Instrument Function > RF Block > Phase > Phase Continuous Frequency
Phase Continuous Frequency

The phase continuous mode can be enabled in the "Phase Continuous Frequency Settings" section of the "Frequency" dialog. In this mode, the output sinewave is phase continuous, that means there is no phase discontinuity or glitch when changing the frequency.

At the transition from one frequency to another an intermediate frequency (switching transient) occurs, which causes spurs (see figure below). The transient is due to changes of the synthesizer settings (e.g. dividers, filters, phase detectors).

Transition for a 1 kHz step at 1 GHz without phase continuous mode active. For the graphical display the signal is down converted into the kHz range.

The phase continuous mode freezes the settings of the synthesizer (for example dividers, filters, phase detectors) which could generate phase discontinuities when changed. The frequency change is effectively performed by changing the fine resolution synthesizer. This allows a phase continuous change from one frequency to another without any transients (see figure below).

Transition for a 1 kHz step at 1 GHz with phase continuous mode active. For the graphical display the signal is down converted into the kHz range.

The available frequency range for phase continuous settings is limited by the fine resolution synthesizer used and varies with the RF frequency setting at the point of activating the phase continuous mode.

Depending on the instrument equipment - with or without option R&S SMA-B22 - the fine resolution synthesizer used is a DDS (Direct Digital Synthesizer, with option R&S SMA-B22) or a Fractional N-Synthesizer (without option R&S SMA-B22). The DDS provides generally a wider frequency range for phase continuous settings. In addition, two modes (narrow and wide) allow a selection either in favor of higher signal quality or in favor of an especially wide frequency range.

When phase continuous frequency setting is active, data sheet values no longer apply

Activating frequency or phase modulation deactivates phase continuous settings and vice versa.

Setting a Phase Continuous Frequency Sweep
  1. In the "RF Frequency Sweep" Menu, if the sweep is active, switch it off.

  2. In the "RF Frequency" Menu under the "Phase Continuous Frequency Settings" dialog

    1. If the "Phase Continuous Frequency Mode" is Active, switch it off

    2. Set "Frequency Range" to “Narrow”

    3. Select the RF frequency

    4. Check displayed Frequency Range

    5. If the "Frequency Range" corresponds to the selected frequency range, check the "Phase Continuous Active" box

    6. If "Frequency Range" in Narrow Mode does not, select “Wide” for the Frequency Range and check the Phase Continuous Active box

  3. In the "RF Frequency Sweep" dialog

    1. Modify the "Start Freq" and "Stop Freq" or "Center Frequency" and "Span" as needed.

    2. Set the RF frequency sweep State to “ON”.

Optimum user settings for the phase continuous frequency sweep

In the "RF Frequency Sweep" dialog there are some settings that will improve the phase continuous sweep results for both "Narrow" and "Wide" mode choices.

  1. "Step Lin": low step size

    In order to get the best spur performance during frequency change, it is recommended to reduce the step size and (if necessary) increase the sweep speed by decreasing the Dwell Time. Effectively, the sweep will be performed in the same amount of time, but with smaller step sizes.

  2. "Shape": Triangle sweep

    The triangle sweep offers a uniform forward sweep and return to the beginning frequency. The saw tooth sweep produces a uniform forward sweep with an abrupt reset to the starting frequency. The abrupt reset can generate spurs.

 


Imprint | Statement of Privacy | Terms & Conditions© 2016 ROHDE & SCHWARZ