788 



Popular Science Monthly 



the closed circuit across the secondary 

 terminals of the spark coil. The advantage 

 of this arrangement is in line with the idea 

 that a transmitter operates best at a wave- 

 length I y% times the natural period of the 

 aerial. Many amateurs extend their an- 

 tennas to greater lengths, use only one or 

 two turns in the secondary of the oscillation- 

 transformer, and then wonder why their 



Transmitting condenser constructed of glass 

 plates coated on both sides with tinfoil 



range is not all it should be. It may be 

 interesting to note that the author uses a 

 4-wire inverted L aerial 55 ft. high and 

 only 35 ft. long on the flat top portion. 



The aerial must be very carefully 

 insulated. Use ball insulators on each 

 wire in the flat top portion, electrose strain 

 insulators on the spreader bridles, and 

 porcelain cleats on the sway guys. 



The lead-in deserves as much attention as 

 the aerial proper. Bunch the wires im- 

 mediately beneath the aerial and connect 

 with a No. 4 copper wire, insulated from the 

 rod by large porcelain knobs. Unless already 

 insulated, it is best to wrap the wire with 

 electric tape where it comes into contact 

 with the knobs. The wire should be 

 passed through a porcelain tube when it 

 enters the operating room. All joints must 

 be securely soldered. The commonest 

 cause of weak, swaying, fading signals is a 

 loose, corroded connection in the aerial or 

 lead-in. 



As the slate base of the ordinary light- 

 ning switch is absolutely unfitted to prevent 

 leakage into the ground of the high voltage 

 currents, it is important that defective 

 insulation at this point be remedied by 

 raising the base on fiber strips. 



The saying that "a good ground is as 



essential as a good aerial" is true, for an 

 indifferent ground connection severely crip- 

 ples any station. One of the reasons why 

 ship stations can transmit so much farther 

 with a given amount of power than many 

 land stations is that it is possible on ship- 

 board to secure a perfect ground. The. 

 range of the writer's station was increased 

 thirty per cent, by running extra ground 

 wires to the watertank up in the attic, to 

 the gas-pipe in two places, and to the 

 heating system as well. This was a great 

 surprise, as I had been using a connection to 

 the water pipe on the street side of the 

 meter, that I considered excellent. Sta- 

 tions situated on hilltops where there is 

 little moisture in the ground due to down- 

 hill drainage must take special pains to 

 secure an efficient ground. 



Never forego an opportunity to reduce 

 the resistance of any of the connecting 

 wires, the lead-in, or ground connection. 

 The greater their conductivity, the greater 

 the radiation, and an increase in the sharp- 

 ness and purity of the emitted wave will be 

 noticed. 



Now for the set itself. We shall first 

 consider the construction of the trans- 

 mitting condenser. With hot water re- 

 move the emulsion from five 3^ in. by 4^ 

 in. photographic plates, and coat three of 

 them on both sides with tinfoil, leaving a 



The helix has twelve turns of copper ribbon 

 placed in notches sawed in cross sticks 



margin of ^ in. around the edges. As an 

 adhesive use orange shellac, not white 

 shellac. Next paint the two remaining 

 plates with the liquid, and when it has 

 become sufficiently dry to be very sticky, 

 pile the five plates together as shown in Fig. 



