Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

A PRETUNED TURNSTILE ANTENNA*tByGeorge H. Brown and J. EpsteinResearch Department, RCA LaboratoriesPrinceton, N. J.Division,Summary— Electrical and mechanical design refinements provide anultra-high-frequency unit that can be adjusted before being erected. Elementsare directly grounded for lightning protection and heaters are providedto prevent icing.VT)f ^HE purpose of this paper is to describe a new turnstile antennadesign for ultra-high-frequeney broadcasting.The original turnstile 1 was so constructed that the elementswere fed by means of open wires twisting around the supporting mast.Adjustment of the phase relationships and current magnitudes wasaccomplished by means of two properly matched transmission lines cutto the proper lengths and combined in a common terminal. The adjustmentof these lines at the base of the antenna proper was rathercritical and involved a certain amount of patient effort.With the advent of frequency modulation on the ultrahigh-frequencies,the turnstile antenna found many applications. It soonbecame apparent that many antennas would be placed on the topsextremely tall supporting structures, where the matching and phasingadjustments become very difficult if not impossible. With these factorsin mind, the development of a new type of turnstile was undertaken.2The most important feature of the new antenna isofthe fact that itis completely pretuned during the fabrication of the individual elementsso that no work of an engineering nature is necessary to putthe antenna into operation.The 90-degree phase relation is accomplished in the construction ofthe antenna elements themselves, so that no adjustments at the base areneeded to obtain the circular pattern.The antenna elements are so constructed that, while acting as insu-* Decimal Classification: R321.32.f Reprinted from Electronics, June, 1945.1 Brown, George H., "A Turnstile Antenna for Use at Ultra-High-Frequencies," Electronics, Apr. 1936.2Brown, George H., and Epstein, J., "A Turnstile Antenna for Ultra-High-Frequency Broadcasting," presented at the I,R.E. Summer Convention,Detroit, Mich., June 23, 1941,178