• The appearance of the table and the meaning of the band start and stop sometimes cause confusion. The band start and stop do not define the frequencies that you must sweep over, but rather define the range where the given set of equations will be applied. Thus multiple bands can be created with a different equation set for each. When multiple source is ON, the system frequency (i.e., that set on the frequency menu or the segmented sweep screen) must be between the band 1 start frequency (or equal to it) and the last band entered stop frequency (or equal to it). If the Frequency menu range was outside the multiple source range when editing started, when DONE EDITING is hit (or multiple source turned on if it was off), the start and stop frequencies will be coerced to the multiple source band range. One can always sweep any range within the span that has been defined.

• Activation of external synthesizers can sometimes be mysterious and part of this is related to the limitations in constantly polling the GPIB bus. To avoid a slowdown in sweep time, the bus is only polled when entering multiple source or the ext. source submenu (and certain other times related to mm-wave modes). Thus the sources must be connected at their correct addresses (and of course turned on) when the menu is entered in order for it to be visible. If multiple synthesizers were connected and were accidentally set to the same address, it may be necessary to set the addresses correctly and then cycle power on the synthesizers for the bus communication to recover. Also do not forget to connect the 10 MHz references (often the VNA acts as the 10 MHz master, but this is not required).

• When an external synthesizer is under remote control by the VNA, sometimes the display of the synthesizer will still show an old frequency (this depends on firmware revisions and the model of the synthesizer). This may not correspond to where the synthesizer actually has been programmed. That can best be verified with the VNA measurement itself or with a spectrum analyzer. The power readout, if present, will update real time and this is another way to check if control has been established (by changing the entry on the external source submenu of the Power menu).

• Complete control has only been established for the MG3690B (and beyond) and MG37022A synthesizers. Certain older Anritsu and Wiltron synthesizers will work under some frequency plans, but may not always work due to frequency resolution differences.

• On the Ext. Module Control dialog, the maximum VCO overrange defaults to 250 MHz (this is the amount of overrange allowed on the base 2.5-5 GHz VCO, thus at the 20 GHz plane, it translates into 2 GHz), but this amount may not always be available depending on temperature and other variations. If one is using a lot of overrange and lock errors are visible on the message bar, the frequency plan of the setup should be re-arranged to require less overrange.

• When using RF leveling, less control range is available than when using IF leveling (only applies to the 374x modules) due to lower dynamic range detection. The IF leveling only works well when the net IF is less than a few hundred MHz so it can work well for IMD measurements, but not so well for mixer measurements. RF leveling should be used for the latter. Two separate factory ALC calibrations are performed (one using each detector path) so reasonable power control should always be possible.

• The common offset selection (Ext. Module Control dialog) is valuable for high order multiplied measurements as has been discussed, but requires the base receiver and source (referenced to a 5 GHz plane) to be within about 80 MHz of each other. Thus at a 20 GHz max frequency plane, they must be within about 320 MHz. If lock errors are observed, consider unchecking this box.