Page:Popular Science Monthly Volume 89.djvu/466

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��Popular Science Monthly

��distance of five hundred or a thousand feet; with larger aerials even greater distances can be covered. Begin in a small way, however, and make your progress a step at a time.

If you are near a commercial or Naval wireless station you will be able to receive signals from it by using the apparatus of Fig. 4; belter arrange- ments which will operate over longer distances will be explained in later articles, however. The microphonic detector of Fig. 3 is quite useful when connected to a commercial wireless tuner, and knowing how easily it may be built from material commonly at hand may be of value even to _ the commercial wireless operator, in times of emergency.

You will hnd it important to become a good telegraph operator if you propose to continue wireless experimenting. There are a number of pamphlets and books published which explain methods of learning 4:he Morse code; Chapter IV of "The Book of Wireless," by A. Fred- erick Collins, gives a good method to follow. Cards showing the International Morse Code in full may be obtained from the Radio Inspectors' offices at Boston, New York, Baltimore, Savan- nah, New Orleans, San Francisco, Cleve- land and Chicago. It is only by con- stant practice that you can become proficient.

( To be continued )

A Rotary Adjustment for Coupling

ASIMPLE method of building a rotary adjustment for coupling of receivers is shown in the drawing, where A is the primary coil, B the .secondary coil, and C indicates the slide rotls for the secondary. At D is shown a small square brass rack which meshes with a

��small pinion about ]/2 in. in diameter at /•". The pinion is carried on shaft J, which is su[)ported in small angles made of 1/16 in. sheet brass, as shown at H. A hard rubber or fiber knob is shown at G. The rack D may also be attached to the secondary coil with a small angle of i/i6-in. brass. A hole should be bored through the end-piece / to permit D to slide through. The brass rack and pinion may be purchased from an\' dealers in model supplies. The arrange- ment will be found well worth the trouble of making, since a very fine adjust- ment of coupling may be invariably obtained. — C. H. R.wschenberg.

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��51* Hm <//iix*, Sijffiffnon

���A Curious Form of Dustproof Detector Cup

T is well known that detectors of the mineral type rapidly depreciate in sensitiveness when the minerals become

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��covered with dust, endeavor to nuisance by detector with a

��A great many overcome this co\cring llie jeweler's glass

���ArranRcmcnt of Coils in Rotary Adjust- ment for the Coupling Receivers

��COUNTS fIBORL IN WOOD

��Scheme to Protect Detectors of the Min- eral Type from Dust

bell or by other means. A new scheme is shown in the drawing. The mineral cups are placed on a brass bar or disk. .1, supported by an adjustable threaded rod B.

A fine "cat-whisker" wire contact point of the usual lyjie ma\- be placeil on a brass spring C, which has its ten- sion adjustable by means of a threailed rod anil knob D. At first this may seem a little inconvenient, but it really is just as easy to adjust as if the min- eral cups were facing uinvard, as in most detectors. This is because the sensiti\c si)ots DU the miner, d arc loimd b\- feel- ing around with "cat-whisker" contact.

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