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DID YOU KNOW . . . . . . . . ?
The vertical antenna referred to as the ”5/8 whip,” commonly used as a 2-meter mobile antenna was originally developed to fill a need for an efficient transmitting antenna in the AM broadcast band. The first broadcast antenna designs used a top loaded vertical type of antenna. Usually this vertical was lower that a ¼ wavelength and was supported from a number of top loading wires strung between two towers. There was no radiation from the horizontal top loading wires because of the canceling effects of opposing current flow.
Besides physical support, the horizontal wires served to electrically lengthen the vertical element as a means to bringing it near a quarter wavelength. This type of antenna structure certainly had its drawbacks. In areas where there was heavy ice loading, the large number of conductors and leverage on the supporting structures frequently caused severe damage. The radiation pattern was distorted by two supporting towers.
A paper published in the proceedings of the IRE, December 1924, “On the Optimum Transmitting Wavelength for a Vertical Antenna Over Perfect Earth” described the findings of Suart Ballantine. He had determined that a vertical radiator of 0.64 wavelength produced maximum radiation horizontally broadside to the antenna. In his paper, Ballantine calculated that in comparison to the zero gain of a quarter-wave vertical, the 0.64 wavelength antenna produced a gain of 3.03 dB.
One problem in the broadcast application became apparent with the first installations. Radiation from the higher angle minor lobe returned to ground from the ionosphere at night, and caused severe fading several miles from the transmitting point by interfering with ground wave major lobe. The solution was reduction in antenna height to 0.528 wavelength. Ballantine’s later developments in ground radial systems further improved the efficiency of broadcast vertical type antennas. To this day, despite the widespread shift to the FM band there are still thousands of AM broadcast stations using 190 degree towers.
Stuart Ballantine who was born in 1897, made many important contributions to the science of radio. In 1922 he wrote “Radio Telephone for Amateurs.” Fully indexed, it dealt with basic theory, vacuum tube theory, RF stages, various modulation methods systems and antenna systems. Published as a hard cover volume, it was a major treatise for its time and set a precedent for comprehensive radio publications that followed, such as ARRL’s “Radio Amateur’s
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Charles Stuart Ballantine
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Handbook” launched four years later.
The author of this column has a hardback edition of Ballantine’s text that his father purchased in 1924. It is an intriguing insight into the state of technical advancement in that period, Ballantine’s extensive technical knowledge and his unique manner of presentation. Ballantine had a very distinguished career. He was born in 1897 and by 1908 was an Amateur Radio enthusiast. He worked as a ship radio officer during the summers of 1913-15. After graduation from Drexel University, he began his engineering career with the US Navy and was instrumental in achieving several advancements in direction finding and developments in the loop compass. After WW1 he attended Harvard and went on to foster many significant advances in the radio and audio field. He held more than thirty patents and was a Fellow of the American Physical Society, the Acoustical Society of America and the IRE. He received many prestigious awards from major organizations and the Franklin Institute named a medal in his honor. Ballantine died in 1944 at the age of 47. –VE1WG
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