Bird Technologies 8650B Series - Manual (Page 28)

Bird 8650 Series Moduload RF Load Resistor
16
RF Load Resistor
Measuring DC Resistance
Accurate measurement of the DC resistance between the inner and outer con-
ductors of the RF input connector will provide a good check of the condition of
the load resistor. Checking the DC resistance measures changes in the condi-
tion of the resistor over time. Tracking the DC resistance must start before the
resistor is first put into service.
z Equipment Needed:
z
Common hand tools
z Ohmmeter with an accuracy of ±1% at 50 ohms
Note: Temperature of the load needs to be between 20°C to 25°C
(68°F to 77°F).
1. Turn off RF power and interlock circuitry before making any electrical dis-
connections.
2. Disconnect RF coaxial line.
3. Connect the multimeter test leads to the load resistor:
z One lead to the center conductor.
z One lead to the outer conductor.
4. Record the value of the resistance before the load is put into service.
5. Compare subsequent values with the latest reading.
Note: If the values vary more than 2 ohms this could be an indica-
tion of a failing resistive element.
Note: It is recommended that this resistance check be performed
each time the load is to be used.
Figure 10 Measuring DC Resistance
WARNING
Never attempt to connect or disconnect an RF transmission line while
power is on at the RF power source. Radiated RF energy is a potential
health hazard.