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Page:Popular Science Monthly Volume 89.djvu/637

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��Overcoming Troubles

in a 200-Meter

Wave Outfit

By R. H. G. Mathews

���The following article won the second prize of Fifteen Dollars in the POPULAR Science Monthly's Radio Article Contest. We would call it to the attention of wireless amateurs because it shows how, with a little ingenuity, a wireless amateur can overcome discouraging obstacles. We want more articles of this type. — EDITOR.

��WHEN the radio law of 1912 went into effect, many of the amateur operators of the United States dismantled their apparatus and gave up experimentation with wireless teleg- raphy, thinking that a station which complied with that law could not do successful work. "Successful work" at that time in the amateur field meant transmitting 30 miles, with an input of 2 to 3 Kilowatts. Many amateurs whose stations comply with the present law, are now able to work over distances of from 800 to 1,000 miles with less than one Kilowatt input. To do this long distance work, using a short wave and low power, requires specially designed apparatus. A minimum of condenser with a maximum of inductance must be used in the closed oscillating circuit.

In order to obtain this condition, I designed and built a 43,000-voIt, i-Kilo- watt, closed core transformer. Because of the use of this extremely high \-oltagc, a condenser consisting of only 358 sc]. in. of conducting surface, on opposite sides of \i-\n. plate glass sheets, is used. With this small condenser capacity, the prim- ary inductance which may be used on a short wave is quite large, and con- sequently an easy transfer of energy from the closed to the open circuit is obtained.

��At first, I made my condenser of the usual packed type, suspended in a tank of oil. I found, however, that my plates were continually puncturing, due, I thought, to my excessive voltage. I eventualh- discovered that the breakage was caused, not by direct puncturing, but by what appeared to be a crushing of the glass by a force exerted on it by the attraction of the charges of opposite polarity on opposite sides of each glass plate. When the plates were clamped

��GLASS- PLATES

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��CONTACT STRIP

TANK CON- TAINING OIL

��RACKTOHOIO PLAItSAMRI

��Fig. 1. Method of spacing plate glass sheets to eliminate breakage when im- mersed in tank of transformer oil

together the crushing strain exerted in- this force was tremendous. I entirely eliminated this breakage by spacing

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