You Are Here:
You are here: Features & Functionality > "Options" Menu > Signal Generator

Signal Generator

Every GSG model can be operated as a signal generator, i.e. to generate one, or—if so equipped—several satellite signals (with no Doppler), or one carrier frequency.

In Signal Generator mode, advanced GSG units can support: GPS, GLONASS, Galileo, BeiDou, SBAS. If equipped with the L2 and/or L5 options, GSG allows the selected satellite(s) to transmit all signals enabled on that satellite.

Note: For more information on available GSG models and options, see GSG Series Model Variants and Options.

To configure the Signal Generator mode, navigate to Options > Signal Generator:

Signal Generator configuration view (depends on licensing options installed)

The following Signal Generator options can be configured:

Signal type

The Signal type selection will open a new view, as shown below. Note that the view depends on the licensing options installed on your unit.

Signal types configuration view

 

In Signal Generator mode, GSG offers the following Signal type configuration options:

  • GNSS systems currently supported are: GPS, Glonass, Galileo, BeiDou, and QZSS, and their corresponding signal types. For information on signal types, see also Frequency Bands and Signal De-/Activation.
  • Pseudo-encryption (P(Y)): For more information, see Encryption.
  • SBAS Signals: It is possible to generate a signal for any of the SBAS PRNs. However, GSG can generate a real SBAS message stream only if the chosen PRN corresponds to a live SBAS satellite (see SBAS Satellites for further details).

    Note: The SBAS signal type is only available with GSG-55, GSG-56, and GSG-6 Series units.

    Note that in signal generator mode (unlike in constellation simulation mode), GSG will always attempt to download SBAS data. If such data is not available, then MT63 (i.e., “null messages”) will be transmitted.

  • Modulation options:
    • Modulated: This is the default mode, transmitting standard, modulated signals.

    • Sweep or Noise: In addition to the modulated signals, sweeping interference or narrowband noise interference will be transmitted. Currently it is not possible to use sweep/noise with unmodulated signals.
    • Pure Carrier Signal: GSG will transmit an un-modulated signal (pure carrier), using the user-specified signal strength, and frequency offset from the nominal frequency. With GSG-6 series simulators, it is possible to generate carrier signals for L1 and L2 at the same time.
    • Prn: Pseudo-random noise

Satellite ID

The Satellite ID field is used to specify the GPS PRN, Galileo PRN, and the GLONASS satellite ID, therefore it is limited to 24 (the highest GLONASS satellite ID). If this field is set to a value higher than 24, then GLONASS will not be selectable under Configure signal types.

Transmit power

The term Transmit Power refers to the power transmitted by GSG during the execution of the currently chosen scenario.

  • The transmit power is specified in dBm.
  • The supported range is: Max. -65 dBm … Min. -160 dBm.

    Note: External Attenuation setting decreases the Max value. For more information, see Transmit PowerExternal Attenuation.

    Note: When the power settings of individual channels change during scenario execution (via the > Events menu, or SCPI commands) the power range will be further limited so that the maximum difference between the strongest and the weakest signal is never more than 72 dB.

  • The resolution is: 0.1 dBm.
  • Default setting: -125.0 dBm

Caution: If you are using an antenna (rather than an RF cable), see Signal Power Level Considerations regarding signal level compliance in the U.S. If you live in other countries, check your local emission standards.

Frequency offset

The Frequency offset applies to ALL of the simulated signals in the signal generator mode, i.e. once you set an offset, the code phases of the simulated signals start to shift compared to each other.

Start time

The Start time can be a set time, or the current time derived from an NTP server, as specified in your Network Configuration. If the current time is used, provided by an NTP server, the scenario start will be delayed, in order to allow the simulation to load required data, and start aligned to the nearest GPS minute.

The NTP (UTC) timescale is converted to the GPS timescale by a UTC-GPS offset defined in the firmware.

For more information, see Start Time.

Note: If this field is grayed out, it is not applicable for the chosen configuration.

Ephemeris

If NTP start time is used, the Ephemeris cannot be downloaded, as this data is not available in real time. The simulated range equals to (25.0E-3*speed_of_light), so the 1PPS Out from the back panel would trail the time mark determined from the RF Out signal by 25 ms.

Note: If this field is grayed out, it is not applicable for the chosen configuration.

AutoStart

If set to ON, AutoStart will start the Signal Generator mode automatically, once you powered up the GSG unit.

If set to OFF, the signal generation is started by pressing the START key, and stopped by pressing CANCEL. When a signal is generated, the simulated GPS time and the text Transmission ON are displayed (see illustration below).

Note that Power and Frequency offset can be edited while the transmission is ON.

Signal Generator running

All signal parameters are stored to non-volatile memory and are set when the unit is started.