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Popular Science Montldy 



Receiving Wavelength 



C. H., Farniington, Conn., inquires: 

 Q. 1. A|)proxiinately to what wavelength can 

 I adjust with a tuning coil 20 in. in length, 2} in. 

 in diameter, wound with No. 30 bare wire? The re- 

 mainder of the apparatus comprises a condenser, 

 a galena detector and i5(K)-ohm telephones. 



A. 1. With the average amateur aerial this 

 tuning coil will permit adjustment to wavelengths 

 inclusive of 6,000 meters, and by the addition of a 

 condenser in shunt to the terminals of the 

 detector circuit, the wavelength can Ix' furl her 

 increased. 



Damped Wave Reception on 

 Oscillating Audion 



J. B. E., Newark, N. J., writes: 



Q. 1. Referring to the article by W. Ross 

 McKnight in the April, 1916, issue of the Popular 

 Science Monthly (page 613) 1 would like to know 

 if this equipment will respond to both dampeil 

 and undamped waves, that is, will the equipment 

 respond to ordinary spark stations without 

 change of circuit. 



A. 1. The receiving apparatus described by 

 Mr. McKnight is applicable to the reception of 

 both damped and undamped oscillations, but is 

 more sensitive with the latter. When tlie audion 

 is in a state of oscillation, an impure beat-nole is 

 produced in the reception of damped oscillations. 

 The result is that the s|)ark note of the distant 

 transmitting stations is distorted, the signal 

 sound being of different character and usually 

 lower than the normal note. The receiver 

 described by Mr. McKnight was built expressly 

 for the reception of long wavelengths and will not 

 give good results on the shorter wavelengths in 

 the vicinity of 600 to 1,000 meters. 



Long Distance Stations 



S. W. D., Hamilton, Ohio, inquires: 

 Q. Please give the wavelength, type of trans- 

 mitting apparatus, and the call letters of as 

 many as you can of the following Transatlantic 

 stations: 



Strength of Received Signals Where 

 Connecting Leads Are Long 



1). r. I)., I.imon, Colo., inquires: 



Q. 1. Will there be any loss in the loudness 

 or in the strength of signals when the receiving 

 apparatus is located 20 to 25 ft. from the light- 

 ning switch, the latter being erected on the out- 

 side of the building, and the receiving instru- 

 ments placed on the opposite side of the room to 

 that at which the lead is brought in from the 

 lightning switch? 



A. 1. No; it is of course desirable to make 

 the connecting lead as short as possible, but the 

 loss in efficiency will not be appreciable. 



Q. 2. What cfTect will it have on the strength 

 of wireless telegraph signals if the antenna and 

 ground wires are run parallel; that is to .say, are 

 twisted together for a distance of from 20 to 25 

 feet from the lightning switch to the receiving 

 apparatus? 



A. 2. The twisted cable will have distributed 

 capacity and will act as a condenser connected in 

 shunt to the primary winding and consequently 

 will occasion a loss in the strength of the signals. 

 It would be better to separate these wires by a 

 distance from 6 to 8 feet. 



Q. 3. My receiving aerial is 60 ft. in length 

 composed of five wires spaced three feet apart. 

 It points east and west. The lead-in is taken oft 

 the east end and extends to the lightning switch 

 which is mounted on the outside of the window 

 of the second floor. The distance from the (loint 

 where the lead-in is taken off cast to the lightning 

 switch is go ft. Could 1 get better results if the 

 lead-in was taken from the center of the aerial 

 instead of from the end? 



A. 3. For general receiving purposes it had 

 better remain as it is. 



Q. 4. Will the above aerial be satisfactory to 

 receive from the amateur stations, providing a 

 variable condenser is used to adjust the shorter 

 wavelengths? 



A. 4. Yes, if the condenser is in scries with 

 the antenna. 



Q. 5. What is the wavelength of this aerial? 



A. 5. The wavelength is close to 150 meters. 



Type of Appanilus 

 Goldschmill High Frequency Alternator 

 Joly lligli l're(|uency Allern;ilor 

 I)ain|)ed and Undamped Transmitters, Type 



L'nknown 

 Poulsen Arc Generator 

 Poulsen Arc Generator 

 Quenched Spark Transmitter 

 Marconi Rol:iry Disk Pischargcr 

 Marconi Rotary Pisk Discharger 

 Goldschmill High l-"re(|uency Alternator 

 500 Cycle Transmitter j K.W. 

 Joly High I'requeiicy Alternator 

 M;irconi RoMry Disk Discharger 

 Poulsen Arc Generator 



Wavelength (MclfTs) 

 7400 

 9400 



2500 (for time signals) 

 1 0000 



(XXX)- 1 (KXK) 

 300, (XX), I (XX) 



7<)25 

 2800 



7400 



3(X), (lOo 



c)4<«) 



8(xx), I ,sooo 



(XXKl 



