E.F. Johnson Company ATLAS 4500, Техническое руководство

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A-8
ATLAS 4500 Multimode Station Technical Manual
May 2017
135-175 MHz Receiver Module Appendix A - VHF Circuit Descriptions
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 synthesiser 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. 2
frequency bands are used. 135 – 155 MHz and 155 – 175 MHz.
The 4 band pass filter switches use 4 lines (SK1 – 19), (SK1 – 20), (SK1 – 21),
(SK1 – 22)
A.2.2.5 55 MHz IF Section
A VCO signal generated by the synthesiser is fed into a RF mixer (X8) where it
produces a fixed frequency output of 55 MHz. This IF output is then fed through an
input matching network through a 2 pole crystal filter (FL7) and associated output
matching network and is then amplified further by IC49 and associated
components. Limiting is provided for overload.
The IF signal is filtered further by a 4 pole crystal filter FL8A and FL8B and their
matching networks before being amplified further by TR8 and associated
components. The 55 MHz IF output is fed for external signal processing in the DSP
RX board through connector CN2.
(The 55 MHz IF O/P level is ~ -53 dBm for -100 dBm RX I/P and ~ -13 dBm for -
60 dB RX I/P at 155 MHz)
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 reg5.2 VDC
output.