The Keysight 8761B SPDT Coaxial Switches are not listed in the "Keysight 34945A, L4445A and L4490A/L4491A Configuration Guide". Why?

The Keysight 8761B coaxial SPDT switches utilize a two-terminal dc connection for position control. Switch path selection is achieved and toggled by reversal of the DC polarity across these coil terminals. The following excerpt from the "Keysight 8761A/B Microwave Switches Technical Overview":

To change the state of the switch requires a reversal of the voltage polarity for at least 20 milliseconds. 
 

8761B Coil Connection Schematic (NOT supported by the 34940A / L4445A / L4490A / L4491A)4490A / L4491A)

Conversely, for other ‘supported’ coaxial switches the 34940A / L4445A / L4990A / L4491A achieve switch control by providing a constant positive dc supply (typically +28Vdc) to the positive common coil input connection. Supported SPDT switches, such as the Keysight N1810 Family, then employ a dual coil control where the path selection is engaged by closing coil’s ground connection. The following excerpt from the "Keysight N1810/1 /2 Coaxial Switches Technical Overview":

There are two positions for the N181x family of switches. Standard switching is accomplished by applying the supply voltage to pin 5 (+V) and grounding either pin 4 (A) or pin 3 (B) to actuate the mechanism to the desired state.

 N1810TL Coil Connection Schematic (supported by the 34940A / L4445A / L4490A / L4491A)

Additionally, the Keysight 8761A SPDT coaxial switch is not supported by the 34940A / L4445A / L4490A / L4491A. The Keysight 8761A employs dc polarity reversal equivalent to the 8761B but differs from the 8761B in that the coil voltage requirements are 15Vdc.

Learn more about Keysight Single-Pole Double-Throw Switches - SPDT