Some quantitative experiments in long-distance radiotelegraphy
L.W. Austin · Bulletin of the Bureau of Standards · 1911
During December, 1909, and the spring and summer of 1910 the Navy Department carried on long-distance wireless tests between the scout cruisers Birmingham and Salem and the large Fessenden station at Brant Rock, which was leased by the Government for this purpose.These tests were primarily for the determination of the range of communication between the two cruisers and between the cruisers and the Brant Rock station.The United States Naval Wireless Laboratory had charge of the taking of certain quantitative measiurements in connection with these tests, and this enabled us to obtain scientific data in regard to the laws which Austin] Experiments in Long-Distance Radiotelegraphy 317 meters, and 0.018 microfarad at 1000 meters wave length.The motor generators were 500-cycle machines rated at 10 kilowatts, and the spark gap was of the same type as that used at Brant Rock but of smaller dimensions.JULY EXPERIMENTS Ig.Sending antenna current in amperes.Ik-Received antenna current through 25 ohms.N. Night observations.K. Received antenna current at i kilometer distance.d.Distance in kilometers.h.Height of flat top antenna.a. Day absorption coefficient = 0.001 5. X. Wave length.H. Stat.Heavy static = atmospheric discharges preventing re- ception of signals.Miles.Nautical mile = 1.85 kilometers.For good communication.Ir =40X10"^amperes through 25 ohms =4 X io~^watts.For audible signals.Ir = 10 X io~^amperes through 25 ohms = 2.5 X 10 "^w atts.Preliminary experiments were begmi early in July, the scout cruisers lying at anchor in the harbor at Provincetown, 22 miles from Brant Rock.The path of the waves between the ships and the shore station, except for a narrow strip of sand hills boimding Provincetown Harbor, lay entirely over water.Later, when tha ships put to sea, it was found that this strip of land made no appreciable difference in the received signals.Careful measurements were made on the intensity of the received antenna current at Brant Rock for the two wave lengths i 000 meters and 3 750 meters.This ciurent was measured either by means of a hot- wire ammeter of 15 ohms resistance, provided with a mirror for mirror and scale readings,* or by a tellurium constantan thermo- element,^also of 15 ohms resistance.The hot wire ammeter gave a scale deflection of about 0.2 millimeter for i milliampere oscil- latory ciurent in the antenna and 9.4 millimeters for 10 milliam- peres.One millimeter galvanometer deflection with the thermo- element was equivalent to 263 microamperes, and the deflections ^L.W. Austin, Electrical World, 49, p. 308; 1907.