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301 



Questions and Answers 



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WAVELENGTH. 



(7) W. P. R., Cresco, Iowa, asks: 



Q. i. My aerial consists of eight wires, 

 140 ft. long and spaced 3 ft. apart. I am 

 greatly bothered from static and am under 

 the impression that the number of wires does 

 not affect the strength of received signals. 

 If I should change my aerial to two wires 

 would I receive just as well and at the same 

 time cut the static down to one-fourth? 



A. i. The number of wires in the aerial 

 does have an effect on the strength of re- 

 ceived signals, but it is in no manner as 

 marked as in the case of transmitting. You 

 would not notice any great difference in the 

 strength of signals by cutting down your 

 aerial to two wires, but by doing so you 

 would gain little in the reduction of interfer- 

 ence from static. Better leave the arrange- 

 ment as it is. 



Q. 2. The wavelength of my aerial is about 

 300 meters. Could I reduce it to 200 meters? 

 If so, what value of capacity would it be 

 necessary to insert in series? 



A. 2. You could cut it down by inserting 

 a capacity of approximately 0.0002 m.f. This 

 is a heavy photographic plate 6 in. x 8 in. 

 coated to within an inch of the edges with 

 heavy tinfoil. 



Q. 3- What is the formula for calculating 

 the wavelength of a set when additional 

 capacity has been added in series? 



A. 3. If W is the wavelength in meters, L 

 the inductance in centimeters of the aerial 

 circuit, C the original capacity in micro- 

 farads of the aerial circuit, and K the added 

 capacity in microfarads, then 



Q. 4. What causes wireless signals to 

 fade? 



A. 4. The throwing out of adjustment of 

 the detector and loose connections are the 

 most prolific causes of fading signals. Other 

 than this, there are the atmospheric conditions 

 which cause both fading and swinging. 



REWINDING MAGNETO MACHINE. 



(8) B. H., Ithaca, N. Y., asks: 



Q. i. How can a low-tension Kellogg mag- 

 neto telephone bell ringer be changed into 

 high-tension motor suitable for operation on 

 battery currents? 



A. i. Undoubtedly you have just ex- 

 changed the use of the high and low-tension 

 statements, for you mean how to turn the 

 relatively high tension 75 volts alternating- 

 current generator into a low-tension 6 volts 

 direct-current motor. Dependent upon the 

 room available at the connection end of the 

 armature and your facility with tools, you 

 will have satisfactory results, or otherwise, 

 with the attempt. After removing present 

 wire, draw out the insulated pin and the 

 insulation itself you will need the full size 

 of the hole for the two commutator wires. 

 Insulate the iron core with "Empire" cloth, 

 taking especial pains to cover the sharp edges 

 that are difficult to keep away from the wire. 

 Perhaps No. 23 would be a good size to use, 

 and, instead of beginning at one end of the 

 wire, estimate about what length will be re- 

 quired, make a loop, and begin at the middle, 

 winding a dozen or twenty turns first with one 

 end, then with the other, the result being that 

 both terminals are outside ones. To these 

 ends solder "fixture" wire, or such other 

 flexible sort as can be led through the hole 

 in the shaft. A disc rather than a cylindrical 

 commutator can be made by use of a fibre 

 washer, say % in. or more in thickness, on 

 which is fastened by at least four small screws 

 a brass or copper washer about i in. in out- 

 side diameter, with large enough hole to clear 

 the shaft. A diametrical saw-cut can be then 

 made, separating the washer into two semi- 

 circles, and one of the two wires pinched 

 under each. Let the two copper brushes stand 

 up vertically from the wooden base, bent at 

 their contact with the commutator so as to 

 permit rotation in either direction. With the 

 field magnets pulling the "H" armature into 

 its resting position the tips of the brushes 

 should be bridging across the saw-cut. 



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