 The WSR-1 to 4 series, the first operational weather radar in the United States, used the AN/APS-2F electronics, including a superheterodyne receiver, but with a larger antenna.As time progressed and experience with the original design increased, the Weather Bureau felt confident enough to upgrade the WSR-1 to WSR-1A, eventually finalizing on the WSR-3 and WSR-4 model.The WSR-4 upgrades included the removal of the original aircraft-oriented antenna in favor of a larger antenna, and the addition of a power converter such that it would now have the ability to function on conventional power.