The most expensive facility in the game (but worth every penny), the Transmission Resolver not only picks up any Alien Sub within its detection range, but informs you of the type, mission, and race onboard. Resolvers can only be researched and built after you have researched Magnetic Navigation.
The Standard and Wide Array Sonars have a percentage chance of detecting any in-range Alien Subs with each sweep, but the Transmission Resolver will detect any Alien Sub within its range as soon as possible. Once this facility is constructed, all other sonar systems housed in the same base become unnecessary and can be dismantled.
With a detection radius of 2400 nautical miles, and automatic detection of alien craft, it is the ultimate tool for Alien Sub Detection. It adds one unit to your base's "Long Range Detection" meter, although that statistic is meaningless. Clearly there is no need for building more than one in any given base, even if there was it is likely that it would have no effect, as per the Sonar systems.
Construction Time: 26 days
Construction Cost: $1,400,000
Maintenance Cost: $35,000/month
The above apply a one-time-bonus to the bases detection abilities.