E.F. Johnson Company ATLAS 4500, Техническое руководство

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A-2
ATLAS 4500 Multimode Station Technical Manual
May 2017
135-175 MHz Exciter Module Appendix A - VHF Circuit Descriptions
A.1.1 General Description
The Exciter module generates the low level RF transmitter signal that is amplified
to nominal output power level by the Power Amplifier. The exciter module consists
of two circuit boards. A Voltage Controlled Oscillator (VCO) board and a main RF
board with associated frequency synthesizers, a modulation controller, filtering/
amp circuits, DPD loop section below the board and internal power supply circuits.
Output frequency programming is achieved by using serial data connections to an
external controller.
If an external frequency reference is desired, the exciter can be fed with an external
10 MHz signal, otherwise it has an internal 10 MHz reference oscillator.
A.1.2 Schematic Description
A.1.2.1 Frequency Synthesizers
There are 4 synthesizers in the MDR Exciter: The main synthesizer, and 3
synthesizers used in the DPD error loop section.
The Synthesizer O/P from the VCO board on SKU-1 is split to the fractional-N
synthesiser IC6 main divider input and the error loop 1st mixer LO amp IC16.
This signal is compared with the 10 MHz reference oscillator frequency and the
correction voltage from the synthesiser’s charge pump output is filtered then
amplified by the non-inverting low noise op amp IC10. This correction voltage is
fed back to the VCO to maintain loop lock as well as being fed to the Controller
through TX VCO VOLTS CN3-14. A lock detect signal from IC6 is also fed to the
Controller through TX LD CN3-16. The op amp IC10 uses a 25 V power supply
generated by IC4 so as to provide a wide tuning range voltage to frequency control
varicap diodes located on the VCO board. Due to the wide VCO range used
different PLL charge pump values are set across the tuning range by the Controller.
The VCOs power is supplied by a dynamic filter TR6 and 8 V regulator IC11.
Frequency programming data for the exciter is sent to Synthesizer IC6 from the
Controller through serial data (CN3-18) under the control of the Clock (CN3-15)
and Strobe (CN3-17) lines.
Synthesizer IC28 and associated components provide a reference of 345.6 MHz for
IC31 DDS IC. This 345.6 MHz signal is frequency locked to the 10 MHz main
reference clock. The 345.6 MHz clock is divided by 8 within IC31 and outputs a
43.2 MHz clock that drives IC32 FPGA.