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The chart on the opposite page provides a convenient means of determining the unknown factors of small sized single-layer wound r-f coils. Values thus found so cosely approximate those determined by measurement or mathematical calculation as to be entirely satisfactory for all practical purposes of experimentation, design, and repair work. Since in all coils of this type, the difference between the mean and inner diameter of the winding is so slight as to be negigible, D in all instances may be either the mean or inner diameter as desired. Example: Given the total number of turns, winding length and diameter of a coil, -- to find the inductance: 1. Place a straightedge on the chart so as to form a line intersecting the number of turns N, and the ratio of diameter to length K, and note the point intersected on the linear axis column. |
2. Now move the straightedge so as to form a second line which will intersect this same point on the axis column, and the diameter D. 3. The point where this line intersects the L column indicates the inductance of the coil in microhenries. Example: Given the diameter, winding length and inductance in microhenries, -- to find the number of turns; 1. Simply reverse the process outlined above for determining inductance. 2. After finding the number of turns, consult the wire table on page 35 and determine the size of the wire to be used. The dotted lines appearing on the chart illustrate the correct ploting of a 600 microhenry coil consisting of 100 turns of wire wound to 51/64" on a form 2" in diameter. |
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The direct-reading charts appearing on the following
three
pages are designed for determining unknown values of frequency, inductance, capacitance and reactance components operating in a-f and r-f circuits. The simplifications embodied in these charts make them extremely useful. The frequency range covered comprises the frequency spectrum from 1 cycle per second up to 1000 megacycles per second. All of the scales involved are plotted in actual magnitudes so that no computations are required to determine the location of the decimal point in the final result. To make these conditions possible the frequency spectrum has been divided into three parts: Chart I (page 38)--Covers the range from 1 cycle to 1000 cycles. Chart II (page 39)--From 1 kilocycle to 1000 kilocycles. Chart III (page 40)--From 1 megacycle to 1000 megacycles. Inductance, capacitance, reactance and frequency have been plotted so that the reactance offered by an inductance at any frequency may be readily determined by placing a straight-edge across the chart connecting the know quantities. Since XL = XC at resonance in most radio circuits, the charts |
may also be used to find the resonant frequency of any combi-
nation of L and C. To illustrate with a simple example, suppose the reactance of a 0.01 uf. capacitor is desired at a frequency of 400 cycles. Place a straight-edge across the proper chart so as to connect the points 0.01 uf. and 400 cycles per sec. The quantity desired is the point of intersection with the reactance scale which is 40,000 ohms. The straight-edge also intersects the inductance scale at 15.8 henrys indicating that this value of inductance likewise has a reactance of 40,000 ohms at 400 cycles per sec. and furthermore, that these values of L and C produce resonance at this frequency. There are many practical uses for these charts. The radio experimentor, maintenance man and engineer will find them helpful in the rapid solution of many reactance problems. Unusual care was exercised in laying out the various scales in order to secure a high degree of accuracy for the charts. Results should be obatinable which are at least as accurate as might be secured with a ten-inch slide rule. |
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