Mentor XL
12.4
GPS
A
NTENNA
–
I
NTERNAL
R
ECEIVER
When using the internal receiver, each Mentor XL fitted with the 360-15-12 GPS Module requires a
separate outdoor antenna with the following characteristics:
•
Active single antenna powered from the receiver module via the Mentor XL antenna
connector.
•
The 360-15-12 requires a 5 V dc antenna.
•
Reception frequency optimised for 1575.42 MHz
•
10 dB to 50 dB gain as measured at receiver input (antenna performance dictated by
antenna manufacturer). Antenna types with lower gain performance cannot support longer
cable runs: please see antenna and cable recommendations below.
•
Connection by co-axial cable terminated at the Mentor XL rear panel with
50Ω
BNC male
connector.
Magnetic patch antennae suitable for vehicle mounting will also be satisfactory but only with very
short cable runs (10 metres or less).
12.4.1
Recommended antenna type
•
Trimble Bullet III with TNC or F termination. 5 V dc.
This antenna provides a maximum gain of 38 dB when powered with 5 V dc. Trilogy can provide the
Trimble Bullet III, 5V model suitable for the 360-15-12 GPS module, complete with Universal Mount.
Order as Trilogy part no.
360-15-03.
Other antennae may be suitable: please check manufacturer’s specifications.
12.4.2
Cable considerations
Theoretically, 50Ω cable sho
uld be used to connect the GPS antenna. However, extensive testing by
Trimble, manufacturer of our recommended antenna, has shown negligible attenuation differences
between 50Ω and 75Ω cable types. In practice, it is far more important to select a cable with low
attenuation characteristics around 1.6 GHz.
Using the recommended antenna, the overall attenuation of the installed antenna cable run should
not exceed 20 dB. In addition to the attenuation specified by the cable supplier, a number of
additional factors can adversely influence the overall result:
•
Quality of terminations. Incorrectly terminated connectors can each contribute an additional
2 dB to the overall attenuation.
•
Multiple cables joined with barrels. Each join of this type can contribute an additional 3 dB
to the overall attenuation figure. Use a single, continuous cable.
•
Cable location. Do not allow the cable to rest in standing water: the water will gradually
permeate the cable jacket and degrade the signal. If a cable is run over a flat roof, suspend
the cable from suitable cable hangers.
•
At the point of connection to the antenna, arrange the cable to form a drip loop, to
eliminate water ingress.
Page 62 of 84
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