Large Radar System
General Information 
Each Long Radar adds one unit to your bases's "Long Range Detection" meter, and helps with UFO Detection.
Every thiry minutes game time, each Large Radar has a 5% chance of detecting a UFO within a 450 nautical mile radius of your base. If you advance the time an hour or day at a time, it will make multiple checks and interrupt if a UFO is detected, setting the time to be at whatever point the detection happened (even if it is only five seconds after the last update).
Whether these chances are effected by the size of the UFO is unknown. Popular opinion is that multiple radar systems do not add to these odds. (?)
Statistics
Construction Time: 25 days
Construction Cost: $800,000
Maintenance Cost: $15,000/month
Detection Abilities:
Short: +20
Long: +20
Hyperwave: 0
The above apply a one-time-bonus to the base's detection abilities.