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Page:Popular Science Monthly Volume 89.djvu/964

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950

��Popular Science Muiilldy

��transmitter. The simplest way to do this is to connect a small single-pole switch (either a knife-switch or a lever-switch of almost any sort will do) directly across the terminals of the detector. In the wiring diagram of the complete station, Fig. 2, the tlctector-protecting switch is marked S; the wires leading from it to the Ijinding posts of the detector should l)e kept as short as possible; otherwise they may pick up enough current from the sending-spark to "knock out" or destroy the sensiti\e adjustment of the crystal-detector. Wiien receiving, the protecting-switch 5 must be open, so that the detector can operate to rectify the currents [jroduccfl in it by the incoming waves. When sending, the switch must be closed. In this position the heavy induced currents are shunted past the detector and the adjustment is not dis- turbed by them.

Connecting the Complete Set

In addition to the parts of the receiving station fully described in last month's article, the various elements of the trans- mitter illustrated and discussed in October will be needed for a complete sending and receiving station. In fact, a complete set of parts is necessary for each terminal of the proposed wireless "line." The following must, therefore, be at each plant:

Station:

1 Antenna and support See September and October articles. I Loading Coil " October article.

I Ground Connection " September " I ChanRC-Over Switch " above. Necessary wire for connections.

Sender:

I Set of dry or storage- cells See October article. I Sending Key " I Induction Coil " " " I Spark-Gap " " "

Receiver:

I Crystal- Detector See above.

I Stopping-Condenser " "

1 Pair of Telephones " "

I Test-Buzzer " September article.

I Strap-Key " "

I Dry Cell

I Uetector-Protecting

Switch " above.

The above-named elements of the com- plete station must be carefully connected together as shown in Fig. 2. It is a good plan to use No. i6 or No. i8 lamp-cord for the wiring of a set such as this. The twisted pair should be separated and

��smoothed out, and the single conductors used independently.

It is necessary to keep the transmitting

���TLrTf-Js^^t

��5;.. GROUND

��FIG 2

��SENDING KEY

The wiring diagram of a complete station showing the location of wireless apparatus

apparatus well away from the receiving instruments. The loading coil, for example, should not be nearer than two feet to the detector, telephones and stopping-conden- ser. As explained in the second article of this series, the lead-wire from the loading coil out to the aerial must be well insulated if good work is to be done. It is very important that the change-over switch be well insulated, also, for three of its contacts arc subjected to the full sparking potential of the transmitter (see the diagram of Fig. 2).

The best plan for beginning work is to have the two antennas, one at each station, as nearly alike as possible. If their form and height cannot be made identical, they shotild at any rate have exactly the same length of circuit. That is to say, there should be the same number of feet measured from the ground connection tij) through the spark-gap (but not through the loading coil) to till' distant insulated end of the antenn.i, within a few per cent. In this case, i. e., with the lengths practically identical, the loading coils at the two stations can be put entirely in circuit, and the app.irattis will be approximately tuned for the interchange of messages.

If one of the aeri.ils is longer than the other, less of the loading coil should be used at that station than at the other. Tlu' I'xact point to clip on to the wire of the loading coil can be determined only by exi)erinunt. By tr>ing every turn, it will be found that some one position is

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