The latest generation of the R&S SMA provides an extended SynEx RF assembly which improves the phase noise performance. It is achieved by reducing the PLL bandwidth of the main synthesizer (see "Main Pll Bandwidth") for a certain frequency range and offset.
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The phase noise performance for frequency offsets higher than 100 kHz is improved in the narrow PLL bandwidth mode (blue measurement curve). In the offset range 10 kHz to 100 kHz, the pedestal phase noise deteriorates.
If you generate a frequency- or phase-modulated RF signal, you can also set the narrow PLL bandwidth, provided you perform the modulation in "Low Noise" mode. Consequently, some operation modes exclude each other.
The table shows the operating modes which can be activated simultaneously (+) or which deactivate each other (-):
Main PLL Bandwidth | FM Mode "Normal" | FM Mode "Low Noise" | ɸM Mode "Low Noise" | ɸM Mode "High Bandwidth" | ɸM Mode "High Deviation" |
---|---|---|---|---|---|
Normal | + | + | + | + | + |
Narrow | - | + | + | - | - |
When you enable a mode, while another excluding mode is already active, the R&S SMA automatically adjusts the parameters of this previously set mode. Consequently, the instrument always performs the signal generation with the current settings and adjusts the foregoing settings accordingly, if required.
A message in the info line indicates when there is a conflict between the modulation mode and the PLL bandwidth setting.
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