Thales NSS 100S-1 Component Maintenance Manual With Illustrated Parts List page 41

COMPONENT MAINTENANCE MANUAL
C17004
(2) RPU Operating Principle (see Figure 4)
(a) Reception of satellite signals
The GPS signals transmitted by several satellites are received by
the RPU (radio-frequency input RF), connected on HF PCB.
Each satellite transmits two waves, with carrier frequency:
L1 = 1575.42 MHz and L2 = 1227.60 MHz.
Each carrier frequency is modulated BPSK (Binary Phase Shift
Keying).
L1 frequency is modulated with C/A code (coarse acquisition code).
L1 and L2 frequencies are modulated by P code (precise acquisition
code).
Each satellite signal contains an identification code and navigation
data.
Two types of HF PCB can be mounted, which can process one or two
frequency waves (see versions chart).
The HF PCB also receives an signal OL generated by a local
oscillator, which is in turn controlled by a 10 MHz clock sent from
PCB Z5.
The intermediate frequency signal IF, available at the output of the
frequency converter, is applied to the IF amplifier; this amplifier
receives an AGC signal which is generated by the Asic circuit T100,
followed by a D/A converter.
The amplified IF signal is transformed into a digital signal by the
A/D converter before being processed digitally.
34-57-96
Page 19
OCT 15/01
© THALES AVIONICS
COPYRIGHT SEXTANT Avionique 1995
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