2-36Figure 2-29.—Decade resistor.DECADE (STEP) ATTENUATORSDecade attenuators (also referred to as step attenuators) are common devices that may be designed aseither a stand-alone piece of test equipment or as an integral part of an operational piece of electronicequipment. As the name implies, they are used to attenuate rf signals in incremental steps. Like the fixedrf attenuator, you can easily test them by using the rf substitution method, as previously described. ViewsA and B of figure 2-30 show two types of decade attenuators.Figure 2-30.—Step attenuators.50/75-OHM TERMINATIONSTerminations of 50 and 75 ohms are designed as either feedthrough, impedance-matching devices, oras rf loading devices. They are precision resistors sealed in small plastic or metal enclosures and aredesigned to be mounted on various rf connectors. In the case of feedthrough terminations, they aredesigned with rf connectors at both ends, which allows the rf signal to pass through them. They areimpedance-matching devices designed primarily to reduce the voltage standing-wave ratio (vswr) that isproduced when two pieces of equipment with dissimilar impedances are connected together.You can test a feedthrough termination by measuring the resistance between the center conductorand the shield of either rf connector with an ohmmeter. As mentioned above, some terminations aremanufactured as loading devices that are designed to shunt an rf signal to ground. A perfectly matchedtermination can be compared to a transmitting antenna in that it absorbs all of the rf signal with only a
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