Page:Popular Science Monthly Volume 88.djvu/644

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��Popular Science Monthly

��Experience and observation have shown that the "X" grade Hudson filament bulbs are the most satisfactory and economical.

Once the proper adjustments are dis- covered, the setting will be practically a constant for a stated wavelength, and it wuU likely be found that all the un- damped wave stations mentioned may be tuned to maximum strength of signals by slight changes in the capacity of con- denser II, perhaps tuning up condenser 3 for Sayville.

The continuous-wave stations are heard in clear, flute-like tones, the pitch of which may be varied in a wonderful and amusing manner by slight change of condenser 8 or ii, or both, or the prima- ry of the tuner, or inductances 13 and 14, or simply touching a metal part of the secondary circuit.

Particularly close tuning with arc stations is necessary, since usually two waves of practically equal energy but of slightly different length are emitted. One of them (the main wave) represents the dots and dashes and the other (the compensation w'ave) represents the breaks. Some difficulty may be ex- perienced in entirely suppressing the compensation wave, but the difference between the two may always be made sufficient for clear reading.

With this set the phenomenon of "stepped-up" voltage of the high-poten- tial battery may be taken advantage of to procure a further increase in volume of signals of spark stations. Arlington's spark signals may be brought in to a degree of loudness painful to the ear- drums by throwing in all of the tuner inductances, all of the secondary loading inductance and all of inductance 14, condenser 11 remaining at zero. South Wellfleet (WCC) can be made to "come in" like a grandfather bullfrog by similar manipulation, making due allow- ance for the shorter wavelength. The same is true, generally, of spark stations anywhere within reach, that work on 1000 meters wavelength or over. A far distant and relatively weak spark station may come in, not with the true note, but with a "whisper" effect. It is usually not practical to obtain perfect oscillation of the audion, resonance with and amplification of signals from stations

��using wavelengths of 600 meters and under, because of the circuit difficulties involved.

The experimenter who sets out to rig up a receiving set of this character is urged to avoid loose connections, im- perfect contact at switches, bunched and parallel connecting wires as much as pos- sible, and sloppy work generally, and to employ persevering patience in tuning the set to various stations until adept- ness is acquired. All switch handles should be of good insulating material, and no part of the operator's body should be allowed to come into contact with binding posts, switch levers or bare wires; the capacity of the body will prevent delicate adjustment. The in- ductances and condensers of the three circuits should be kept separate, each circuit a reasonable distance from the other, say a foot. Proper allowance must be made for the fact that signals that may be coming in ever so clearly may sometimes be almost or entirely suppressed by placing the hand or arm close to certain of the coils or condensers, or even close to the connecting wires. This is particularly true of undamped signals being received on a lower har- monic of the true wave.

Just a few words about winding the coils with the finer wire: Use a lathe, if available, or improvise one with a tool grinder, replacing the grinding wheel with a circular block that will just fit inside the tube; one tack will hold the tube to the block. A similar block, sup- ported and free to turn on a stud, will hold the other end of the tube. By lo- cating the spool of wire on a rod about 25 to 50 ft. away and starting the wind- ing carefully, the whole tube may be wound in a few minutes at high speed; the wire will "feed" itself, barring acci- dent. The taps may then be brought out by lifting the proper turns with the point of a knife blade, cutting the wire, unwinding a turn of each end, twisting them together and soldering the bare ends. The tubes may be w^ound with the coarser wire by hand and taps brought out as they are reached in winding. Any experimenter whose wire- less is equipped to receive undamped waves, should be able to obtain very in- teresting and valuable results.

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