Instrument Function > RF Block > Reference Oscillator
Reference Oscillator

The R&S SMA is equipped with an internal reference oscillator that generates a reference frequency of 10 MHz. It is used as internal reference source for the synthesizer and the local oscillator. Alternatively, you can apply an external reference signal.

Regardless of the used reference source (internal or external), the R&S SMA always provides the configured reference frequency at the output. You can use it, for example to synchronize several interconnected instruments.

The settings of the reference oscillator are not affected by an instrument preset ("PRESET" key).

The following examples briefly explain the possible test setups and the settings to be considered.
  • Internal fref = 10 MHz (10 MHz REF OUT)
    Synchronizing a subsequent instrument using the internal 10 MHz reference signal of the R&S SMA

    The internal reference oscillator supplies the reference frequency.
    In addition, you can shift the frequency by an external tuning voltage within a certain range, EFC (External Frequency Control). This function is used, for example, in phase noise measurement systems.
    The frequency shift resulting from a tuning voltage value depends on the technical equipment of the instrument. See the data sheet for the associated technical data like sensitivity, input voltage range and impedance. The maximum bandwidth for external tuning signal input is approximately 50 Hz.
    Note: The bandwidth of an external PLL (Phase Locked Loop) used in a phase noise measurement system, must be less than the bandwidth of the external tuning signal input. If the measurement requires a higher bandwidth for the PLL, it is recommended that you use the external FM modulation (DC coupling) in low noise mode. The FM-DC mode yields a fixed tuning sensitivity that is independent of the RF output frequency and corresponds to the set FM deviation.
    Settings:
    "Source": "Internal"
  • External fref = 10 MHz (10 MHz REF OUT)
    If you have a clean external reference signal with 10 MHz frequency, you can directly pass it to the output. The signal quality remains the same.
    Synchronizing instruments by means of an externally applied reference signal having 10 MHz
    Settings:
    "Source": "External"
    "External Reference Frequency": "10 MHz"

    Set the additionally provided parameters, as for example the synchronization bandwidth according to the requirements of the application.
  • External fref = 5/10/13 MHz (5/10/13 MHz REF OUT)
    If you have an external reference signal with 5, 10 or 13 MHz, you can directly pass it to the output. The signal quality remains the same.
    Synchronizing a subsequent instrument an externally applied reference frequency of 5, 10, or 13 MHz
    Settings:
    "Source": "External"
    "External Reference Frequency": "5, 10 or 13 MHz"
Input and output connectors of the reference frequency

The appropriate connectors are located at the rear panel, see "REF IN" and "REF OUT".

To use the EFC feature, assign this signal at the "EXT TUNE" input connector at the rear of the instrument, see "Rear Panel Tour".

 


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