DOC 4380A
4380A O & M Manual
8
098-00723-000
– Jul 2017 Revision 4.0
SyncSystem 4380A O&M Manual
Un système extérieur d'antenne ne devrait pas être situé à proximité des lignes à haute tension
aériennes ou d'autres circuits de lumière électrique ou de puissance, ou où il peut tomber dans de
tels lignes à haute tension ou circuits. En installant un système extérieur d'antenne, le soin
extrême devrait être pris pour le garder de toucher de tels lignes à haute tension ou circuits comme
entrent en contact avec eux force soyez mortel.
Poor Antenna Location
Better Antenna Location
Best Antenna Location
Figure 2 Antenna Location
C.
Once a suitable antenna location has been identified, it is necessary to ensure that the GPS signal
that reaches the 4380A is of suitable quality. The unit requires a minimum of 15dB gain from the
antenna gain combined with the amount of loss in the antenna cable. The antenna included with
the 4380A has 25dB of gain so the total cable losses in the system must not exceed 10 dB at 1.5
GHz. If you are using a different antenna please ensure the antenna gain combined with the cable
loss will provide sufficient signal strength for the 4380A.
D.
If the location of the antenna dictates that a longer cable must be used, then a line amplifier will
need to be inserted into the signal path or you will need to run an antenna cable with less loss. A
line amplifier is a device used to amplify the GPS signal to overcome the losses resulting from
longer cable runs. In selecting a line amplifier, it is necessary to make sure that it provides an
adequate amount of gain and that it operates from 1200MHz to 1600MHz.
E.
The amount of gain required from a line amplifier can be calculated by knowing the total loss of
the antenna cables being used. The signal loss due to a cable varies depending upon the frequency
of the signal. For the purposes of GPS antennas, the cable loss should be calculated at 1500MHz.
The manufacturer of the cable being used should be able to provide an estimate of the cable loss at
1500MHz. Once the cable loss is known, it can be inserted into Equation 2-1 to calculate the
required gain of the line amplifier.
12
100
)
(
_
*
)
100
/
(
_
)
(
_
ft
Length
Cable
ft
dB
Loss
Cable
dB
Gain
MIN
Eq. 2-1.
F.
The
MIN_Gain
value in Equation 2-1 serves as the minimum gain required from the line amplifier
being used. It is possible to use amplifiers with a slightly higher gain than the minimum value but
it will not improve the performance of the system. Using amplifiers with significantly higher gain
values can also cause degradation of the GPS signal because it overdrives the input of the GPS
receiver.
G.
Placement of the line amplifier is also a concern in a properly designed system. Placing the
amplifier too far from the antenna may cause unexpected degradation in the GPS signal and the
performance will remain poor. The best place for the amplifier is typically half way between the
antenna and the 4380A. This allows the line amplifier to benefit from any surge protection that
may be installed near the antenna, but is still close enough to the antenna so as not to degrade the
signal significantly. Figure 2 shows the block diagram of a typical installation that requires a
longer antenna cable. Another consideration when installing the line amplifier is how it will
receive power. Some amplifiers are powered using a DC bias on the antenna cable and others are
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