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PAMS Technical Documentation
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For easy error tracing it is important to know the signal path of the GSM1800 receiver. The components
can be grouped into blocks and drawn as shown below.
SAW
LNA
SAW
RX
PCN
TX
LNA
RX
GSM
TX
Last edit 07:49 15.03.00
HDa12 RF Troubleshooting.doc
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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 GSM1800 signal is feed to the 1
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The GSM1800 front-end consists mainly of two SAW filters (Z501 and Z500) and one LNA (V500) in-
between and finally one balun (T500). 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 (C510,
L505 and C525) and to the GSM1800 LNA (V500, RFin).
The LNA has about 17dB gain when it is "on" (LNAB_G = 2.8V and LNA_P = 0V). If the signal applied
to the antenna-connector is more than –45dBm the AGC will gain-step the LNA (LNAB_G = 2.8V and
LNA_P = 0V) which means the LNA Gain will now have negative gain (loss) of –8dB.
From the LNA (V500 RF out) the signal is lead through the LNA-output-matching-circuit (C519),
nd
through the 2
Dual RX SAW Z500 (In-band insertion-loss 3,5dB) to the GSM1800 balun T500. From
the balun the signal is balanced and is lead to Hagar (N500 IMP_P_RX and INM_P_RX).
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The GSM1800 front-end consists mainly of two SAW filters (Z501 and Z500) and one LNA (V500) in-
between and finally one balun (T500). 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)
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Hagar
INP_P_RX
INM_P_RX
INP_G_RX
INM_G_RX
2
2
2
2
LNA_P /
LNAB_G
2
2
RF
LNA_G /
Controls
LNAB_D
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BIQUAD
BB_Gain
DtoS
8 / 18 dB
BIQUAD
BB_Gain
DtoS
8 / 18 dB
st
Dual RX SAW filter via C547.
NHM-2/5nx,ny/6/9
Troubleshooting
RXI
DNC2
0-40dB
VREF_RX
RXQ
DNC2
0-40dB
3DJH
VRF_RX
VREF
RXI
VREF_RX
RXQ
VCP
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