Popular Science Monthly 



633 



altogether. With both switchblades at the 

 left, in positions W and F, the condenser 

 is in series, as shown in Fig. 5. When both 

 switchblades are thrown to the right, in 

 positions X and Z, the condenser is in shunt 

 to the primary coil, as in Fig. 4. When 

 the upper switchblade is at the right and 

 the lower at the left, i.e., in positions X 

 and Y, the variable condenser is cut out 

 and the circuits are connected as shown in 

 Fig. 2. This same switching arrangement 

 may also be used with the autotransformer 

 arrangement of Fig. i . Practically the same 

 results will be secured, except that the pri- 

 mary turns are changed whenever the switch 

 C (Fig. i) is moved to vary the coupling. 



Experienced radio operators, as well as 

 beginners, will find it worth while to study 

 the principles explained in this article. 

 They are the basis of successful operation 

 of the coupled receiving sets. 

 {The end) 



Power Measurement Method Without 

 a Watt-Meter 



MANY amateur electricians would like 

 to know the power consumption of 

 devices they construct, but do not have 

 access to a watt-meter. The watts con- 

 sumed may be found as follows: Turn ofif 

 all lights in the house except one of known 

 power consumption, and count the number 

 of seconds required for the watt-hour 

 meter's disk to make one revolution. Then 

 turn out all lights, connect into the circuit 

 the device whose power consumption you 

 desire to know, and again count the number 

 of seconds for the meter disk to make one 

 revolution. 



To find the power consumed by the 

 device, multiply the watts of the lamp by 

 the number of seconds required for a revolu- 

 tion of the meter disk when connected and 

 divide by the number of seconds required 

 for a disk revolution with the device itself 

 connected. For example, one meter re- 

 quired 30 seconds for one disk revolution 

 with a 25-watt lamp connected, and 60 

 seconds with a small transformer furnishing 

 current to a small motor connected with it. 

 The power consumption of the transformer 

 and motor was thus 25 X 30 4- 60 = 12.5 

 watts. If the disk runs so fast that it is diffi- 

 cult to time it for one revolution, the time 

 for a greater number of revolutions should 

 be taken, the number being the same with 

 the device tested as with the lamp. 



An Easily Constructed Detector-Stand 

 for Wireless Instruments 



A DETECTOR-STAND can be easily 

 made from a few simple materials. 

 Procure a piece of brass 1/16 in. thick, and 

 cut it into the shape shown at A. The 

 openings may be made by drilling holes and 



A detector-stand which can be easily made 

 by the amateur from a few simple materials 



filing the edges. Bend the brass on the 

 dotted lines so that a U-shaped piece is 

 formed with the slots parallel. 



Obtain a brass or copper ball l^ in. in 

 diameter, and drill a hole through it to 

 admit a brass rod i^ in. long. Thread one 

 end of the rod to fit the insulating knob. 

 Solder the ball and a piece of fine brass 

 wire on to the rod, as shown at C. The 

 point of a gold scarf-pin may be soldered 

 on to the end of the wire to serve as a "cat- 

 whisker." It is easily adjusted. 



The standard B is heavy brass, bent on 

 the dotted lines. The cup, with the crystal, 

 is fastened to it with a screw as shown. The 

 inverted position of the crystal prevents 

 dust from settling on it and maintains its 

 sensitiveness. The base may be made of 



&£ti^^ 



6o/(f pant 



Construction diagram of the home-made 

 detector-stand showing dimensions 



hard rubber or any hard wood. Be sure 

 that the uprights of the piece A are just 

 tight enough to hold the ball in place. The 

 knob can be moved backward or forward, 

 or in any direction desired to secure the 

 best crystal setting. — G. F. Exner. 



