Popular Science Munthlt/ 



959 



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. 



F 



AERIAL 

 SHAIL AERIAL CUT OUT SW, 



10 INSTRUMENT ^^ Z-ZO AMP FUSES 

 WALL W<J 



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. 



