Technical Manual

A-8 ATLAS 4500 Multimode Station Technical Manual July 2016
792-825 MHz Receiver Module Appendix A - 700/800 MHz Circuit Descriptions
Each band is switched under control of the Controller. 2 MMIC buffers feed the
synthesizer and main outputs. The power supply to the VCO consists of an 8-V
regulator and active filter for maximum noise rejection located on the exciter PCB.
The 8-V supply consists of IC11, TR6 and associated components.
The PLL control line varies VCO frequency (SKT – 1).
A.2.2.3 Reference Clock
A stable 10 MHz reference is generated by X1—a temperature controlled crystal
oscillator (TCXO), and fed to the synthesizer IC6 through an amplifier consisting
of TR2 and associated components.
A.2.2.4 Front End
The incoming signal from the antenna is connected to CN1, where it passes through
a low pass filter then a limiter before amplification by IC2 (this can be linked out
for higher dynamic range). After IC2 the signal is fed to a band pass filter network
switched by IC19 and IC26. From here, the signal is amplified by IC34 and fed into
another band pass filter network with the band in use switched by IC18 and IC20.
ICs 18, 19 20 & 26 are controlled from the external Controller through 4 digital
logic signals that select the correct filters for the frequency sub-band in use.
The 4 band pass filter switches use 4 lines (SK1 – 19), (SK1 – 20), (SK1 – 21),
(SK1 – 22)
A.2.2.5 90 MHz IF Section
A VCO signal generated by the synthesizer is fed into a RF mixer (X8) where it
produces a fixed frequency output of 90 MHz. This IF output is then fed through an
input matching network through a crystal filter (FL7) and associated output
matching network and is then amplified further by IC49 and associated
components. The IF signal is filtered further by crystal filters FL8A and FL8B and
their matching networks before being amplified further by TR8 and associated
components. The 90 MHz filtered IF output is fed for external signal processing in
the DSP RX board through connector CN2.
(The 90 MHz IF O/P level is ~ -53 dBm for -100 dBm RX I/P and ~ -13 dBm for -
60 dB RX I/P at 800MHz)