Pg. 222 covers device rating (which applies to drones). The sample table on page 222 lists drones as a DR 3, security vehicles as a DR 4, and Military vehicles as a DR 5. War! has a list of Military Vehicles/Drones, but it's up to the GM to determine what is classified as a Security vehicle for DR purposes.
What this means is that the drone is treated as having it's DR in all it's matrix attributes (unless you upgrade them per the normal rules provided). Response and Signal can both be upgraded up to twice I believe.
Pg. 334 refers to the range of Sensors, a drone's Signal attribute isn't increased by replacing sensors, replacing the sensors just determines how far the sensors can detect things and reach. To use the drone, you still have to be within the drone's signal range. It's complicated, but just few every single sensor, drone, and commlink as a separate Signal and it'll start to make sense.
It took me forever to find it to, so don't feel bad.