What Radio Readers Want to Know 



Range of Station 



S. D., Glendale, Cal., inquires : 



Q. 1. With a four-wire aerial, 100 feet in 

 length by 55 feet in height at one end and 

 70 feet at the other, connected with a "1500- 

 meter" tuning coil, galena detector, 1000-ohm 

 receivers, 43-plate variable condenser and a 

 fixed condenser, how far should I be able to 

 receive ? 



A, 1. The daylight receiving range of this 

 apparatus is perhaps 250 miles, while the night 

 range may be 1000 miles, depending largely 

 upon the power of the transmitting station 

 from which it is desired to receive. 



Q. 2. With the foregoing aerial, -^/i K. 

 W. transformer connected to the proper con- 

 denser and oscillation transformer, how far 

 can I transmit and approximately what will be 

 the wavelength emitted? 



A. 2. The natural wavelength of the an- 

 tenna system is about 300 meters, and ra- 

 diated, it win be above that value by an 

 amount depending on the number of turns and 

 the general over-all dimensions of tlie second- 

 ary winding. If your station is located so 

 that the Government Authorities will allow it 

 to be operated at a wavelength of 300 meters, 

 the daylight range will be approximately 50 

 miles. At a wavelength of 200 meters its 

 probable range will be from 20 to 30 miles. 



Condenser for Transmitter 



LeR. D., Milwaukee, Wis., inquires : 



Q. 1. How many plates of glass, 8 inches 

 by 10 inches covered with tinfoil 6 inches by 

 8 inches, are required to make a suitable con- 

 denser or a % K. W. Thordarson trans- 

 former? 



A. 1. Assuming that this condenser is to 

 be operated at a wavelength of 200 meters, its 

 maximum capacity in any case cannot exceed 

 0.01 Mfds. With the dimensions given, the 

 capacity of each plate is approximately 0.0000 

 Mfds. For a value of 0.01 Mfds. approxi- 

 mately 16 plates should be connected in par- 

 allel. If the potential of the transformer is 

 20,000 volts, the condenser should be split into 

 two banks. You then require 32 plates con- 

 nected in parallel in each bank and two such 

 banks connected in series. 



Q. 2. Please give the construction of a 

 0.5 Microfarad condenser. 



A. 2. We infer that this condenser is to 

 be somewhat similar in construction to the 

 type used in telephone work and operated at 

 low potentials. If so, two strips of foil, 6 

 inches in width by about 90 feet in length, are 

 separated by a similar thin strip of paraffin 



paper. A second sheet of paraffin paper is 

 then placed over one of the tinfoil strips and 

 the entire unit wound up in circular form. 

 The connections from each strip may be 

 brought out to a binding post. 



Q. 3. How many electrodes should be em- 

 ployed in connection with a rotary spark-gap 

 having a disk 6 inches in diameter? The mo- 

 tor has a no-load speed of 6000 R. P. M. 

 This gap is to be used with a % K. W. trans- 

 mitting set. 



A. 3. With the transformer operated from 

 a 60-cycle source of current supply, it is not 

 advisable to produce more than 300 to 400 

 spark discharges a second. Assuming the 

 load speed of the motor to be about 4000 R. 

 P. M., it is recommended that the disk be 

 fitted with 6 discharge electrodes equally 

 spaced about the circumference. Excessive 

 speeds are undesirable and unnecessary. The 

 average commercial, non-synchronous, rotary 

 spark discharger operates at a speed of 2400 

 R. P. M. and has 10 discharge electrodes 

 mounted on the disk. 



Q. 4. What are the names of the cities 

 corresponding to the abbreviations sent out 

 from Arlington in the weather forecasts, such 

 as M, C, U? 



A. 4. These abbreviations refer to impor- 

 tant weather observation points. An interpre- 

 tation follows : T, Nantucket ; S, Sidney ; A, 

 Atlantic City ; H, Hatteras ; C, Charleston ; K, 

 Key West; P, Pensacola; B, Bermuda. For 

 the Great Lakes the designations are as fol- 

 lows : DU, Duluth ; M, Marquette ; U, Saulte 

 St. Marie ; G, Green Bay ; CH, Chicago ; L, 

 Alpina ; D, Detroit ; V, Cleveland ; F, Buffalo. 



Inductively Coupled Tuner 



W. M. K., Windsor, Ontario, writes : 

 Q. 1. I have an inductively-coupled re- 

 ceiving tuner with a primary winding iVz 

 inches in diameter by 6 inches in length. It 

 is covered for 5 inches with No. 18 enamel 

 wire. The secondary is 6 inches in length by 

 3V2 inches in diameter covered for 5 inches 

 with No. 24 single cotton wire. Kindly ad- 

 vise the range of wavelength. 



A. 1. The range of wavelength to which 

 this apparatus is responsive depends upon the 

 size of the variable condenser employed in 

 shunt to the secondary winding, but with one 

 of very small capacity it .should be adjustable 

 to about 2500 meters. The present winding 

 does not represent the best design for an ef- 

 ficient tuner, since No. 24 wire is preferred 

 for the primary winding and No. 30 or 32 for 

 the secondary winding. 



472 



