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Page:Popular Science Monthly Volume 90.djvu/335

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What Radio Readers Want to Know

Interesting and Instructive Questions and Answers

��Loading Coil for an Aerial to Receive on Long Waves

W. L., Secaucus, N. J., writes:

Q. 1. I have an aerial 75 ft. in length, 18 ft. in height at one end and 25 ft. in height at the other end. Please state the natural wavelength. It has four wires spaced two feet apart.

A. 1. The wavelength of this aerial is approxi- mately 165 meters.

Q. 2. Is it possible to load this antenna to the wavelength of 6,000 meters?

A. 2. For receiving purposes it is practical.

Q. 3. Please give the necessary dimensions for a loading coil for this aerial.

A. 3. Wind up a cardboard tube 6 in. in diameter, 24 in. in length, with No. 24 S. S. C. wire, and bring taps from the winding every inch. You will then have no difficulty in boosting the wavelength of this antenna to 6,000 meters.

��Inductively Coupled Tuner of 11,000 Meters

M. D., Newark, N.J., inquires:

Q. 1. Please give me the dimensions for an inductively coupled receiving tuner to be adjustable to a wavelength of 1 1 ,000 meters. How many taps are required on each winding?

A. 1. The secondary winding of this tuner may be 15 in. in length, 7 in. in diameter, wound closely with No. 32 wire; the corresponding primary winding may be 73^ in. in diameter, 15 in. in length, wound closely with No. 24 S. S. C. wire. The turns of the secondary winding should be equally divided between the contact points of a ten point switch, while those of the primary winding may be wired either by means of two multipoint switches or by a sliding contact. For this equipment you should have two variable condensers of .001 microfarads capac- ity, one being placed in shunt with the primary winding on the receiving tuner and the second in shunt to the secondary winding.

��heard when the batteries are connected thereto. Can you advise a remedy for our troubles?

A, 1. One thing is certain, when the motor gen- erator is connected to the storage batteries there must be a fluctuation of the line current, and con- sequently it sets up inductive noises in your receiver. It may be that the commutator of the motor generator set sparks badly. A similar case of induction was eliminated in the following manner: The power leads from the motor generator to the storage battery were placed in an iron conduit and the iron conduit firmly connected to earth. In addition two condensers of two microfarads capacity each were connected in series and earthed at the center point. The other terminals were shunted across the storage battery.

��Connections for a Three Slide Tuner with Other Apparatus F. H. M., Richmond HiU, N. Y., inquires: Q. 1. When do Sayville, Arlington, Tuckerton, and the Brooklyn Navy Yard send out messages, and what is their wave- length?

A. I. The wavelength of Sayville is 9,400 meters ; Arlington 2,500 meters for the spark set and 7,000 meters for the arc set;

��AERIAL

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��Diagram of connections for a three slide tuner, galena detector, loading coil, fixed condenser and variable condenser

��Induction Interference from a Neighboring Motor

C. V. H., Kinsley, Kansas, writes:

Q. 1. We have been using a wireless set for the reception of time signals for over a year. During this period we have experienced no interference of any sort, but quite recently a garage about one block away installed a motor generator for charging storage batteries. When the batteries are being charged the induction is so bad we are unable to read a signal. The difficulty does not seem to lie with the motor generator, for the interfering noises are only

��Tuckerton 7,400 meters; Brooklyn Navy Yard 600 and 1,000 meters. Sayville and Tuckerton may be heard any evening between the hours of seven and twelve P. M. eastern standard time, while Arlington may be heard at 12 noon and 10 p. m. eastern standard time, using the spark set at the wave of 2,500 meters. The Brooklyn Navy Yard com- municates at irregular intervals with other Naval stations throughout the entire day.

Q. 2. Please give a diagram of connections for the following apparatus: Three slide tuner, galena detector, loading coil, fixed condenser, and variable condenser.

A. 2. Diagram of connections is shown above.

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