Page:Popular Mechanics 1928 01.pdf/4

 their great length. There are occasional exceptions, as when a near-by mass of metal, such as a gas holder, will block reception from a broadcasting station on its other side. The long waves bend as a rule around very large objects, just as visible light waves may be bent around atoms. On the basis of their comparative size, a house or office building is no more to the long radio wave than an atom to the fifty-thousandth of an inch light wave.

Because of their straight-line propagation and the shadow effect of interfering objects, unusual arrangements were necessary in the experiments with the five-meter waves. The transmitter, instead of being housed in a building or placed on the ground, was swung in the air from the top of a 300-foot aerial mast at Schenectady. An endless rope, running over a pulley on the condenser dial, made tuning possible from the ground, operating much like a chain hoist. The small output meter, fixed to the antenna, was read from the ground through a surveyors' transit. Wires dangling from the transmitter connected to the current supply on the ground.

The receiver used was a miniature "ham" set, consisting of regenerative detector and one audio amplifier. No antenna was necessary at the receiving end for the phone cords furnished wire to pick up sufficient energy. The tiny grid-tuning coil contained but five turns of wire, a half inch in diameter, and the tickler coil was a quarter inch long and a quarter inch in diameter, inside of the grid coil. Two very small condensers were used, and to keep the leads short, they were placed as close as possible together. They were so close, in fact, that, in order to use standard-size vernier dials, extension shafts were necessary. The condensers were placed at an angle to each other and a false end was built in the receiver cabinet to accommodate the angle of the dials.

Tests were first made over a distance of thirty miles. On top of a hill, with a clear "line of vision" to the transmitter, the signals came loud and clear, but as the portable receiver was carried down the far side of the hill and passed out of the straight-wave range, the signal faded and disappeared.



Following a survey of topographical maps for the country from Schenectady to New York city, arrangements were made to place the receiver on top of the Woolworth building, as the survey showed that, from its great height on lower Manhattan island, the transmitter atop its 300-foot mast at Schenectady would have an un- 