What type of signal is radiated by the back course?

The back course signal is specifically associated with the lateral guidance provided to an aircraft during an approach to landing, particularly when utilizing a Instrument Landing System (ILS). This signal is known as a reverse sensing signal because it allows pilots to navigate the aircraft back along the extended centerline of the runway when flying the back course of an ILS approach.

When flying the back course, the navigation system provides guidance that is opposite to what is provided on a forward course, hence the term "reverse sensing." Pilots must understand that when they are on the back course, if their indications show that they are off course to the right, they actually need to fly left to align with their desired path towards the runway, and vice versa. This understanding of the signal's nature helps ensure safe and accurate landings.