960 



Popular Science Monthly 



An excellent oil-tight case can be made at 

 small cost from an aluminum cup about 

 ^^2 ill- i" diameter. Glass cases can be 

 made from large paste pots, oil-cup glasses, 

 etc., or if desired complete composition 

 cases can be purchased ready made. When 

 mounted in any cabinet set the appearance 

 of the instruments in question can be made 

 to equal that of any condensers made. 

 The maximum capacity of the condensers 

 described is approximately .008 microfarad. 



If these instructions are carefully fol- 

 lowed, the results will be very gratifying. 

 There are many minor points brought out 

 in the description which represent several 

 months* experimentation on the part of the 

 author. Although slight variations of con- 

 struction may appear feasible, it should be 

 borne in mind that such deviations should 

 be attempted only with the idea of experi- 

 mentation. In order to do anything right 

 the first time, it must be done according to 

 rule. Experimentation often means de- 

 struction instead of construction. 



The total cost for materials used in 

 making two condensers by the above 

 method should not exceed $1.50 exclusive of 

 cases. The time required may vary from 

 6 to 20 or more hours. Tests should be 

 made for short circuits with head-phones 

 and a battery. 



An Improved Method of Aerial 

 Construction 



THE construction of an aerial is greatly 

 simplified if the wires are cut equal to 

 the length of the aerial proper, plus the 

 length of the lead-in, and connected as in 



AERIAL 



the drawing. It is 

 understood that this 

 represents but one wire 

 of the aerial. As many 

 may be used as required. 

 The chief advantages 

 of this form of con- 

 struction are that it 

 requires no soldered 

 joints, since the wire is 

 in one piece from the lightning switch to the 

 top of the aerial ; that it has no sharp corners 

 to start brush discharges, and that the 

 lead-in has very nearly the same current 

 carrying capacity as the aerial, since it is 

 made up of exactly the same number of 

 ,wires. — Edward L. Norton. 



LEAD-W 



Simplified connec- 

 tion for an aerial 

 wire and the lead-in 



Some Useful Hints for the 

 Radio Operator 



IF your tuner is wound with bare wire on a 

 threaded core, and the wire has v/orked 

 loose, put it in the refrigerator over night 

 so that the chill will contract the tube. 

 Immediately upon removing it, work the 

 wire tight with the hands and fasten. As 

 the tube warms to the temperature of the 

 atmosphere it will expand, thus drawing the 

 wire tighter than could be done with a 

 machine. 



Wipe off the tuner switch contacts with 

 a piece of silk and rub the blade back and 

 forth over some 0000 French emery paper 

 about once a week. This will keep the 

 blade from wearing rough, and the switches 

 will always work without scraping. 



Silk is one of the best materials for keep- 

 ing the surfaces of rubber and nickel parts 

 bright. 



Rub old and discolored hard rubber 

 panels briskly with some cheesecloth sat- 

 urated in household ammonia, and finish 

 with a piece of silk dipped in crude oil, to 

 restore to the surfaces their former black 

 color and polish. 



Use a battery-switch instead of a button 

 on your buzzer test circuit. This will 

 enable you to use both hands in adjusting 

 the detector. 



If your cabinets are all finished with wax 

 or oil instead of varnish, they will not show 

 dust, finger marks, smears, etc. Dull 

 nickel plate holds the same advantage over 

 the polished kind. 



A relay can be employed to advantage by 

 connecting the magnets with an arm on the 

 antenna switch and using the contacts for 

 short circuiting the detector while sending. 

 With the relay in circuit, throwing over the 

 aerial switch may perform five operations, 

 namely: It may disconnect the receiving 

 set from the aerial, short circuit the detec- 

 tor, connect aerial to oscillation transform- 

 er, connect power to transformer primary, 

 and start the rotary gap motor. 



A pair of amber, smoked or blue glasses 

 will protect the operator's eyes from the 

 strain and burning sometimes caused by the 

 spark. 



If you desire to get efficiency on a 200- 

 meter wave, which means that the closed 

 circuit connections must be as short as 

 possible, mount your condenser and trans- 

 former together in the same case, and 

 arrange your gap on top of them. Fill the 

 case with oil. — Edwin L. Powell. 



