Multi-station Site Work began in 1950 on the multiple TV/FM antenna installation. Many engineers were involved in the research, design, testing, and construction of the multiple array. Among them were Dr. Frank G. Kear (Kear and Kennedy), John B. Dearing and Herman F. Gihring (RCA), and 0. B. Hanson and Raymond F. Guy (NBC). Prior to initial construction of this new antenna structure, the American Broadcasting Company had moved its transmitter to the Empire State Building and utilized an antenna at the lop of the NBC supporting mast. Later in the year, during construction of the multiple-antenna structure, ABC's WJZ-TV (now WABC-TV) used an interim antenna mounted atop the mooring mast but tilted 15 °. from vertical. The NBC station did the same, for mutual isolation. By December 1951, work was completed on the multiple-antenna installation. It was designed and built so that each of the five television and three FM stations could employ the maximum radiation permitted by the FCC. As shown in Fig. 3. the tower becomes progressively narrower as its height increases. This construction was dictated by the principles of good mechanical design. Since the wavelength and consequently element size, decreases with increasing frequency. the antennas were generally arranged for increasing frequency with increasing height. The NBC antenna was an exception to this rule for two reasons: As original tenant at Empire State, NBC had prior rights to position on the tower, Also. since NBC chose a superturnstile antenna, it had to he on lop, the slim steel pole would not support additional antennas above it. In addition to handling the signals of five television stations, the tower was designed to radiate transmissions from three FM stations. The NBC FM transmitter output was triplexed into the NBC TV antenna, The ABC and CBS FM signals were diplexed into a single set of dipoles installed within the CBS TV antenna near the bottom of the tower. In June of 1951, WNBT began transmissions from its antenna on the tower. In August, WPIX (channel 11) and what is now WABC-TV (channel 7) started using their facilities on the structure, WABD (now WNEW-TV. channel 5) joined the other stations in October, and WCBS-TV (channel 2) was operating from its new facilities by December. The ABC and CBS FM stations began operating from their common antenna in March of 1952. With five of the then existing seven New York metropolitan area TV stations transmitting from the Empire State Building, the trend soon reached the other two. In 1952, WATV (now WNDT. channel 13), began transmitting from an antenna mounted on the mooring mast of the building. An additional installation was made during 1953, and in, December WOR-TV (channel 9) began transmission from an antenna at the top of the mooring mast, just below the multiple-antenna lower. Sister station WOR-FM followed in 1956, utilizing an antenna just below the base of the multiple-antenna tower. In 1958, WNEW-FM began operation from an antenna within the WNEW-TV array. When, in 1961, the FCC planned a test of UHF television in a metropolitan area. the Empire State Building was chosen as the antenna site. For the first (and so far only) lime in Its history, the Commission itself became a broadcast licensee. WUHF started transmitting November 1, 1961 from an antenna located on the four corners of the tower, beside the WCBS-TV array, near the tower base. The station (on channel 31) was later donated to the City of New fork and became WNYC-TV. By 1965 a ninth TV station had come on the air in the New York 'areaWNJU-TV (channel 47) licensed to Linden. N. J. It began transmitting May 16, 1965 from an antenna on the mooring mast of the building. Combined FM Operations By the fall of 1959, nearly 20 FM stations were operating in New York City. With five stations already transmitting from Empire State and six others expressing an interest in using facilities on the building, the possibility of a commonly shared FM antenna arose. Rather than simply tack on antennas one by one. it seemed advantageous to investigate the possibility of a master antenna. The Empire State Building Co. asked Dr. Kear for an opinion on the possibility of a master FM antenna. He recommended a feasibility study which was undertaken by Alford Manufacturing Co. Dr. Kear and his associates then begun design, in conjunction with the testing and construction of several scale models by Fred Abel. Andrew Alford, Harold H. Leach, and Nelson R. Powers, all of Alford Manufacturing Co. In March of 1965, three New York FM stations agreed to lease space on the proposed master FM antenna, shortly thereafter, construction of the array was begun by Alford Manufacturing, As can be seen in Fig. 4 and the other photos, space on the mooring mast was limited. The best available location seemed to be the stainless-steel bands surrounding the 102nd-floor observation deck. Through [the use of a scale model, various combinations of 8, 12, and 16 dipoles were tried, until tests proved 16 to be the optimum number for each bay. This configuration provided the required circularity in the horizontal plane together with a VSWR of less than 1.10 to 1 from 90 to 108 MHz and less than 1.20 to 1 from 88 to 90 MHz. One of the dipoles is seen in Fig, 5. Dual polarization was incorporated into the antenna by orienting each dipole 45° away from the horizontal. Each dipole is fed 22.5° out of phase with respect to its neighbors; this arrangement was found to give satisfactory patterns and a low standing-wave ratio. The dipoles are arranged into groups of four, each group being fed by one element of a four-way fork. Each bay contains 16 dipoles, and there are 2 bays, A transfer panel allows feeding both bays, or either bay in case of an emergency Each station is connected to the antenna through a multiplexer which offers a high degree of attenuation to all frequencies except that of the input station. All multiplexers arc connected in a line and beyond the last station is an extra, unmultiplexed input. If any station's multiplexer should be put out of service, that transmitter may he coupled to the last input for emergency operation. Normal isolation from transmitter to transmitter varies from 26 to 55 dB. The antenna will accommodate 17 stations of up to 10 KW. On December 9, 1965, WQXR-FM became the first station to begin transmitting from the master FM antenna. During 1966, seven more stations installed transmitters in the building and used the master array: January. WHOM-FM: February. WLIB-FM and WOR-FM; March, WBAI and WNCN; September, WNYC-FM and WPIX-FM, On February 1. 1967 WRFM became the ninth station to transmit from the master FM antenna.