User's Manual
The Circulator provides isolation between the transmitted and received signals, since a common antenna is
used for both. Signals applied to any of the ports will experience the least insertion loss or minimum
resistance when traveling to the adjacent port in a clockwise direction. Signals traveling in a
counterclockwise direction will be attenuated by at least 20 dB. Aircraft interrogations and monitor
interrogations arriving from the Directional Coupler are directed to the Preselector Assembly by the
circulator.
The Preselector Assembly is a narrow-band, three-pole, mechanically-tuned filter that discriminates against
undesired frequencies and provides additional attenuation of transmitter energy. From the Preselector, the
received interrogations are directed to the receiver input of the Receiver Transmitter Controller (RTC) after
being amplified by the Low Noise Amplifier (LNA).
Within the receiver is a low-noise high stability local oscillator that is generated by an internal synthesizer.
This signal is mixed with the incoming RF to provide a 125 MHz first IF signal that is log detected and
digitally processed for accurate interrogation time of arrival. The 125MHz IF is further down converted to
a 10.7 MHz IF signal. This 10.7 MHz signal is narrow-band filtered and used to determine if the received
interrogation was on-channel or from an adjacent channel.
The Low Power Amplifier Module delivers 125 watts peak Gaussian shaped pulses at the output connector
when used in the Low Power DME. This translates to a minimum 100 W output at the antenna connector
of the station allowing for normal losses in the connecting cables, directional couplers, etc. The output
power is attainable on any DME channel from 960-MHz to 1215-MHz without requiring re-tuning of the
amplifier. The Low Power Amplifier module provides in nearly 200 watts shaped pulses when used as the
driver amplifier in either the 2170 High Power DME system, or the TACAN system.
The Low Power Amplifier Assembly consists of three major circuits: the transmitter RF synthesizer, the
Modulator and the RF Amplifier. The RF synthesizer is programmed via a serial interface to the station
transmit frequency. A sample of the CW output of the synthesizer is available on the front panel of the
Low Power Amplifier module to allow verification of transmitter frequency by external test equipment.
The CW output of the synthesizer is pulse modulated by an RF switch controlled by the gate pulses from
the RTC, then amplified to 26.5 dBm at the output of the synthesizer CCA within the Low Power Amplifier
module. The synthesizer assembly also contains a DC/DC converter to provide the high voltage (~51 volt)
supply used within the Low Power Amplifier module. This DC/DC converter will operate over an input
range in excess of 40 to 60 volts DC, providing a stable supply voltage for the RF amplifiers even when the
DME system is operating on batteries and is nearing the end of the useful battery life.
The pulse modulated RF signal is then routed through a 4-stage RF amplifier to achieve the final output
power of =200 watts peak. The Modulator CCA within the Low Power Amplifier assembly performs the
required pulse shape modulation and output power control. The Gaussian shape desired when used as a
stand-alone low power transmitter (2160 DME) is achieved by a linear modulator under control of the RTC
module within the DME system. Detected output pulses from the low power amplifier module are routed
to the RTC, where they are compared to the desired pulse shape, and pre-distorted Gaussian shaped control
pulses are sent from the RTC to the Low Power Amplifier assembly where they control the outputs of the
Modulator CCA. When the Low Power Amplifier module is used in either the 2170 High Power DME or
the TACAN, the output is amplitude controlled by the RTC, and the pulse shaping is done in the low-power
amplifier modulator.
The High Power Amplifier module (used only in the 2170 High Power DME and the TACAN, not shown
in Figure 2-4) consists of three major circuits, the Modulator and the RF amplifier, and the DC/DC
converter. There is a slight difference in the TACAN version of the High Power Amplifier RF Amplifier
and the DME version of the High Power Amplifier. In the TACAN version, there is an additional driver
amplifier stage to compensate for the reduction in input power because the output of the Low Power
Amplifier is split 5-ways. In the DME application, the full output of the Low Power amplifier is applied to
the input of the High Power amplifier, hence this additional stage is not needed. The DME version of the
High Power Amplifier has two gain stages, a 500 watt amplifier followed by a 4-wide 2000 watt peak