The MS4640A Series VNAs support up to four (4) External Sources.
External Synthesizer Connections
External synthesizers can be used when in multiple source mode. The control connections for a maximally configured multiple source scenario are shown here. All 10 MHz time bases can be linked, but this is not always required depending on the measurement.
It is important to note that the synthesizers are synchronized to the 10 MHz reference of the MS4640A Series VNA so frequency accuracy is maintained. External 10 MHz sources can also be used if they have at least the spectral purity of the VNA internal clock.
The GPIB connections are used for controlling the synthesizers and usual GPIB cable length practices apply. Note that the dedicated connector on the VNA is used. The synthesizer GPIB addresses must match those on the VNA external source address menu located at:
• MAIN | System | SYSTEM | Remote Interface | REMOTE INTER. | Ext. Sources | EXT. SRC ADDR.
The system will poll the GPIB bus for the external synthesizers periodically including when Multiple Source mode is activated and when the MULTIPLE SOURCE menus are accessed. To verify if a connection has been established, check the EXTERNAL SOURCE CONTROL menu to see if the State is Active.
• MAIN | Application | APPLICATION | Multiple Source Setup | MULTIPLE SOURCE | Ext. Src Control | EXT. SRC CONTROL
A connected source can be manually activated prior to entering data in the table to avoid having to re-enter the data, since data is only saved when Done Editing is selected. Flatness calibrations of external synthesizers may be available in certain versions of instrument firmware, in which case those buttons in will enabled.
If one or both synthesizers are turned off or disconnected while in broadband or mm-Wave modes, GPIB errors or sluggish system response may be experienced. It may be necessary to return to standard mode, reconnect/restart the synthesizers and then re-enter multiple source mode to continue. In extreme circumstances, it may be necessary to exit the VNA application, restart the synthesizers, and restart the VNA to establish communication.
External Sources Power Level
The power level of external sources is controlled by the External Source Power button on the main POWER menu as shown in the first part (left) of Figure: POWER and EXT. SRC POWER Menus. This leads to the power entry fields as shown in the second part (right) of Figure: POWER and EXT. SRC POWER Menus. Again, flatness calibrations may be available with certain firmware versions.
POWER and EXT. SRC POWER Menus
1. POWER [COUPLED] Menu and External Source Power button.
2. EXT. SRC POWER (EXTERNAL SOURCE POWER) Menu with settings for External Source Number and Source Power Level
Using the EXTERNAL SOURCE POWER menu, select the source with the top button, then enter the source power with the second button.
External Source Fast Trigger Mode
To enable or disable fast trigger mode when using MG3702xA external synthesizers, on the MULTIPLE SOURCE menu, click on the Ext. Src. Fast Trigger button which will bring up the dialog shown in Figure: EXTERNAL SOURCE FAST TRIGGER MODE Dialog Box. Select the desired mode (ensuring needed cables are connected) and click OK to effect the mode change.
