Communications Blockset

SSB AM Modulator Passband

Modulate using single-sideband amplitude modulation

Library

Analog Passband Modulation, in Modulation

Description

The SSB AM Modulator Passband block modulates using single-sideband amplitude modulation with a Hilbert transform filter. The output is a passband representation of the modulated signal. Both the input and output signals are real sample-based scalar signals.

SSB AM Modulator Passband transmits either the lower or upper sideband signal, but not both. To control which sideband it transmits, use the "upper" sideband or "lower" sideband parameter.

If the input is u(t) as a function of time t, then the output is

where:

• f_c is the Carrier frequency parameter.
• is the Initial phase parameter.
• û(t) is the Hilbert transform of the input u(t).
• The minus sign indicates the upper sideband and the plus sign indicates the lower sideband.

Hilbert Tranform Filter Parameters

This block uses a Hilbert transform filter, possibly with a compensator. These mask parameters relate to the Hilbert transform filter:

• The Time delay for Hilbert transform filter parameter specifies the delay in the filter design. You should choose a value of the form

• (N+1/2)*(Sample time parameter)

  where N is a positive integer.

• The Bandwidth of the input signal parameter is the estimated highest frequency component in the input message signal.

• This parameter is used to design a compensator for the Hilbert transform filter, which would force the message signal amplitude to remain within the assigned range. If this parameter is either 0 or larger than 1/(2*Sample time), then the block does not generate a compensator.

This block uses the hilbiir function in the Communications Toolbox to design the Hilbert transform filter.

Typically, an appropriate Carrier frequency value is much higher than the highest frequency of the input signal. To avoid having to use a high carrier frequency and consequently a high sampling rate, you can use baseband simulation (SSB AM Modulator Baseband block) instead of passband simulation.

Dialog Box

Carrier frequency (Hz)

The frequency of the carrier.

Initial phase (rad)

The phase offset, , of the modulated signal.

Bandwidth of the input signal (Hz)

The highest frequency component of the message signal. To avoid using a compensator in the Hilbert transform filter design, set this to 0.

Time delay for Hilbert transform filter (s)

The time delay in the design of the Hilbert transform filter.

Sample time

The sample time of the Hilbert transform filtering.

"upper" sideband or "lower sideband"

A string that specifies whether to transmit the upper or lower sideband. Choices are 'upper' and 'lower'.

Pair Block

SSB AM Demodulator Passband

See Also

SSB AM Modulator Baseband, DSB AM Modulator Passband, DSBSC AM Modulator Passband; hilbiir (Communications Toolbox)

References

[1]  Peebles, Peyton Z, Jr. Communication System Principles. Reading, Mass.: Addison-Wesley, 1976.

SSB AM Modulator Baseband

Tanh Nonlinearity