DOC 6501_Release V
ATS-6501 Users Guide
10
WARNING:
An outside antenna system should not be located in the vicinity of
overhead power lines or other electric light or power circuits, or where it can fall into
such power lines or circuits. When installing an outside antenna system, extreme care
should be taken to keep from touching such power lines or circuits as contact with them
might be fatal.
Figure 1
Antenna Location
C.
Once a suitable antenna location has been identified, it is necessary to ensure that the
GPS signal that reaches the ATS-6501 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 ATS-6501 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 ATS-6501.
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.