User Guide

PAMS
Technical Documentation
RAE-3
8. Troubleshooting
Page 8 – 117
Issue 1 06/01
5.2.1 PCN Signal Path
For easy error tracing it is important to know the signal path of the PCN receiv-
er. The components can be grouped into blocks and drawn as shown below.
2
2
2
2
INP_P_RX
INM_P_RX
RX/TX Switch
RX
RX
TX
TX
INP_G_RX
INM_G_RX
DNC2
DNC2
LNA_P
RXQ
RXI
OUT_BB1_I OUT_BB1_Q I_DCN2_I I_DCN2_Q C1_BB1_I C2_BB1_I C2_BB1_Q C1_BB1_Q Cp_f_I Cm_f_I Cp_f_Q Cm_f_Q Cp_dtos_I Cm_dtos_I Cp_dtos_Q Cm_dtos_Q
0–40dB
BB_Gain
0–40dB
BB_Gain
DtoS
DtoS
BIQUAD
BIQUAD
GSM
PCN
VRF_RX
VREF_RX
VB_EXT RB_EXT
RF
Controls
LNA_G
8 / 18 dB
8 / 18 dB
SAW
SAW
SAW
SAW
LNA
LNA
Hagar
VRF_RX
VREF_RX
VREF
RXI
RXQ
LNAB_G
Antenna connector
Figure 122. PCN RX signal path
5.2.2 RX/TX Switch
From the internal antenna connector (X499) the RF signal is lead to the RX/TX
switch (Z670) via a mechanical switch, the antenna connector (X900).
The RX/TX switch is normally open to the two RX outlets GSM_Rx and
DCS_Rx. If no control voltage is present at VC1 or VC2 the RX/TX switch will
work as a diplexer and PCN signals pass to DCS_Rx and EGSM signals to
GSM_Rx.
From DCS_Rx the PCN signal is feed to the 1
st
PCN SAW filter via C645.
5.2.3 Front end
The PCN front–end consists mainly of two SAW filters (Z620 and Z600) and
one discrete LNA (V903) in–between and finally one balun (T630). The SAW
filters provides out–of–band blocking immunity, the LNA provides front–end
gain and the balun provides a balanced signal for Hagar (N505)
The signal–path is Through Z620 (In–band insertion–loss max 4dB), through
the matching circuit (C674, C644, L647) and to the PCN LNA (V903, RFin).
The LNA has about 18 dB gain when it is on (LNA_P = 2.8V and Vlna=2.8V). If
the signal applied to the antenna–connector is more than –45dBm the AGC will
gainstep the LNA (LNA_P = 0V) which means the LNA Gain will now have
negative gain (loss).
From the LNA transistor collector (V904 RF out) the signal is lead through the
LNA–output–matching–circuit (R640, L633, C640, L646), through the 2
nd
PCN
SAW Z600 (In–band insertion–loss max 4dB) through a matching–network
(C720 and L706) and to the PCN balun T630. From the balun the signal is bal-
anced and is lead to Hagar (N505 IMP_PCN_RX and INM_PCN_RX).
5.2.4 Hagar
The balanced RX signal is mixed with a signal from the local oscillator at the
same frequency as the wanted RX signal. After mixing the signal is converted