Page:Popular Science Monthly Volume 89.djvu/973

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Popular Science Munthlt/


��Lightning Protection, Receiving Coil and Condenser

L. P., Miami, Fla., writes:

Q. 1. Referring to the attached diagram, would the apparatus and the connections shown therein be sufficient protection from hghtning if located on the outsifle of a wooden house?

A. 1. The National Inspection Code requires that the antenna be connected to earth through a lOO-amiK-re single-blade double-throw switch, and that the earth connection from this switch be made up of at least No. 4 D.B.R.C. wire. Fuses are of no value for protecting the receiving apparatus because even if they should blow the voltage of the next lightning discharge may be sufficient to jump the gap left by the burned fuse. Mount the ux)-ampere switch on the outside of the house in an asbestos-lined box and during severe lightning storms totally disconnect the receiving apparatus from the aerial wires.




��Q. 2. In the winding of tuning coils with bare wire, what prevents adjacent turns from actual contact? Is the tube grooved?

A. 2. Yes, it is threaded on a screw-cutting lathe. A fine thread is of course required. Some- times a cord is wound between the turns of bare wire.

Q. 3. Please give the dimensions for a small receiving condenser?

A. 3. If reference is made to the stopping condenser it may be made up of 20 sheets of tin- foil 2 in. x3 in. alternated and separated with thin paraffined paper. The entire unit after assembly should be compressed between two strips of wood or hard rubber. See the article by T. M. Lewis in the November, 1916, issue.

Call Book; One Kilowatt Transformer

F. McM., Fairchance, Pa., inquires:

Q. 1. Where may I secure a copy of the new government call book?

A. 1. Send 1 5 cents to the Government Print- ing Office, Washington, D. C. A new issue was off the press in July.

Q. 2. Please give the necessary dimensions for a I K.W. closed core transformer, using No. 20 wire on the secondary with the understanding that the secondary winding is to be made in two sections.

��A. 2. No. 20 wire is too large for the second- ary winding of a transformer of this capacity. The complete core for a I K.W. transformer when assembled should be 11 in. x 10 in. outsidfi measurements, and the legs 2 in. square. The core is of course made up of a number of pieces of sheet-iron cut to the required length. The primary winding should comprise six layers of No. 12 D.C.C. wire. Approximately seven pounds are required. The secondary winding requires 18 lbs. of No. 32 enameled wire which may be split up into ten sections. It is intended that the primary and secondary windings be mounted on the opposite ends of the core. The primary winding may be insulated from the core by means of eight or ten thicknesses of Empire cloth. The secondary winding may be insulated from the core by means of Empire cloth, enough layers being added to make a separation of at least 3/8 in.

Q. 3. Which of the vacuum-valve bulbs do you consider the most efficient, first as a detector, second as an oscillator; namely, the thermotron tubular audion, oscilaudion, electron relay, and audiotron?

A. 3. All of the bulbs which you mention work on practically the same principle and are more or less identical in operation. We have no preference and know that good results have been obtained with all of them. As an ordinary detector for the reception of signals from damped stations the ordinary audion bulb is preferred, provided it possesses a certain amount of gas, but as an oscillator for the reception of signals by the "beat" method, the highly exhausted bulbs such as those you mention are to be pre- ferred.

Q. 4. What do you consider the best way to use these bulbs, and if possible, give a diagram of connection, first as a detector, second as an amplifier with silicon, third as an amplifier with the Type "A" crystaloid detector.

A. 4. The question is rather comprehensive and would require pages for a complete explana- tion. Circuits of this type are fully covered in the book "How to Conduct a Radio Club." .-V copy of this book may be purchased from the Book Department of this magazine at cost of 50 cents. Several types of oscillating audion cir- cuits are described.

Q. 5. Can you give me the wavelength and the hours of operation of high f>ower stations within my range other than Arlington and Sayville?

A. 5. With a long distance receiving set re- sponsive to wavelength up to 8,000 meters, >-ou should be able to hear the Naval Station at Lake Bluff, 111., and another government station located at Darien, C. '/... Isthmus of Panama. The hours of operation are irregular but they may be heard at intervals throughout the day.

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