Oil Cooled RF Termination (250W)
The Bird 8141 RF Load is a portable, self-contained general purpose 50-ohm coaxial transmission line termination requiring no outside power source or additional equipment. It provides accurate, dependable, and practically non-reflective termination for testing and adjusting transmitters under non-radiating conditions.
The 8141 will absorb and dissipate as heat up to 250W of RF power in continuous duty. It can handle up to 20 percent overload for a maximum of ten minutes overload without damage, provided a half-hour interval is maintained for cooling between power applications.
VSWR is as follows:
- DC to 1 GHz @ 1.10 (max)
- 1 to 1.8 GHz @ 1.20 (max)
- 1.8 to 2.5 GHz @ 1.30 (max)
The 8141 is compatible with Bird Quick Change “QC” connectors.
Only a coaxial cable with the appropriate connector plug is needed for connecting these load resistors to the source of RF power.
Theory of operation
The Bird 8141 consists essentially of a cylindrical film-type resistor immersed in a dielectric coolant. The resistor, individually selected for its accuracy, is enclosed in a special tapered housing which provides a linear reduction in surge impedance directly proportional to the distance along the resistor. This produces the uniform, practically reflectionless line termination over the stated frequencies of the load.
The dielectric coolant is chosen for its desirable electrical properties and thermal characteristics. Cooling of the load is accomplished by natural fluid and air convection. The dielectric coolant carries the electrically generated heat from the resistor to the walls of the cylindrical cooling tank. The tank is encased in a set of heavy gauge aluminum radiator fins, which are firmly pressed on the cylinder. The heat from the dielectric oil is transferred to the surrounding air through the fins by natural convection.
A synthetic rubber diaphragm located in the rear dome of the load allows for the expansion of the coolant as the temperature rises.
Many models available
Bird offers several models of oil-cooled loads. Models are available with power ratings from 150W to 10kW, many connection options, and utilizing convection or blowers for cooling.
For more detailed information on Bird oil-cooled loads with power ratings, connector types, and more, please see pages 88-89 (PDF pages 9-10) of the document linked here.