OCR Text |
Show Many Objects Arc. in j Path of Radio Waves j Experiments, undert ukeii by the lm- , renn of standards to determine the effect ef-fect of buildings, bridges, trees, etc, on radio waves have ImI lo the con- j clu.-.lin Ihi-it tiny 'one of these objects. I when interposed be'rv. ee.n the . trans-'! lnlttiiig aiirl receiving stations army cause the "Wave to 'deviJno ifrom a ' Ktraitlil eoiirs'e. Smh distortion of the wave mny nr Tm.y not alt'eet 'the lro:iciist 'lishmer appreciably, but tn'!--l 'be iP'ob'linl ns ter :is possible In the Use of direction finders. 'The .illrociion Under bus he-: come -of :liiiiortance In tho guidance of ships at sou imil conLaiil igiliinee has been pl-.icticed for the determination determina-tion of errors which may develop from I lie position of objects surrounding surround-ing these compass stations, rendering them uii dependable. The effects of trees and other objects ob-jects were disclosed by a portable direction di-rection finder which was placed in different positions around objects which were suspected of distorting effects. Signals from a transmitting set severt.l miles away on a number of different, wave lengths were used for caiilo-aiioil. A tree in. fili Open field produced no error in direction of the transmitter when the hp of the dlrettiou tinder was placed either directly in fro.it or behind it. To either side, the deviation devi-ation was as much as five degrees. A large screen of galvanized Iron, 17 by 10 feet, caused but slight distortion, dis-tortion, but evidenced a slight reradi-ufion reradi-ufion of waves. water lower with power lines nearby produced distortion, distor-tion, indications were that the power wires caused a large part of the distortion dis-tortion at longer wavelengths. A 7"i-foot 7"i-foot overhead antenna did not produce pro-duce any distortion, but wten the receiver wiis placed close to the lead-in lead-in the deviation was marked. The direction tinder for these tests consisted of a loop four feel square wilh provision for waves of -100. tVJo and 3,400 meters. The coils consisted of o turns, l.n centimeters apart ; 8 turns, .0 centimeters apart and '1 turns, .", centimeters apart. These coils were rotated on their axis by an observer, S foot away, by means of heavy cord. Visual observations were made In determining the direction of the transmitting station by means of a telescope mounted on the frame As a result of these observations t oopeers that thee s ind-l ion or leraoiaiion from most inetnlllc objects ob-jects so that a radio tlireetlmi Under placed hi the Imniedjiile vicinity gives I ;-.b erroneous OlKvlloii of the trans-! trans-! Initlii't' Millions. It Is always advis-i advis-i oliil'' to detune or open circuit nil) i wires in the vicinity of t he receiver lo prevent absorption or reradi. 'lion of 'lie waves, it being doubtful as to whether burying tlieni is sitllieieiit to avoid nil these effects. |