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Page:Popular Science Monthly Volume 89.djvu/803

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How to Become a Wireless Operator

III. — The Construction of a One-Mile Receiver

By T. M. Lewis

��IT IS most important for a student of wireless telegraphy to learn all about the operation of the various forms of receiving apparatus. The best way to become familiar with the instruments is to build and operate them. The simple buzzer-sender and microphone receiver which were described in the first article of this series served to illustrate the principles which are followed in all wireless apparatus, but were of such small signaling range that they could not demonstrate fully the details of modern instruments. The one-mile transmitter shown last month, however, when used in connection with the receiver now to be explained, is of suf- ficient size to ap- proach the c o n - ditions of opera- tion existing i n commercial radio stations. By studying its action carefully the ex- perimenter can learn much which will be of inestim- able value to him in his later prac- tice of wireless telegraph operation.

The student should remember that the use of a transmitter as powerful as that described in the second article, even though it is a very small one when compared to some of the great commer- cial, plants, may cause interference at nearby receiving stations. He should therefore be very careful to observe all of the regulations and courtesies as to transmitting, and should send only when he actually has a message which he wishes delivered to his communicating station. One of the first habits which a successful wireless operator should cul- tivate is to refrain from sending except when it is absolutely necessary. Testing of the spark-gap should be done with

���Fig. 1. A cross-sectional view of a crystal detector stand that is easily constructed

��the aerial disconnected, and code prac- tice should be carried on with buzzers. There is never any objection to the amateur who sends actual messages with a wavelength of less than 200 meters (the range assigned to amateur stations by the Government) but the man who keeps tapping his key and sending out interfering waves which hold up legiti- mate messages soon becomes extremely unpopular with both the serious amateurs and the professional operators.

The Detector

Probably the most important element of any receiving outfit is the detector, which is an instru- ment for convert- ing the received high- frequency current into pulsa- tionswhich operate the telephones. The microphone which was d e - scribed in the first article is a wave- detector of a very easily constructed tj'pe, and is always worth remember- ing for use in an emergency. It is very delicate, but is not so reliable nor so sensitive as the crystal detector which is illustrated in Fig. i. A well made crystal detector is about the best instru- ment for all around use that can be had. Apparatus of this type is installed at by far the greatest number of commer- cial radio stations, and every operator should be familiar with its adjustment and use.

A side view of a detector-stand, which has been found very satisfactory- in practical work, is shown in Fig. i. The construction should be clear from the drawings, and a brief description. Di- mensions are not given, since it is usually most convenient to modify them slightly

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