614 



Popular Science Monthly 



location and skill, from the Navy station 

 at Darien, which is about 1800 miles 

 from Washington. He may also receive 

 signals from spark stations many hun- 

 dreds of miles farther away than before, 

 and "bring in" the stations which he has 

 been hearing from two to ten times as 

 loudly as before. 



The accompany- 

 ing illustrations 

 portray an arrange- 

 ment of three tun- 

 ed circuits, the 

 open (antenna) cir- 

 cuit, the secondary 

 circuit, and the au- 

 dion wing (high po- 

 tential) circuit. The various condensers 

 and inductances shown are the usual 

 tuning devices. 



The antenna in use with the set here 

 described consists of two stranded copper 

 wires 250' long, spread 4' apart on 

 bamboo spreaders, raised 30' above level 

 ground, located up in the mountains of 

 northeastern Pennsylvania. The anten- 

 na, with the aerial tuning inductance, 

 primar}- of inductively-coupled tuner and 

 the condenser shunted around the aerial 

 tuning inductance and the primary 

 winding, permits of tuning to resonance 

 with from 1000 to 8000 meters wave- 

 length. Tuning to shorter wavelengths 

 may be done by cutting in the condenser 

 shown in the ground wire. With this 

 set it has been easily possible to read 

 signals from the Navy station at Darien, 

 Panama, day or night, ever since the 

 station was opened. 



The constants of the aerial, inductan- 

 ces and condensers may be varied, of 

 course, and those in use or on hand in 

 •most advanced amateur stations may, 

 perhaps, serve the purpose; but in the 

 aggregate a fine degree of resonance 

 must be procured. All inductances (save 

 those of the tuner) are in oak boxes; the 

 tubes are fastened to the lids by brackets, 

 with the switches on top of the lids. 

 This arrangement permits the entire 

 unit to be lifted out of its box without 

 disturbing connections, if desired. Tap 

 leads inside are covered with soft rubber 

 tubing. Coil boxes may be placed on 

 end to save space. 



The tuner is of the familiar inductively- 

 coupled navy type; the inductances in 



How the inductance coils are made 



both tuner circuits are variable by 

 switches only, 16 ten-turn and 18 one- 

 turn in the primary, and 12, equally 

 spaced, in the secondary. Inductance i is 

 made of a paper mailing tube, 3" outside 

 diameter, 18" long, and wound closely 

 over 16" of its length with No. 25 DCC 

 wire. Including the 

 ends of the wind- 

 ing, ten taps, equal- 

 ly spaced, are led 

 to a ten-point 

 switch. Inductance 

 6, in the secondary 

 circuit, is made of a 

 paper mailing tube, 

 3" by 18", wound 

 closely for 16" with No. 36 DCC wire; 

 and 10 equally spaced taps are led to a 

 ten-point switch. Inductance 13 is iden- 

 tical with inductance 6. Inductance 14 

 is of the same dimensions but it is wound 

 with No. 25 wire for use when tuning to 

 shorter wavelengths, and to permit fine 

 variations in conjunction with inductance 

 13 when tuning to long waves. All con- 

 densers (except that around the high- 

 potential battery) are of the familiar 

 segmental variable type, with range of 

 capacity from 0.0008 to o.ooi mfd. 

 Condenser 3 is filled with castor oil, 

 giving it a maximum capacity of approxi- 

 mately 0.004 mfd. It is used to boost 

 the wavelength of the antenna circuit. 



Rheostats 9 and 10 are employed to 

 regulate the filament voltage. One is 

 the ordinary rheostat that is a part of 

 every audion detector. It has a total 

 resistance of about 10 ohms. The other 

 has a total resistance of only i}/2 ohms 

 in 10" of length. This second rheostat 

 is not absolutely essential, and may be 

 omitted, but it has been found to be very 

 convenient to have such a rheostat for 

 closely regulating the lighting voltage, 

 whether storage or dry cells are used. 

 The condenser 15 shunted across the high 

 potential battery is of the ordinary tele- 

 phone type, of from i to 2 mfds. capacit^^ 

 Condenser 18 may be either a true 

 variable, or a variable-fixed condenser 

 susceptible of several changes of capacity. 

 The function of these condensers is to 

 provide paths of low impedance, for the 

 high-frequency currents, around the high- 

 potential battery and the telephones. It 

 is considered good practice to have a 



