An automatic Smith diagram display unit for use at low power levels

An equipment is described whose primary purpose is to display variations in the r.f. admittance of low-level detector crystal valves during the adjustment process. For this purpose the input power level must not exceed about 5¿W. The method is not, however, limited to this application but may be applied to microwave transmission systems generally. Information relating to the r.f. admittance is derived from four detector probes mounted with spacings of 3¿/8 along a standing-wave detector carriage. This is utilized electronically to actuate the deflecting plates of a cathode-ray tube in such a manner that a direct display of the Smith diagram is obtained on the face of the tube. The above principles are incorporated in an equipment operating at 3.2cm, but with an appropriate 4-probe standing-wave detector this could be used at any wavelength.