What Radio Readers Want to Know 



When Is the Transmitter in 

 Good Condition ? 



Ricardo Moran Percira, Guayaquil, Ecuador, 

 S. A.: 



The information you request concerning the 

 operation of wireless telegraph equipment is 

 mainly covered in the various textbooks of wire- 

 less telegraphy, but not specifically taken up in 

 any particular one. The necessary tests for 

 determining the condition of radio telegraphic 

 apparatus are so well understood by those 

 engaged in the work that the authors have 

 neglected to take up this phase of the subject. 



The condition of the secondary winding of a 

 high potential transformer may be tested in the 

 following manner; Connect a small spark-gap 

 in shunt to the secondary winding and supply the 

 primary winding with correct value of potential. 

 If a good fat spark discliarge is not secured at the 

 secondary terminals even when the gap is of 

 excessively short length it is an indication that 

 all or a portion of the secondary winding is short- 

 circuited. 



The open circuit in the primary winding of a 

 transformer may be determined by connecting a 

 l6-candlepower incandescent Edison [lamp in 

 series with the circuit. If the lamp does not 

 glow it indicates that the circuit is open. If the 

 primary winding is short-circuited the fuses will 

 blow whenever the circuit is closed. 



A breakdown of the high potential condenser 

 is generally directly visible. 



Violent brush discharge at the condenser is an 

 indication of excessive voltage or a spark-gap of 

 too great length. It is also sometimes due to the 

 irregularities in the coatings which may have 

 jagged edges. To some extent brush discharge 

 can be prevented by immersing the condensers in 

 oil or by the use of a series-parallel connection, 

 thereby dividing the potential between several 

 banks. 



Regarding the matter of induced potentials 

 from the aerial system, in any radio installation 

 ever)' effort should be made to keep the low 

 potential power wires at a distance from the high- 

 frequency circuits. In any event the low 

 potential power mains should be placed in the 

 iron conduit, the latter being directly connected 

 with the earth. 



The condenser is prevented from discharging 

 into the secondary winding by means of high- 

 frequency choke-coils which generally consist of 

 lour to ten turns of copper wire wound in the 

 form of a pancake s[)iral with the turns spread 

 about I in. The inductance of these coils has 

 little effect upon the potential of the secondary 

 winding but offers a very high impedance to the 

 high-frequency currents of the condenser. 



The dimensions of the condenser are limited 



by the wavelength to be employed. In the case 

 of a I k.w. sat operated from a source of 60 

 cycles, it is customary to use a condenser having 

 capacity of .012 microfarads; 2 k.w. sets employ 

 capacities varying from .018 microfarads to .036 

 microfarads. 



To go into these matters more in detail would 

 reqi ire the space of a small textbook, and we 

 believe that your queries taken as a unit are best 

 answered in a publication entitled "Textbook of 

 Wireless Telegraphy" by Rupert Stanley. This 

 book is probably the most up-to-date one on the 

 subject, as it gives the theoretical principles and 

 the practical details of modern commercial 

 telegraph apparatus. 



Receiving 3,000 Miles 

 I. E. R., Cuenca, Ecuador, writes: 

 Q. I. Can you give the dimensions and the 

 best type of an aerial for the reception of signals 

 to a distance of 3,000 miles? This aerial is to be 

 used with the Navy type of loose-coupler. 



A. I. If this aerial is to be employed for 

 wavelengths up to 3,000 meters from stations 

 using damped oscillations, the flat top portion of 

 the aerial may consist of four wires spaced 2 2 ft. 

 apart, 350 ft. in length, and from 120 to 200 ft. 

 in height. 



Q. 2. What is the least expensive detector 

 that could be used for the purpose.-* 



A. 2. Any of the detector minerals such as 

 galena, cerusite, molybdenite, silicon and car- 

 borundum are inexpensive. The audion is the 

 most sensitive detector in existence, but of 

 course is more expensive than any of the fore- 

 going. 



Flickering of Lights 



E. B., Ccntralia, III., inquires: 



Q. Why should a J k.w. transformer maki^ 

 the lights flicker, and what can be done to 

 remedy this? 



A. When the condenser connected in shunt to 

 the secondary winding of the transformer dis- 

 charges across the spark-gap, the secondary 

 winding is temporarily short-circuited, and 

 unless the magnetic circuit of the transformer is 

 arranged to have a certain amount of magnetic 

 leakage, the primary winding will draw an 

 excessive value of current. Vou may perhaps be 

 able to lessen this effect by changing the capacity 

 of the condenser or by inserting a reactance coil 

 in series with the primary winding. It is also 

 possible to connect a reactance coil in shunt to 

 the telegraph key. When connected in thl.^; 

 manner a portion of the energy constantly flows 

 into the primary winding, and the remainder or 

 the full intake flows when the key is depressed. 

 This method has often been found to assist 

 matters materially. 



14J 



