factor of RDS/RBDS input × 1187.5) Hz.

Dependencies

To enable this parameter, select RDS/RBDS modulation.

Type of simulation to run, specified as Code generation or Interpreted execution.

  • Code generation — Simulate the model by using generated C code. The first time you run a simulation, Simulink generates C code for the block. The model reuses the C code for subsequent simulations unless the model changes. This option requires additional startup time, but the speed of the subsequent simulations is faster than with the Interpreted execution option.

  • Interpreted execution — Simulate the model by using the MATLAB® interpreter. This option shortens startup time, but the speed of subsequent simulations is slower than with the Code generation option. In this mode, you can debug the source code of the block.

For more information, see Simulation Modes (Simulink).

Block Characteristics

Data Types

double | single

Multidimensional Signals

no

Variable-Size Signals

no

Algorithms

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The FM Broadcast Modulator Baseband block includes the functionality of the FM Modulator Baseband block, plus de-emphasis filtering and the ability to receive stereophonic signals.

References

[1] Hatai, I., and I. Chakrabarti. “A New High-Performance Digital FM Modulator and Demodulator for Software-Defined Radio and Its FPGA Implementation.” International Journal of Reconfigurable Computing (December 25, 2011): 1–10. https://doi.org/10.1155/2011/342532.

[2] Taub, H., and D. Schilling. Principles of Communication Systems. McGraw-Hill Series in Electrical Engineering. New York: McGraw-Hill, 1971, pp. 142–155.

[3] Der, Lawrence. "Frequency Modulation (FM) Tutorial." Silicon Laboratories Inc., pp. 4–8.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2015a