PAMS Technical Documentation
Troubleshooting
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For easy error tracing it is important to know the signal path of the EGSM receiver. The components
can be grouped into blocks and drawn as shown below.
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From the antenna-pad the RF signal is lead to the RX/TX switch (Z502).
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 the EGSM signal is pass to
GSM_Rx and the GSM1800 signal to DCS_Rx.
From GSM_Rx the EGSM signal is feed to the 1
st
Dual RX SAW filter via C556.
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The EGSM front-end consists mainly of two SAW filters (Z501 and Z500) and one LNA (V501) in-
between and finally one balun (T501). The SAW filters provides out-of-band blocking immunity, the
LNA provides front-end gain and the balun provides a balanced signal for Hagar (N500)
The signal-path is through Z501 (In-band insertion-loss 3,5dB), through the matching circuit (C545,
L507 and C541) and to the EGSM LNA (V501, RFin).
The LNA has about 18dB gain when it is "on" (LNA_G = 2.8V and LNAB_D = 2.8V). If the signal
applied to the antenna-connector is more than –45dBm the AGC will gain-step the LNA (LNA_G = 2.8V
and LNAB_D = 0V) which means the LNA Gain will now have negative gain (loss) of –12 dB.
From the LNA (V501 RF out) the signal is lead through the LNA-output-matching-circuit (C537, L520
and C534), through the 2
nd
Dual RX SAW Z500 (In-band insertion-loss 3,5dB) to the EGSM balun
T501. From the balun the signal is balanced and is lead to Hagar (N500 IMP_G_RX and INM_G_RX).
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Last edit 07:49 15.03.00
HDa12 RF Troubleshooting.doc
0-40dB
BB_Gain
0-40dB
BB_Gain
DtoS
DtoS
BIQUAD
BIQUAD
GSM
PCN
VR
F
_
R
X
VREF_RX
VB_EXT
R
B
_EXT
RF
Controls
LNA_G /
LNAB_D
8 / 18 dB
8 / 18 dB
SAW
SAW
LNA
LNA
Hagar
VRF_RX
VREF_RX
VREF
RXI
RXQ
VCP
2
2
