What Radio Readers Want to Know 



Receiving Tuner; Sending Condenser 



L, J. T., St. Louis, Mo., inquires: 



Q. I. Some confusion exists in my mind 

 regarding the designs for receiving tuners. Take 

 for example the following: For a receiving tuner 

 to be adjustable to wavelengths from 175 to 

 4,000 meters, is it preferable to construct two 

 separate tuners or may two small-sized tuners be 

 joined together (in the primary and secondary 

 windings) to receive the longer wavelengths? 

 Also, what is the most desirable size for the 

 cylinder and the size of the wire in the primary 

 and secondary? Is single cotton-covered wire 

 better than enamel wire? In addition, approxi- 

 mately how many taps are required on the 

 secondary' winding? 



A. I. A receiving tuner of this range is 

 practical provided the precaution is taken to fit 

 it with dead-end eliminating switches. If the 

 dead-end losses are to be wholly eliminated, you 

 are advised to construct two separate tuners. 

 Assuming that the smaller tuner is to be used for 

 amateur work It may have the following dimen- 

 sions: The primary winding Is 3 J Ins. In diame- 

 ter by 2 Ins. in length covered with from 80 to 85 

 turns of Xo. 28 D.S.C. wire. The secondary 

 winding Is 3 Ins. in diameter by 2 Ins. In length 

 covered with Xo. 30 D.S.C. wire. The secondary 

 winding Is equally divided between the taps of a 

 three-point switch, while the primary winding 

 may be fitted with a slider. Connected to an 

 aerial of the dimensions found at the usual 

 amateur station, the following described receiving 

 tuner will permit adjustments In both the 

 antenna and detector circuits to a wavelength of 

 4,000 meters. The primary winding Is 4 ins. 

 outside diameter by 7 Ins. In length and is wound 

 closely with Xo. 24 S.S.C. wire. The secondary 

 winding is 3^ Ins. In diameter by 6 ins. in length 

 wound closely with Xo. 30 S.S.C. wire. The 

 turns of the latter winding should be equally 

 divided between the points of a ten-point switch. 

 The primary windings may be fitted with a slider 

 or preferably two lo-point switches, one of which 

 takes in a single turn at a time and the second 

 one connects in a number of turns In groups. 



The secondary winding must be shunted by a 

 condenser of 'small capacity; one of .0005 micro- 

 farad capacity will permit the reception of wave- 

 lengths In the vicinity of 4,000 meters. 



If you are familiar with the construction of 

 dead-end switches the windings of the long wave- 

 length tuner may In this manner be broken up 

 into groups and a small portion used for the 

 reception of amateur signals, though the efficiency 

 will probably not be so high as when two different 

 tuners are used. 



Q. 2. Please give the dimensions for a con- 

 denser to be connected to a i-k.w. transformer 

 regardless of the 200-meter wave. 



A. 2. The proper capacity of the condenser 

 depends upon the secondary voltage of the trans- 

 former and the frequency in cycles per second. 

 Lacking this data we can not advise. If the 

 potential of the transformer is 20,000 volts at a 

 frequency of 60 cycles. It Is customary to fit it 

 with a condenser having a capacity varying from 

 0.012 mfd. to 0.018 mfd. A single plate of glass 

 -J In. in thickness with other dimensions 14 ins. by 

 14 ins. covered with foil 12 ins. by 12 Ins. will have 

 a capacity of 0.002 mfd. XIne of these plates, 

 connected In parallel, will total 0.018 mfd. If as 

 assumed, the potential of the transformer is 

 20,000 volts, a series-parallel connection for the 

 plates is required, that Is to say, 18 of these 

 plates must be connected In parallel In each bank 

 and the two banks connected In series. 



The Use of Loading- Coils 



E. C. T., Beaumont, Texas, inquires: 



Q. I. Approximately what is the wave- 

 length adjustment possible with a double-slide 

 tuning-coil 18 Ins. In length, 3 tJ Ins. in diameter, 

 wound with Xo. 22 S.C.C. wire? 



A. I. Connected to the average amateur 

 aerial this coil should permit adjustments to 

 stations employing wavelengths as great as 3000 

 or 3,500 meters. 



Q. 2. Would I secure better results If the 

 coll were wound with bare wire? 



A. 2. X'ot necessarily, since either bare or 

 Insulated wire may be employed. This coil Is too 

 large for the maximum degree of efficiency at 

 wavelengths lying between 200 and 1,000 meters. 

 For the ordinary aerial a single coil of wire, 6 Ins. 

 In length by 3 Ins. In diameter wound with No. 26 

 S.S.C. wire, will be sufficient for the lower value 

 of wavelength. 



Q. 3. Will a pancake loadlng-coIl Increase 

 the wavelength of the above tuning-coil? 



A. 3. Yes, but we see no need for it. 



Q. 4. How Is the loading-coil to be con- 

 nected to the tuning-coil? 



A. 4. It should be connected In series with 

 slidlng-contact connected to the aerial wires. 



Ground Connection 

 P. V. D., Warwick, X\ D., Inquires: 

 Q. What form of earth connection is con- 

 sidered desirable where the sub-soil consists of 

 hard and very dry clay? 



A. If by digging to a depth of several feet 

 moist earth cannot be reached, you are advised to 

 Install what is known as a "surface ground." 

 For your purposes this artificial earth connection 

 may consist of several long copper wires spread 

 out radially from the base of the mast and the 

 greater portion placed directly underneath the 

 flat top portion of the aerial. There should be at 

 least as much wire in this "ground" as there is in 

 your antenna. 



790 



