Chapter 5 Antennas
Antenna Kits and Accessories
244
SSU-2000e Technical Reference
12713140-003-2 Revision E.01 – January 2007
Antenna Kits and Accessories
This section provides a list of antenna kits and accessories as well as descriptions
and associated part numbers.
Selecting the Proper Gain Antenna
When installing the GPS radio receiver, it is important to select the proper gain
antenna and coaxial cable that accounts for the insertion loss between the antenna
and the radio receiver to avoid under-driving or over-driving the radio receiver
antenna input. The gain required at 1575 MHz for a GPS radio receiver input is the
manufacturer’s specification for the radio receiver to acquire satellites, with some
level of signal degradation allowed.
L1 Antenna gains are usually specified as the minimum effective gain. Such
antenna gains can have 4.5 to 10 dB more signal strength at different satellite
azimuths and elevations, depending on their reception pattern. The GPS engine
requires a signal level at the antenna connector input of the chassis to be between
13.8 dB and 36.8 dB. This tolerance allows for the signal loss of the internal coaxial
cable and connectors. The optimal signal level at the radio receiver input is 25.3 dB.
All antenna kits include the GPS L1 antenna, mounting pipe, floor flange, transient
eliminator, pre-assembled coaxial cable (for antenna to transient eliminator), roll of
3M 2150 weatherproof tape, and a right angle adapter. All chassis, antennas,
transient eliminators, and in-line amplifiers have N-type connectors.
All antenna kits supplied use LMR-400, or equivalent, low-loss coaxial cable. Other
types of coaxial cable are available for GPS antenna applications; however, it is
imperative that you calculate the specific cable loss to ensure a signal level
between 13.8 dB and 36.8 dB at the antenna connector input. The L1 signal loss of
LMR-400 is 1.67 dB/meter. The L1 signal loss of a 90 V transient eliminator is
typically 0.25 dB.
GPS Antenna With a Low Noise Amplifier, 26, 40, 48, or 68 dB
Symmetricom offers three versions of GPS antennas with 26, 40, 48, or 68 dB
internal Low Noise Amplifier (LNA). These antennas, which are compatible with
most commercial GPS receivers, receive, amplify, and filter the L1 (1575.42 MHz)
signal from GPS satellites. The antenna is housed in a weatherproof package
suitable for permanent installation in an exposed location. For additional transient
eliminator protection requirements, you can install a 250B-90 Gas Tube transient
eliminator in series with the antenna coaxial cable.
The cable between the antenna and the SSU-2000e cable should be kept to the
shortest reasonable length. With the appropriate antenna (lised in
), inline
amplifier, and coaxial cable, the antenna functions properly up to 1000 ft (305 m)
from the radio receiver. The tables listed below provide information about the
antenna:
