The BSL450U differs from the BS450U in the size of the radome. the "BS" Series has a 1" (254mm) diameter radome and the "BSL" has a 1.5" (381mm) diameter radome.
The BSL450U Base Station Antenna is rated at 250 watts with Unity gain from 450-470 MHz.
The radiating elements are constructed of copper & copper alloy. They are encased in a fiberglass radome for total environmental protection. Weatherproof: The fiberglass radome is ultraviolet inhibited. The heavy wall aluminum mounting sleeve is epoxy coated for superior weather protection.
For more details see the BSL450U Data Sheet.