Small Components Used in Radio Frequency Test and Measurement

This chapter discusses some of the common devices that are used for radio frequency (RF) tests and measurements. An attenuator is a device that reduces the amplitude of an applied signal. Most commercially available attenuators are shielded, and the shield is grounded even if the circuit inside it is balanced. A dummy load is a resistive load with a specified resistance value. It is used to terminate ports that are unused. The chapter illustrates the basic circuit of a dummy load through diagrams. It consists of a noninductive resistor inside a shielded enclosure, with a coaxial connector to provide access. It is very important that the resistors have a value equal to the desired system impedance. The power rating of the dummy load should be sufficient to prevent resistance changes because of self-heating. In many cases, a half-watt dummy load is usable, but if significant amounts of RF power are anticipated, a higher rating is required. When transmitters are tested, it is a common practice to use a dummy load to absorb the generated RF power. The chapter concludes with a discussion of directional couplers.