Page:Popular Science Monthly Volume 91.djvu/804

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��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.

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