LG PX8700 Service Manual page 29

PX8700
1.2 Description of RX Part Circuit
1.2.1 Triplexer Filter (U104)
The main function of Triplexer is to prohibit the other band signals from flowing into the one
band circuit and vice versa. RF designer can use common tri-band antenna regardless of
frequency band (800, 1575 and 1900 MHz). The specification of PX8700 Triplexer is described
below:
Frequency Range
Insertion Loss to
Common
Isolation
Temperature Range
1.2.2 Duplexer (DP104, DP101)
The duplexer consists of the RX bandpass filter (BPF) and the TX BPF which has the function of
separating TX and RX signals in the full duplex system for using the common antenna. The TX
part BPF is used to suppress noises and spurious out of the TX frequency band. The RX BPF is
used to receive only RX signal coming from the antenna, which is usually called preselector.
It' s main function is to limit the bandwidth of spectrum reaching the LNA and mixer, attenuate
receiver spurious response and suppress local oscillator energy. As a result frequency
sensitivity and selectivity of mobile phone increase. The specification of PX8700 duplexer
described below ;
PCS duplexer:
Pass Band 1850~1910 MHz
Insertion Loss
Return Loss
Attenuation
(1930~1990MHz)
LG Electronics Inc.
Cellular
824 – 894 MHz
1.0 dB Max
(At +25 deg)
48.5dB
(Cell TX)
TX
3.5dB max
8.0dB min
40dB min
GPS
1575.42 MHz
1.8 dB Max.
(At +25 deg)
32.9dB(GPS-Cell)
18.3(GPS-PCS)
-30 to +85 deg
RX
1930~1990 MHz
3.0dB max
8.0dB min
50dB min
(1850~1910MHz)
PCS
1850 – 1990 MHz
0.85 dB Max
(At +25 deg)
53.1dB
(PCS TX)
TX to RX (min)
54dB (1850~1910MHz)
44dB (1930~1990MHz)
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