Bird Technologies 8833-300 - Manual (Page 9)

istor housing mount furnishes a seal for the radiator
opening. A beveled flange retains the o-ring. The
o-ring is pressed against the radiator face by the
action of drawing up of radial V-band clamp around
the enclosing beveled flanges.
3.3 Radiator
When input power is applied, the resistor generates
heat which is absorbed by the surrounding dielectric
coolant. By convection, the heated oil flows through
holes in the coaxial shell to the walls of the radiator
tank. This radiator is a fabricated single-unit construc-
tion, and is carefully designed of heat-sink sections
on a unique vertical rhombic form. This provides a
very high efficiency of heat transfer from the dielectric
coolant into the surrounding air.
4. Operating Instructions
4.1 Load Resistor Connection
Warning
Provide adequate ventilation and observe normal
precautions when using dry cleaning solvents. Many
dry cleaning agents emit toxic fumes that may be
harmful to your health if inhaled.
Clean all conductors and insulator surfaces on the
transmission line face and check the RF input con-
nector. Use an aerosol type contact cleaner or any
dry cleaning solvent on a cotton swab stick, if nec-
essary.
Attach the Model 8833-300 Load Resistor to the RF
line with a 50 ohm coaxial cable such as RG-218/U
or RG-220/U (-17A or 19A) with a suitable plug
attached. Check that all coaxial power line connec-
tions are properly tightened. Avoid the use of adapt-
ers and elbows whenever possible.
4.2 Load Resistor Operation
Warning Never attempt to disconnect RF equipment
from a transmission line while RF power is being
applied. Leaking RF energy is a potential health
hazard.
Proceed according to the instructions pertaining to
the specific transmitting equipment. There are no
operating controls or adjustments for the Model 8833-
300 Termaline Load Resistor.
Due to the difference in VSWR between the dummy
load and the transmitter’s antenna, readjustment of
the transmitter may be required when returning to the
original antenna.
5. Maintenance
5.1 General
The Model 8833-300 RF Load Resistor is very rug-
ged and simple requiring little routine attention. The
load will operate for a long period of time if its power
handling capabilities are not exceeded.
Warning
Provide adequate ventilation and observe normal
precautions when using dry cleaning solvents. Many
dry cleaning agents emit toxic fumes that may be
harmful to your health if inhaled.
The outside surface of the unit should be wiped free
of dust and dirt when necessary. Clean the RF input
connector with an aerosol type contact cleaner or dry
cleaning solvent on a cotton swab stick. Take special
care to clean the metallic contact surface and the
exposed faces of the teflon insulator.
5.2 Checking the DC Resistance
VSWR and RF Impedance are the true benchmark
of a quality dummy load. Checking the dc resistance
is simply used to measure a change in the condition
of the resistor over a period of time. If the application
requires such measurements, follow the steps below
to obtain a benchmark value before the unit is put
into service, then periodically according to use.
Preparation and Tools Required
Be sure the vent plug is installed, see paragraph 2.4.
Tools: Resistance Bridge or Ohmmeter with accuracy
of ±1% @50 ohms.
Temperature of the load is 20° to 25°C (68° to 70°F).
Procedure
Using the resistance bridge or ohmmeter, check the
dc resistance of the load before it is put into service,
see Figure-6.
Compare the value to benchmark value obtained
during installation.
Normally the dc resistance of the load will be a
nominal 50 ohms. Stabilization of the resistive film or
temperature can cause a change in the dc resis-
tance.
If the values vary more than 2 ohms this could be
an indication of a failing resistive element.
5.3 Removing the Load Resistor
The load resistor assembly is not field serviceable.
In the event of a failure, the load resistor assem-
bly—complete—must be replaced.
RF Load Resistor Model 8833-300
Page 9