One 900mhz receiver is required at each wireless instrument location.
A single receiver can collect transmissions from as many transmitters as your system includes. That is, one receiver will serve all wind, temperature and rainfall transmitters within a 300' radius.
If you wish to install instruments in different rooms, you will need one receiver for each location.
The wireless receiver should be located in the wall behind the instrument display, and powered by any of the AC adaptors used to power a wireless instrument.
Dimensions of the wireless receiver are: 3.74"L x 2.25"W x 1"H