S

POLYSTYRENE BEAD

POSITION OF EFFECTIVE OPEN CIRCUIT

Figure 9. Cross-section diagrams of the Type 874-WN3 Short-Circuit Termination and the Type 874-W03 Open-Circuit Termination.

can be readily computed or compensated.

The Type 874-M Component Mount has been designed with these objectives in mind. It provides a shielded enclosure of convenient size within which a component can be mounted in a variety of ways, thereby enabling the user to approximate a circuit environment closely. Mounted on a Type 874-B Coaxial Connector, it connects to a Type 874-LB Slotted Line or Type 1602-A Admittance Meter through a smooth 50-ohm coaxial system that makes correction or compensation for "lead" length simple and straightforward.

A sketch of the mount is shown in Figure 8. The end of the center conductor of a section of 50-ohm air line is used as the ungrounded terminal and the outer conductor is extended in the form of a disc for a ground plane. The unknown is connected between the center conductor and the ground plate. It is connected by screws or binding posts, which are provided. Several mounting holes are arranged on the ground plate to provide a variety of spacings — M> inch, % inch, 1 inch, and inch. If necessary, a larger ground plate can be installed or the ground plate can be removed entirely and the center unit mounted directly on the device under test. The shield cover isolates the unknown from external electrostatic or electromagnetic interference.

To correct for the effect of the coaxial line connecting the measuring point and the component to be measured, one must know the line length accurately. The line length can be determined most readily by an impedance measurement with the line terminated in a short or open circuit at the terminals to which the component is to be connected. A low-inductance disc, supplied with the unit, can be screwed into the center terminal in place of the unknown to short-circuit the system at the ground plane.

Alternatively, to avoid the need for disconnecting the component to be measured from its mounting, the entire component mount can be unplugged and a Type 874-WN3 Short-Circuit Termination or a Type 874-W03 Open-Circuit Termination can be substituted. These terminations, supplied as accessories, place a short or open circuit at a distance of 3 cm. from the bead in the coaxial connector, a distance equal to that between the bead and the ground plane in

Figure 10. View of the component mount plugged into a General Radio slotted line for the measurement of a resistor.

Figure 10. View of the component mount plugged into a General Radio slotted line for the measurement of a resistor.

100 600 FREQUENCY, Me

the component mount. These units are shown in Figure 9.

The effect of the coaxial line can be calculated from transmission-line equations or read from a Smith chart; or it

Figure 11. Frequency characteristics of two composition resistors as measured with the Type 874-M Component Mount, the Type 874-LK Constant-Impedance Adjustable Line, and the Type 1602-A Admittance

Meter.

can be eliminated by inserting a Type 874-LK Constant-Impedance Adjustable Line between the measuring device and the component mount. The Type 874-M Component Mount is well suited for measurements on resistors, capacitors, inductors, anil other small components. Figures 1 and 10 show the component mount with the General Radio Slotted Line and Admittance Meter. Figure 11 shows the results of a set of measurements made with the Type 874-M Component Mount and the Type 1602-A Admittance Meter.

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