User's Manual

RTC to complete the control loop that provides the proper power level and pulse shape. The RTC
compares this detected signal to the desired output pulse shape, calculates the necessary corrections, and
pre-distorts the shaped pulse control signals used by the High Power Amplifier module.
1.3.2.12.2 Power Supply CCA Block Diagram Theory
The Power Supply CCA within the High Power Amplifier assembly contains two of the same DC/DC
converters used on the Low Power Amplifier Module running in parallel with the input voltages range of
36VDC to 60VDC. The nominal output voltage is 53.7VDC set by the Master converter with the second
converter set as a Slave to share the load current. This nominal voltage is passed to the Modulator CCA
(012178) for modulation and power control of the RF transistors. This nominal output voltage is also
DC/DC converted to 12VDC using a switching regulator. The other required DC voltages used within the
module are linear regulated from the 12VDC voltage. The DC/DC converter and switching regulator
voltages are monitored for proper DC levels using a window comparator. This signal is sent to the RTC for
“bite” monitoring with a logic level “0” indicating a “POWER GOOD” condition. A front panel status LED
is provided, and is illuminated green to indicate this “power good” condition. The transmitter’s energy
storage capacitors are contained on this circuit assembly.
1.3.2.12.3 RF Amplifier / Transmitter Assembly Theory
The transmitter portion of the HPA Module provides amplification of the RF signal and is comprised of
three assemblies. The first assembly contains an attenuator pad, and one amplification stage for HP DME
configuration or two amplification stages for TACAN use. The second assembly is comprised of four
transistors in parallel. The last assembly board contains a low pass filter and a coupler. The transistors on
the first assembly board all “square wave” modulated while the final transistors in parallel are “Gaussian
pulsed” modulated regardless of High Power DME or TACAN configuration. All transistors are bi-polar
junction transistors (BJT) and are operated in Class-C mode, common base. This module is capable of
transmitting in excess of 1000W peak at the output port of the module in order to insure 1000 watt output
power at the antenna connector at the top of the system cabinet. The transmitter is described in the
following paragraphs.
1.3.2.12.4 HP Driver CCA Block Diagram Theory
Refer to Figure 1-18. The input to the driver board receives a “square wave” input signal from the low
power module. The signal is attenuated and then amplified by one or two stages depending upon
configuration. The attenuator pad serves two purposes. The first is that it prevents the amplifier from
being over-driven by the low power module, and the second is that it maintains impedance stability
between modules. Depending upon the configuration, the “square wave” signal is then amplified by one
stage in the DME configuration or by two stages in the TACAN configuration. The voltage supplies of the
transistors are “square wave” modulated in synchronization with the Low Power Module. The pulse width,
gain, and output signal level are controlled by its own modulator.
NOTE: The printed circuit board used is the same for both DME and TACAN; parts are simply added or
removed during assembly of the DME and TACAN versions of the high power amplifier.
1.3.2.12.5 HP Final CCA Block Diagram Theory
Refer to Figure 1-18. The final driver receives the “square wave” input signal and splits the signal into four
transistors using multi-stages of 3dB hybrid couplers. At this point, the signal is amplified and converted
into a “Gaussian pulse” by modulating the transistor’s voltage supplies. The hybrid couplers provide
sufficient isolation among the four transistors and the driver to avoid instability when transforming the
signal. The proper pulse shaping and output signal level is controlled by its own modulator circuit. The
signals are recombined using multi-stage hybrid couplers. Once again the couplers provide adequate
isolation among the transistors in case of a transistor malfunction or voltage standing waves.
1.3.2.12.6 HP Output CCA Block Diagram Theory
Refer to Figure 1-18. The Output CCA contains a low pass filter and a coupler. The low pass filter is
designed for minimal insertion loss through the transmitter band and provides a nominal 40dB of
attenuation for unwanted high frequency spurious signals. The filter is shielded and uses both printed