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 obstructed path for the radio waves, passing over the Catskill foothills.



The short waves used have extremely high frequencies, a five-meter signal representing approximately 60,000,000 cycles a second. A four-meter wave would have a frequency of 75,000,000 cycles. In the 15,000,000-cycle space between four and five meters, every radio station now in use—amateur, naval, broadcasting and commercial—might be operated without interference from overlapping signals. It is that enormous number of possible wave channels in the low waves that promises to revolutionize wireless. Experience has shown that a separation of at least ten kilocycles, or 10,000 cycles, is necessary between near-by stations. On that basis there are between 200 and 550 meters—the broadcast wave band—only some ninety possible wave channels, though they cover a 350-meter band, while the single one-meter band between four and five meters contains 1,500 wave channels.

The experiments are continuing, to determine the usefulness of the short waves in broadcasting over fairly limited distances. Radio engineers have been aware for some years that short waves are best for long-distance transmission. One of the interesting facts already learned is that the short-wave bands are practically free the year around from natural static, but that man-made static, such as that caused by the ignition system of a passing automobile, is particularly noticeable.

 



By making various alterations in a familiar brand of tractor, an efficient engine has been afforded the guardians of a California forest to help combat fires. It has a six-speed transmission, pneumatic tires, a three-speed pump, reels of hose and, on the trailer, a tank holding 520 gallons of water. This may be used while the hose is being led to a creek or other natural supply. A particular advantage of the outfit is that it can climb steep grades. In a recent test, one of the tractor engines was driven 215 miles over mountain roads in ten hours. When the destination was reached, the trailer was disconnected from the tractor and a plow attached, making a firebreak up a thirty-percent grade in low gear.

