To Bottom of Page
Return to Table of Contents
The chart on th 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
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.
The direct-reading charts appearing on the following
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
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.
Return to top
Return to Table of Contents