Specifications

4.5.1.5 RF Drivers
The RF Driver consists of fourteen Driver RF Amplifiers, D1
through D14. The RF driveinputs are fromthe PredriverSplitter,
and the RF outputs go to the RF Driver Combiner.
Thenumber of Driversused is determined by theDriverEncoder
board. All Drivers operate from +115VDC.
Drivers D1 through D7 are always turned on, D8 - D10 are
frequency determined Drivers and D11 - D14 are AGC Drivers.
By varying the number of Drivers turned on, the Driver Encoder
regulates the RF drive to the 160 RF Amplifiers.
These 14 Driver RF Amplifiers are interchangeable with the
Predriver and any of the 160 Big Step and Binary RF Amplifiers.
4.5.1.6 RF Driver Combiner
Each Driver RF Amplifier feeds its own ferrite toroidal com-
biner transformer primary and a copper rod passing through the
fourteen toroids acts as secondary windings connected in series.
The combiner toroids adds RF voltages from the Drivers as the
secondary passes from one transformer to the next. The RF
voltage is low or zero at the ground point of the secondary rod
and increases along the way to the RF Splitter.
4.5.1.7 Driver Tuning
The Driver Tuning Assembly provides variable inductive and
capacitive tuning to resonate the combiner pipe.
4.5.1.8 Boost Transformer
Toroid transformer T1 provides a frequency determined
boost/no boost step up action of the RF drive to the Drivers.
4.5.1.9 RF Drive Splitter A6 And RF Drive Cables
The purpose of the RF Splitter is to divide the combined output
of the Driver Combiner and provide each Big Step and Binary
RF Amplifier with the proper RF drive level.
The bottom end of the combiner rod bolts to theA6 board, which
contains a largeferrite toroid transformer and conductiveRF and
ground planes.
There are 20 connectors, J1 through J20, which provide a total
of 320 outputs, one for each half-quad on each of the 160 Big
Step and Binary RF Amplifiers. Each connector provides con-
nections for two sets of eight coaxial cables, the eight cables
from each connector form a cable bundle which goes to the input
connectors on Big Step and Binary Combiner Motherboards.
An additional connector J21 on the splitter assembly provides
RF sample signals to other parts of the transmitter, as follows:
a. A synchronizing RF signal for the A/D Conversion proc-
ess on the Driver Encoder.
b. An RF drive sample for Low Drive and High Drive Fault
sensor circuits, and the Relative RF Drive metering also
on the Driver Encoder.
4.5.2
Output Network Description
The Output Network transforms the impedance of the RF Com-
biner output, at about 8 Ohms, to 50 Ohms. This is done in two
basic sections, the Bandpass Filter stage and the Output Match-
ing stage.
The RF Output Network is contained in the Output Network
cabinet, see VIEW 19, 25, 26, & 27.
NOTE - The Output Sample boards and ARC Detectors are
detailed in Section H.
Refer to Figure 4-6, Output Network for the following descrip-
tion.
4.5.2.1 Bandpass Filter
The bandpass filter/output network is both a filter and an imped-
ance matching network. The combiner output impedance is low
(about 8 Ohms) and is matched or stepped up to 50 Ohms. The
bandpass filter section of the Output Network consists of L1 and
C1. L1 has switched amounts of inductance that is resonated
with C1 at the selected frequency. C5 (in the output network
cabinet) and C1 (5 9100 pF capacitors in parallel), C2, C3 and
C49 are used to resonate out the inductance of the combiner pipe
atthegroundend.C2andC3areswitchedbyrelaysK2andK3.
C49isswitchedbyrelayK4.
K3 and K4 are turned on / off by Bit0 logic from the frequency
control interface (1C1 Drive). K2 is controlled by Bit1 logic
also from the frequency control interface.
The bandpass filteralso smoothes the small steps that are present
in the PA’s output; the small steps result from sidebands outside
the audio frequency range which are attenuated in the filter. Any
other harmonic and spurious signals in the RF power amplifier
section output are also attenuated by the bandpass filter.
4.5.2.2
π Matching Network
The π Matching Network consists of C2, L2, C3, and C4. L2 is
a variable inductor that is varied by the LOAD Servo control.
C2 and C4 are comprised of a combination of capacitors in
parallel to form the input/output leg of the π network. C3 is
adjusted to resonate with L2 at 3fc. The parallel resonant circuit
provides further attenuation of the 3rd harmonic while passing
the carrier frequency. A static drain choke and arc gap provide
further protection at the RF Output connector.
4.5.2.3 RF Output Combiner RF Samples
A number of RF samples are picked up from various points in
the RF Combiner and distributed to circuits elsewhere in the
transmitter. (See VIEWS 15 & 19 for locations of the following).
T3 - Network Current Sample
At the ground point of the combiner, an RF current sample is
picked up by a current transformer and compared to the RF
voltage sample at the input of the Bandpass Filter. R5 is made
up of 4 two watt resistors in parallel to provide a termination
across T3 and to set the sample level.
T4 - Synthesizer Sync Sample
Ferrite inductor transformer T4 samples the current at the com-
biner output. The current sample goes to the Synthesizer Inter-
face board.
C7 - Network Voltage Sample
At the input of the Bandpass Filter, an RF voltage sample is
coupled by 3 capacitors and compared to the RF current sample
at the ground end of the combiner pipe.
4-10 888-2339-002 12/16/03
WARNING: Disconnect primary power prior to servicing.