Technical Manual

380-520 MHz Receiver Module
Appendix A - UHF Circuit Descriptions
A-8
ATLAS 4500 Multimode Station Technical Manual July 2021
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 (which 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 approximately -53 dBm for -100 dBm RX I/P and
approximately -13 dBm for -60 dB RX I/P at 800MHz)
A.2.2.6 Receiver DC Supplies
The exciter is supplied nominal 13.8 V through SK1-2. This input supply is then
distributed to IC1 and IC4.
IC1 is configured as a buck DC-DC converter and provides a regulated +5.2 VDC
output.
IC4 is configured as a boost DC-DC converter and provides +25 V DC output.
IC3 regulates +5.2 V supply down to +5 VDC.