156 



Popular Science Monthly 



A Trussed Aerial Spreader 

 for Long Wires 



ALIGHT and strong spreader is very 

 desirable when the aerial reaches over 

 200 ft. in length. While bamboo answers 

 the purpose for spreaders shorter than 6 ft., 

 it does not do for longer ones. 



WIRE 



A light frame trussed so that it will 

 be strong enough to hold a large aerial 



A truss-built spreader fills the conditions 

 admirably. Select two straight-grained 

 pieces of spruce 9 ft. 3 in. long, by 1 in. 

 square and two braces 6 in. long by 1 in. 

 square. The pieces are assembled as 

 shown in Fig. 1. The detail showing how 

 the braces are fastened to the spreader- 

 piece on the side where the aerial wires are 

 attached is seen in Fig. 2. The other ends 

 of the braces are fastened with wood 

 screws. The rope-bridle is fastened 18 in. 

 from each end, to equalize the strain, as 

 shown in Fig. 3. The arrows denote the 

 line of strain. A spreader built with these 

 dimensions is sufficiently large for an aerial 

 300 ft. in length.— E. R. Thomas. 



Position of Wireless Waves Passing 

 Over Land 



WHEN radio waves travel along the 

 surface of the sea, or of any other 

 good conductor, their fronts stand up 

 nearly vertically. When they pass across 

 stretches of poorly-conducting earth, how- 

 ever, the tops tend to gain and the whole 

 wave-front tips forward in the direction of 

 motion. Resulting currents in the surface 

 of the earth cause resistance losses, and the 

 waves rapidly become weaker. This is 

 why it is more difficult to send wireless 

 signals over ground than over salt water. 



Cloudy Days Best for Wireless 

 Wave Signals 



MEASUREMENTS made at the Uni- 

 versity of North Dakota showed 

 that on the night following a cloudy day 

 signals were received much more clearly 

 than on nights following days of bright 

 sunlight. It appeared that the cloudiness 

 was most effective when it covered the 

 territory lying between the sending and 

 receiving stations. 



Improving the Tone of a Test Buzzer 

 Used on Wireless Detector 



THE tone of a buzzer used in finding a 

 sensitive spot on the crystal detector 

 can be made high-pitched by inserting a 

 piece of paper, folded four times, between 

 the contact spring and the bar next to the 

 magnet. Also insert a folded piece between 

 the cone of the first coil and the bar. 



Simple Construction of a 

 Rotary-Gap Disk 



IN the accompanying illustration is shown 

 a new type of rotary-gap disk which will 

 give unusually good results. It is very 

 easy to construct. First procure a piece of 

 3^-in. sheet fiber and cut out a disk 9 in. 

 in diameter. With a 4-in. radius draw a 

 circle on this and divide it off into 8 equal 



Holes in a fiber disk to allow the spark to 

 jump between the electrodes as it turns 



parts. Drill holes on these marks slightly 

 larger than the gap-electrodes and drill a 

 hole in the center for the shaft. Mount the 

 disk on a motor in the usual way with a set- 

 screw or clamp, and mount a stationary 

 gap as shown at A. Every time a hole is 

 passed, the gap is permitted to spark. 

 More holes can be added if desired, 

 depending on the speed of the motor. 



