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User Manual
Airbridge cBTS3612 CDMA Base Station
Polarity: RHCP
GPS/GLONASS dual-satellite receiving antenna
l
This antenna receives L1 GPS signals (1.575GHz) and GLONASS signals
(1.611GHz). The power voltage is 5~18V.
III. Feeder
The feeder is the physically foamed polyethylene insulation RF coaxial cable, with
the impedance of 50-ohm and specification of 10-FB. Nominal indices are:
70dB/km (400MHz)
113dB/km (900MHz)
The loss at 1.575GHz frequency is 13.78dB every 100m.
The coaxial cable is mainly used to transmit the GPS signals received by the GSP
antenna to GPS card. At the same time, the coaxial cable also provides power for
the antenna module to make pre-amplification.
This kind of cable is used when dual-satellite solution is adopted.
IV. Lightning arrester of antenna and feeder
The lightning arrester of antenna and feeder used in BTS features clamp voltage of
-1~+7VDC, standing wave ratio of less than 1.1:1, and signal attenuation of less
than 0.1dB (1.2~2GHz ).
V. Receiver
GPS receiver has 8 parallel paths, capable of tracking 8 satellites concurrently. The
receiver receives GPS signal of band L1 (1575.42MHz) and tracks C/A code. The
receiver must be powered with regulated 5V DC. Inside the receiver, the RF signal
processor makes frequency down-conversion to the GPS signal received by the
antenna to get Intermediate Frequency (IF) signal. The IF signal is then converted to
digital signal and sent to 8-path code and carrier correlator, where signal detection,
code correlation, carrier tracking and filtering are performed. The processed signal
is synchronized and sent to positioning MPU. This part of circuit controls the
operational mode and decoding of GPS receiver, processes satellite data, measures
pseudo-distance and pseudo-distance increment so as to figure out the position,
speed and time. The sensitivity of the receive card is -137dBm.
The dual-satellite receive card has 20 receiving paths. GPS L1 can be upgraded to
GPS/GLONASS L1+L2 or other solutions. The timing accuracy of the card is up to
25ns.
2-49
System Description
2 Hardware Architecture
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