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Page:Popular Science Monthly Volume 89.djvu/650

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What Radio Readers Want to Know

��Calculating Wavelengths; Circuits of

Audion Amplifier ; Helix for

Spark- Coil

E. B., Pittsburs, Pa., inquires:

Q. I. I have a loading coil for an inductively coupled receiving luner consisting of 625 turns of No. 22 enameled wire wound upon a tube 5J in. in diameter, also a secondary loading coil wound with No. 27 enameled wire for a distance of 7 in. on a similar size tube. Approximately what is the wavelength of each?

A. I. We cannot give the possible wave- length adju.stment of a coil without knowing the constants of the circuit in which it is to be employed. It is easy to calculate the natural wavelength, but this data would be of no value for ordinary usage. The primary loader has inductance of approximately 12,400,000 centi- meters and the other coil about 15,875,000 centimeters (15,875 microhenries). You of

��l)ut with .001 microfarads in shunt the wave- length of the circuit is about 7000 meters.

Q. T,. I require two loading inductances for this set to be adjustable to 14,500 meters in steps of 500 meters at a time; but they cannot occupy a space more than 8 in. by 5 in. by 3 in. Can you supply the data for the windings?

A. 3. We know of no method by which you can obtain this value of wavelength with a coil of these dimensions unless you wound it with very fine wire which, of course, would make them useless. Also keep before you the fact that there are no stations in o[)eration that use the wavelength of 14,500 meters. Why not con- struct a set like that described by McKnight in the April, 191C, PopirLAR Science Monthly?

Q. 4. Can you furnish me with the circuits of the single step Audion amplifier?

A. 4. See the accompanying diagram.

Q. 5. What is the voltage of the filament battery?

���Diagram showing the circuits of the single step Audion Amplifier

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��course understand that the increase in wave- length to be obtained with a given loading coil depends upon the natural inductance and capacity of the circuit in which it is to be con- nected; consequently, if these values are un- known, no general estimate can be given. You will then see that there is no such thing as a "2800 meter loading coil" even though manufac- turers are prone to use the notation.

Q. 2. My Navy type receiving tuner has a primary winding consisting of a single layer of No. 20 enameled wire wound upon a tube 4i in. in diameter for a distance of 5 in. The second. iry tube is 3J in. in diameter, wound for a distance of 5 in. with No. 30 enameled wire. What is the maximum wavelength this tuner will respond lo?

A. 2. Lacking the dimensions of the aerial it is difficult 1(1 .nlvise; but with one of the usual am:ilcur dimensions, the primary circuit is adjustable to waves of 45<m) meters. With a capacity of .o<k)I microfarads in shunt, the secondary < ire nil will r<s|K)n(l to 2400 melcrs

��A. 5-

Q. 6.

battery?

A. 6.

Q. 7. A. 7. Q. 8.

��4 volts.

What is the voltage of the second

��25 to 45 volts.

Is the Audion tube suitable for this ? Yes.

Can you give me the voltage of the telephone battery in the RJ5 Audion?

A. 8. 25 to 45 volts.

Q. 9. What type of battery cell is used?

A. q. A 20-ampere hour storage cell for the filament and 10 tungsten flashlight cells for the telephone battery.

O. 10. Mow many turns of edgewise wound copper ribbon 7J in. inside ciiameter, 8J in. outside diameter, 1-16 in. in ihickne^is, are required as a helix for a yin. spark coil?

A. 10. The helix rc(|uiros 10 turns of the copixT spaced 5 in. apart. A condenser of .tH)2 mirrofar.ids is sufTicient. A single plate of gl.iss 14 in. by 14 in. covered with ihin foil 12 in. by 12 in., the glass iK-ing J in. in thickness will give the required value of c-ijiacity.

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