FAQs from Rohde & Schwarz

External reference locking range


I have found two informations reagarding the external reference for my signal generator. One is the frequency locking range in the specifications.

Input for external reference

Connector type REF IN on rear panel BNC female
Input frequency 5 MHz, 10 MHz
Frequency locking range ± 3 × 10^-6
Input level range 0 dBm to +16 dBm
Input impedance 50 Ω (nom.)

The other one is the synchronization bandwidth in the manual.

Synchronization bandwidth
Selects the synchronization bandwidth for an external reference signal.

  • "Narrow": Synchronization bandwidth is 50 Hz.
  • "Wide": The synchronization bandwidth is approximately 350 Hz. This mode is useful for very precise reference sources of high spectral purity.
  • Remote command: [ :SOURce] :ROSCillator:EXTernal:SBANdwidth on page 809

What is the difference between these two?


The frequency locking range from the specifications is the actual area where the reference frequency can be located so the generator is still able to lock to the external reference.

So for an external reference frequency of for example 10 MHz the max. deviation the generator is still able to lock to is +/- 30 Hz.

Whereas the Synchronization Bandwidth is the maximum update rate of the generator in order to still lock to the external reference. That means if the Synchroization Bandwidth is set to "Narrow" the maximal update rate is 50 Hz. If the external reference frequency changes faster the generator will not be able anymore to lock to this reference.

When set to "Wide" the generator is still able to lock for an update rate of up to 350 Hz. But for that setting the reference frequency needs to be a very precise signal with high spectral purity.

In order to lock to the external reference both conditions have to be fullfilled.

Specifications of the SMBV100A: