320 



Popular Science Monthly 



Polarized Relay as Interrupter 



H. B. R., Monticello, Ga., inquires: 



Q. 1. Please advise if an electro magnetic 

 polarized relay will work successfully on no volt 60 

 cycle alternating current as a vibrator for an induc- 

 tion coil in the following manner: I propose to use 

 two armatures each having a contact which makes 

 connection with a stationary contact. Do you 

 consider this feasible? 



A. I . It is believed that you will find it extremely 

 difficult to adjust both contacts to interrupt the 

 circuit of each coil if they are mounted on a single 

 armature. However, by the use of separate arma- 

 tures for each set of contacts the proposition is more 

 feasible. Several experimenters within our knowl- 

 edge have tried o.ut the arrangement you suggest and 

 have reported results considerably inferior to the 

 ordinary induction coil vibrator. 



Receiving on the Static- Coupled Tuner 



J. M. S., Jr., New Castle Pa., writes: 



Q. 1. Referring to the static coupled receiving 

 set described on page 306 of the February issue of 

 your magazine, what should be the dimensions of the 

 coils L-i, L-2, and L-3, to make an equipment 

 adjustable to 5,000 meters, and to be used in connec- 

 tion with an aerial 175 feet in length, 50 feet in 

 height, composed of a single wire. 



A. 1. The fundamental wavelength of your 

 aerial is about 350 meters and all the inductance for 

 the antenna circuit may be included in the coil L-2. 

 Here a coil 3^ in. in diameter, 10 in. in length, 

 wound with No. 26 S.S.C. wire will permit the 

 desired value of wavelength. The coil L-2 should if 

 possible have about the same dimensions. It can of 

 course be made smaller, and a portion of the in- 

 ductance included at the point L-i, but we see no 

 reason for splitting it in this manner. 



Q. 2. Is a crystaloid detector as sensitive as any 

 crystal or electrolytic detector on the market? 



A. 2. Many experimenters report better results 

 from it than with the electrolytic. For the best 

 results the stopping condenser of the usual circuit 

 should be one of variable capacity and possesses 

 values up to or beyond 0.005 microfarads. 



Q. 3. How shall I connect a tikker in the 

 statically coupled receiving set? 



A. 3. Connect it in the circuit at the same point 

 as the crystal detector D. The condenser C-2 

 should then have rather large values of capacity, as 

 much as .05 or o.i microfarads. 



Q. 4. What wavelength does Arlington use with 

 the undamped wave transmitter, and should I be 

 able to hear the signals of the statically coupled 

 receiving set and a tikker. 



A. 4. By careful adjustment of the circuits to 

 resonance with the wavelength of 7,000 meters, you 

 should be enabled to receive the signals in your 

 home town, but the dimensions for the coils which 

 we have given will not permit this circuit to respond 

 to the wavelength of 7,000 meters. Increased 

 values of inductance must be added at the coil L-i. 

 We would advise a loading coil of No. 24 wire at L-i 



approximately 8 in. in length by 3 in. in diameter 

 fitted with a multipoint switch having taps about 

 every half inch. You would obtain better results 

 in the reception of signals from this station by using 

 some form of the oscillating vacuum valve. 



Ground Connections 



P. L. K., Somerville, Mass., inquires: 



Q. 1. What effect has a long earth wire on the 

 range of a radio set? Does it decrease the range? 

 Does it increase the wavelength? 



A. 1. The earth lead is a part of the open circuit 

 oscillator and consequently an increase in length of 

 it increases the effective wavelength of the entire 

 system. It is considered preferable in all radio 

 installations, particularly as far as the transmitting 

 apparatus is concerned, to make the earth lead as 

 short as possible, otherwise the range of the appar- 

 atus will be seriously decreased. 



Q. 2. I have an inverted "L" aerial 85 feet in 

 length, 30 feet in height. The ground Avire is no 

 feet in length. Do you consider my ground wire 

 abnormally long in proportion to the aerial? 



A. 2. For transmitting purposes your earth wire 

 is too long, but for receiving purposes the length is 

 not so serious. 



Q. 3. What is the natural wavelength of my 

 aerial? 



A. 3. About 300 meters. 



Q. 4. How may I reduce the wavelength? 



A. 4. By means of a series condenser or by 

 decrease in the length of the earth lead. It is con- 

 sidered sufficient for receiving apparatus to connect 

 the earth wire to water pipes inside the house. 



Sending Condenser 

 G. D., Ligonier, Ind., writes: 



Q. 1. I calculate that in order to obtain a capacity 

 of .008 microfarads, which I am told is the maximum 

 value that can be used at the wavelength of 200 

 meters, I will require 25 plates of glass 3132 in. in 

 thickness covered on each side with tinfoil 6 in. by 

 8 in. Is this correct? I fear that a single bank of 

 these plates will not be able to withstand the voltage 

 of the transformer. Consequently would it be 

 proper to use two banks of 25 plates each connected 

 in series? Furthermore, would this reduce the 

 liability of puncture? 



A. 1. Each plate of your condenser will have an 

 approximate capacity of .00066 microfarads. Twelve 

 plates connected in parallel will give you a value of 

 .008 microfarads. Therefore a 48-plate condenser, 

 24 plates in each bank and the two banks connected 

 in series, will give you the required value of capacity. 

 The placing of two banks in series reduces the 

 potential on the plates to one-half the value of a 

 parallel connection. 



Q. 2. Can you suggest any method by which the 

 plates can be coated to prevent brush discharge 

 without immersing them in oil? 



A. 2. You might cover the plates with a good 

 grade of beeswax or paraffin wax, but the best 

 method of course is to immerse them in oil. 



