Apex radio stations (also known as skyscraper and pinnacle) was the name commonly given to a short-lived group of United States broadcasting stations, which were used to evaluate transmitting on frequencies that were much higher than the ones used by standard amplitude modulation (AM) and shortwave stations. Their name came from the tall height of their transmitter antennas, which were needed because coverage was primarily limited to local line-of-sight distances. These stations were assigned to what at the time were described as "ultra-high shortwave" frequencies, between roughly 25 and 44 MHz. They employed amplitude modulation (AM) transmissions, although in most cases using a wider bandwidth than standard broadcast band AM stations, in order to provide high fidelity sound with less static and distortion. In 1937 the Federal Communications Commission (FCC) formally allocated an Apex station band, consisting of 75 transmitting frequencies running from 41.02 to 43.98 MHz. These stations were never given permission to operate commercially, although they were allowed to retransmit programming from standard AM stations. Most operated under experimental licenses, however this band was the first to include a formal "non-commercial educational" station classification. The FCC eventually concluded that frequency modulation (FM) transmissions were superior, and the Apex band was eliminated effective January 1, 1941, in order to make way for the creation of the original FM band, assigned to 42 to 50 MHz. Initial development During the 1920s and 1930s, radio engineers and government regulators investigated the characteristics of transmitting frequencies higher than those currently in use. In the United States, by 1930 the original AM broadcasting band consisted of 96 frequencies from 550 to 1500 kHz, with a 10 kHz spacing between adjacent assignments. On this band, a station's coverage during the daytime consisted exclusively of its groundwave signal, which for the most powerful stations might exceed 200 miles (320 kilometers), although it was significantly less for the average station. However, during the nighttime, changes in the ionosphere resulted in additional long distance skywave signals, that were commonly reflected for up to hundreds of kilometers. Over time, technology was developed to transmit on progressively higher frequencies. (Although initially these were in general called "ultra-high shortwave" frequencies, radio spectrum nomenclature was later standardized, with 3 to 30 MHz transmissions becoming known as "High Frequency" (HF), 30 to 300 MHz called "Very High Frequency" (VHF), and 300 to 3,000 MHz called "Ultra High Frequency" (UHF)). It soon became