FM Modulator Passband

Modulate using frequency modulation

• 

Libraries:
Communications Toolbox / Modulation / Analog Baseband Modulation

Description

The FM Modulator Passband block modulates a signal using frequency modulation. The output is a passband representation of the modulated signal. The frequency of the output signal varies with the amplitude of the input signal. Both the input and output signals are real scalar signals.

Examples

Modulate and Demodulate FM Passband Signal in Simulink

Sample a 100 Hz linear frequency sweep chirp with a 400 Hz target frequency at 4 kilosamples per second. Modulate the input signal using the frequency modulation method. Demodulate the signal. Plot the input signal, the modulated signal, and the demodulated signal.

The fmmoddemod_passband model modulates the input linear frequency sweep chirp signal using the FM method at a carrier frequency of 1.5 kHz with 50 Hz frequency deviation and then demodulates the signal. When the model runs, it plots the signals. This configuration ensures the Hilbert transform filter operates in the flat section of the magnitude response and that the demodulated signal has the desired magnitude and form.

The spectrum analyzer plot shows input signal, the modulated signal, and the demodulated signal.

Limitations

• This block does not work inside a triggered subsystem.

Ports

Input

In — Input signal

scalar

Input signal, specified as a scalar.

This port is unnamed on the block.

Data Types: double

Output

Out — Output signal

scalar

Output signal, returned as a scalar. The output is a passband representation of the modulated signal.

This port is unnamed on the block.

Data Types: double

Parameters

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

Carrier frequency (Hz) — Carrier frequency in Hz

300 (default) | positive scalar

Carrier frequency in Hz, specified as a positive scalar. Match the carrier frequency, f_c, to the corresponding FM Demodulator Passband block.

Typically, an appropriate carrier frequency is a much higher than the highest frequency of the input signal. By the Nyquist sampling theorem, 1 / T_s > (2 × f_c), where T_s represents the sample time of the input signal. For more information, see Baseband vs. Passband Simulation.

Initial phase (rad) — Initial phase offset in radians

0 (default) | scalar

Initial phase offset of the carrier in radians, specified as a scalar.

Frequency deviation (Hz) — Frequency deviation of carrier frequency in Hz

50 (default) | scalar

Frequency deviation of the carrier frequency in Hz, specified as a scalar. Also known as the variation in the frequency.

Block Characteristics

Data Types	double | single
Multidimensional Signals	no
Variable-Size Signals	no

Algorithms

The FM Modulator Passband block uses frequency modulation to encode information in a carrier wave by varying the instantaneous frequency of the signal. For an input signal u(t), as a function of time t, the output signal is

$$\cos \left(2\pi f_{c}t+2\pi K_c{\displaystyle {\int }_0^{t}u(\tau )d\tau +\theta }\right)$$

where:

• f_c represents the Carrier frequency (Hz) parameter.

• θ represents the Initial phase (rad) parameter.

• K_c represents the Frequency deviation (Hz) parameter.

Extended Capabilities

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

Version History

Introduced before R2006a