How to enable the B400 Silent Mode?

There are two options for activating Silent Mode;

1. Apply a voltage of between 2V and 30V to the SILENT P (Pin 7) and SILENT N (Pin 6) terminals of the 14 way connector. You will need to order an accessory cable for this. More details can be found in the B400 user Manual Page 32
2. Alternatively go to Menu ->System Settings ->System Information ->Enable features

enter SILENT
go to Menu ->System Settings ->Advanced ->Radio & Long range settings

There should now be a 'Silent mode' menu where you can enable/disable transmit. 

To remove the feature 

go to Menu ->System Settings ->System Information ->Enable features

enter SILENT