TABLE OF CONTENTS One important class of instruments displays data electronically on a SMITH CHART. Some of these instruments employ a translucent SMITH CHART attached to the face of a cathode ray tube; others employ an opaque SMITH CHART on an electrically operated plotting table. In either of these the chart serves as the reference coordinate system. Such devices generally sample the amplitudes and phases of forward- and backward-traveling waves, respectively, at the output ports of a directional coupler. The samples are translated by sine and cosine function generators to control the position of the cathode ray spot, or of the pen on the plotting table. By using sweep-frequency oscillators such devices can display a large amount of data in a brief interval of time. Their detailed features and operation are best described by the individual manufacturer.
Other types of SMITH CHART "instruments" which are described herein are purely mechanical in operation, and are thus more analogous to the ordinary logarithmic-scaled slide rule.
The calculator shown in Fig. 14.1, constructed in 1939, employs a pair of cardboard disks, and a radial arm pivoted from the center. This arrangement allows separate control of the zero position on the outer peripheral scales which were printed on the larger disk, and the position of the radial arm with its attenuation and SWR scale (expressed as a ratio less than unity). A slidable cursor permits the establishment of reference points on the chart coordinates. This calculator, currently out of print,...
