Oregon Consoles have a gated 433 Mhz receiver in them to save battery power, as most consoles are designed to run off batteries.
The Oregon sensors all transmit at fixed precise times using an internal 32768 Khz watch crystal .
The sensors have to be synchronised initially with the console before they will be recognised and then the console knows when to expect incoming transmissions.
Usually, the synchronization is done by pressing a reset button on the console which turns the receiver on for around 5 minutes which is long enuf to pick up any nearby sensors.
If however, the console wont pick up your sensor in the 5 minutes, then something else is the problem.
Ive no experiance with V2.1 sensors.