L 502 ] 



LYIII. The Reception of Wireless Waves on a Shielded Frame 

 Aerial. By Alan A. Campbell Swtnton, F.li.S* . 



TflE following experiments were recently carried out by 

 the writer in bis laboratory in London, in order to test 

 a suggestion made by Mr. N. P. Kinton, a member of the 

 Sub-Committee on Directional Wireless of the Radio Research 

 Board, that something of the nature of a wireless telescope, 

 with improved direction-finding properties, might be made 

 by placing a frame aerial in a large metal tube or wire 

 spiral, open at the ends. 



Particulars are published with the permission of the Radio 

 Research Board. 



The frame employed was a eircuhfr one, 1 foot in diameter, 

 with 100 total turns of No. 20 S. W.G. cotton-covered copper 

 wire, all the turns bunched together, with a four-way switch 

 so arranged that the number of turns in use could be 

 diminished to 20, 40, or 80 turns, as desired. 



With 80 turns in use, and with an adjustable condenser 

 connected across its ends, this frame records, in London, 

 the spark emission from the Eiffel Tower in Paris, loudly 

 when coupled to a 5- valve resistance amplifier connected to 

 a 3-valve transformer-coupled note magnifier, and has fairly 

 oood directional properties. All the experiments were made 

 with the spark emission from Paris, which has a wave-length 

 of 2600 metres. 



The shielding tube first employed consisted of an oblong- 

 wooden frame of square section, ] 8 inches wide, 1<5 inches 

 deep, and 4 feet long, wound round with No. 18 S.W.Gr. 

 bare copper wire spaced 1 inch apart and connected to earth. 

 With the ends of the tube open, and with the extremities of 

 the square copper spiral unconnected, the frame, when placed 

 within the tube, gave signals from Paris of approximately 

 the same strength as outside of the tube. When, however, the 

 ends of the spiral were connected together, so as to form a 

 closed circuit, the signals received on the frame were con- 

 siderably weakened, say by about 50 per cent. ; and this 

 weakening was accentuated, so that the signals only retained 

 about 25 per cent, of their original strength, by short- 

 circuiting the individual spirals with four longitudinal 

 copper wires along the corners of the tube. It was found, 

 however, that the tube itself possessed no appreciable direc- 

 tional screening effect upon the frame, it making no detectable 



* Communicated by the Author, having been read before the British 

 Association September 1921. 



