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Page:Popular Science Monthly Volume 89.djvu/160

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146

��Popular Science Monthly

��Windings for Receiving-Tuner

P. K., Somervillc, Mass., inquires:

Q. I. Will a loose coupler having oval tubes for the primary and secondary winding be as efficient as one using round tubes?

A. I. Yes, practically so.

Q. 2. Which is preferable for the windings, cotton or enameled copper wire?

A. 2. Cotton wire is generally preferred to enameled wire, but it is the general practice in commercial apparatus to use single silk-covered wire.

Q. 3. Are No. 22 B & S and No. 32 B & S wire correct for the primary and secondary of an inductively-coupled receiving-tuner?

A. 3. Yes, but generally No. 24 or No. 26 is used for the primary winding.

Detailed Dimensions of a 3,000-Meter Tuner G. O. B., Kimbolton, Ohio, inquires: Q. 1. Please give explicit instructions for the construction of an inductively-coupled receiving- tuner for all-around amateur work, taking particular care to state the number of turns necessary for the primary and secondary wind- ings, also the number of taps to be taken from these windings.

A. I. For all-around amateur work, the receiving-tuner should be responsive to wave- lengths inclusive of 3,000 meters. The primary winding should be 52 ins. in length by 5 ins. in diameter, wound closely with about 300 turns of No. 26 wire. The secondary winding should be 5 ins. in length, 3;- ins. in diameter, wound closely with 500 turns of No. 32 wire. The inductance of the primary circuit may be altered by means of a multipoint switch or by a sliding- contact. It is customary to fit this winding with two switches in some tuners. For example: The first ten individual turns of the winding may be connected to a ten-point switch; the remain- ing turns are connected in groups of 10 to the contact-points of a second switch. In this instance you require a 29-point switch for the groups of ten turns. The turns of the secondary winding may be equally divided between the taps of a ten-point switch. This secondary winding should be shunted by a variable condenser of a small capacity, say .001 microfarads, for tuning.

Small Power-Transmitter

G. W., KIk City, Okla., inquires:

Q. 1. Will a spark-coil from an automobile have sufficient power to act as a wireless trans- mitter for a distance of two or three miles?

A. I. Yes, provided the potential is sufficient to jump a gap of at least J in.

Q. 2. Will telephone induction-coils serve the same purpose?

A. 2. Generally, no. If the potential of the secondary of the coil is sufficient to give a sm.dl

��spark-discharge, it may be used for extremely short distance work, but not otherwise.

Q. 3. Will a steel tower interfere with the reception of messages if the aerial is attached to it?

A. 3. No, not if the wires are swung out at a distance from the tower.

Receiving Aerial

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

Q. I. Please advise if an aerial of four wires 20 ft. in length by 20 ft. in height has sufficient dimensions to receive wireless telephone messages with an ordinary telephone receiver and a crystalline detector.

A. I. To begin with there are no wireless telephone transmitting stations in operation from which you could receive signals. The experiments at the Naval Station at Arlington to which you probably refer were conducted on a wavelength of 6,000 meters. Your aerial is entirely too small for adjustment to long waves. A single wire from 500 to 800 ft. in length could easily be loaded to a fundamental wavelength of 6,000 meters.

Long Wave Receiving Tuner

P. A. J., Jr., Suffolk, Va., writes:

Q. I. I propose to wind the coils for a receiving tuner on two tubes; one is II ins. in length by 6 ins. in diameter and the second 12 ins. in length by 5 ins. in diameter. What size wire should I use and to what range of wavelength will it be adjustable?

A. I. Use the ii-in. tube for the primary winding and cover it with No. 24 S.S.C. wire. Connected to the average amateur aerial, it will permit adjustments inclusive of 6,000 meters. 750 feet of wire are required for this winding.

The secondary w inding requires approximately 1,250 feet of No. 30 S.S.C. wire. Connected in shunt to a small variable condenser, it will respond to wave lengths between 8,000 and 0,000 meters.

Licensing of Sending Stations

R. D. S., Ripley, Okla., inquires:

Q. I. With a transmitting set composed of a i-in. spark-coil, small oscillation transformer and glass plate condenser, wovdd I recpiire a U. S. license if my station is located 65 miles from the State Line and 15 miles from the nearest radio station which is a college ex])erimenlal station located at -Stillwater? If a license is required please give the necessary instructions for obtaining it.

A. I. During the daylight hours the range of this ai)paratus will not exceed 20 miles and in consequence a license is not required. It is equally probable that the signals from this station will not extend over the State Line during the night hours.

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