4-20
888-2586-001
9/15/06
WARNING: Disconnect primary power prior to servicing.
Platinum Z16HD+
Section 4 Overall System Theory
the isolation resistor for the 2-way Wilkinson combiner. Each Isolation Board has a pair
of ID jumpers, JP1 and JP2, which have to be set to designate into which Z-Plane that
particular Isolation Board is plugged. Proper setting for each Z-Plane is on the
schematic and silk-screened on the PC board.
The isolation resistors for the four way combiners, R1-R8, are each 50 ohm, 12 watts.
When all modules are working properly, these resistors dissipate little or no power.
However, when a PA fails approximately half of the power of one module will be across
the isolation resistor. The resistors will handle the imbalance of a failed module for
about 20 seconds. Therefore when a module has failed, the isolation resistor will start to
heat up. This rise in temperature is detected by a thermistor, T1-T8, which is physically
attached to the resistor. The thermistor output is sent to the associated PA Controller
Board (there are four). If the temperature gets too high, the PA Controller then shuts off
the module RF output via the PA gate voltage and activates the associated RF
disconnect switch on the isolation board. The RF switch disconnects the isolation
resistor and grounds that point in the combiner (E1-E8). This changes the 4 way
combiner into a 3 way combiner with a slight mismatch but is well within the ratings of
the modules. The effects are minimized by the 2 way combiner and its isolation resistor,
which will tend to absorb imbalances, and by the characteristics of the 3dB hybrid
combiner, which tends to ignore minor amplitude and phase imbalances in the two Z
Plane outputs.
The 2 way combiner combines the outputs of the 2 foursomes with the four in the front
being one foursome (such as A1-A4) and the four in the back being the other (such as
A5-A8). An imbalance between these 2 foursomes will cause a rise in the temperature
of RT9, the ISO load for the 2 way combiner, which is called Az, Bz, Cz and Dz for the
different Isolation Boards in the Diagnostics Display. R9 is a 400W ceramic resistor
mounted in the middle of the Isolation Board. For a detailed procedure for removing
and/or replacing the Isolation Boards refer to Section V, Maintenance.
4.4.6
"5kW" 3 dB Hybrid Combiners
The 3dB hybrid combiners are located in between each pair of Z Planes, AB and CD.
The outputs from each pair of Z-Planes are summed in the two 3dB hybrid combiners.
The entire assembly consisting of 2 Z-Planes, 8 modules and the 3dB hybrid combiner
in between is considered a Power Block. Since the RF inputs to the two Z Planes,
driving the PA inputs, come from the 3dB hybrid splitter on the IPA Backplane Board,
they differ in phase by 90 degrees. Thus, the outputs from the Z Planes differ by 90
degrees, allowing them to be combined in the 3dB hybrid output port with very little
power appearing at the reject load.
If the two Z Plane outputs are not equal, or are not exactly 90 degrees apart in phase, a
portion of the power appears to the reject load, however the 3dB hybrid is a very
stable device which sends most of the input power to the combined output over a fairly
wide range of input power ratios and input phase differences. The reject loads are 50
ohm 800 watt resistors mounted on a heatsink which is located on the upper end of the
Summary of Contents for Platinum Z16HD+
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