Instrument Function > Modulation > Overview of Modulation
Overview of Modulation

Analog modulation is a method used to transmit information of an LF (Low Frequency) signal in accordance with a second signal, typically one of a higher frequency. This is done by varying one or more properties of a high frequency waveform, called the modulation or carrier signal, with the modulating signal that contains the information to be transmitted.

The three key parameters of the modulation signal are the amplitude, phase and frequency. These parameters are modified in accordance with the low frequency signal to obtain the modulated RF signal.

The R&S SMA provides all the various types of modulation, such as:
  • AM (Amplitude Modulation)
  • FM (Frequency Modulation, analog and digital)
  • PhiM (Phase Modulation, analog and digital)
  • PULM (Pulse Modulation)
  • Chip Modulation
The RF signal can be modulated with a wide variety of internally generated modulations waveforms, for example sine waves, triangle/rectangular/trapeze signals, and noise. The basic unit basic unit (R&S SMA + frequency option R&S SMA-B10x) provides analog amplitude and pulse modulation without additional equipment options. A standard LF generator and a pulse generator are provided for generating the internal modulation signal. Further available options are:
  • R&S SMA-B20 (FM/PhiM Modulator) for performing Frequency modulation (FM) and phase modulation (PhiM)
    R&S SMA-B22 (Enhanced Phase Noise Performance andFM/PhiM Modulator)
    Chirp modulation is available with one of these options and an interface board with part number 1400.0530.02.
  • R&S SMA-K23 High Performance Pulse Generator features extended pulse modulation
  • R&S SMA-K24 Multifunction Generator provides a second LF Generator and a Noise generator
    The LF Generator can be used as a second modulation source with extended frequency range and selectable signal shapes. The noise source provides white noise with selectable bandwidth and level distribution as additional modulation source.
  • R&S SMA-K25 VOR/ILS Modulation for generating test signals for avionic systems (VOR (VHF Omnidirectional Range), ILS-GS (Instrument Landing System - Glide Slope), ILS-LOC (Instrument Landing System - Localizer) and Marker Beacon).
  • R&S SMA-K26 DME Modulation
  • R&S SMA-K27 Pulse Train enables generation of pulse trains

Settings for the modulation are made in separate modulation menus. These menus can be accessed in the block diagram by way of the "Modulation" function block, or by means of the menu with the same name which is opened using the MENU key.

 


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