User Manual

Preinstallation RF-Orchestra!™ Transmitter Installation and Operation
3-14 6880493G02-C July 2000
Adjacent structures, such as trees or buildings, could obstruct signals. The GPS antenna must
be mounted clear of all obstructions to provide a clear path. Other adjacent antenna towers at
the RF site that protrude into the required view have a minimal effect on GPS satellite
reception and are not considered obstructions.
The GPS receiver can be jammed by high power carriers in the communications bands. This
symptom is the failure of the GPS receiver to track satellites. The minimum recommended
separation distance from any paging station antenna should provide at least 38 dB of path loss
from a 1-watt isotropic radiator. If in doubt, use at least 12 feet of horizontal separation
distance. Long runs of single-braid, shielded cable along with other radio cables can be subject
to jamming interference pickup. Motorola recommends solid copper outer conductor, coaxial
cable between the GPS antenna and receiver.
The RF connection of the Motorola internal GPS receiver provides +5 Vdc power to the GPS
antenna. The output is not reverse polarity protected. To run multiple receivers off one
antenna, choose one receiver to supply the +5 Vdc to the antenna. Place DC blocks in all other
branches to the GPS receivers.
The coaxial cable used to connect the GPS antenna to the GPS input on the Motorola internal
GPS receiver must be designed to satisfy the system gain requirements for the GPS receiver at
a frequency of 1575.42 MHz. The standard maximum cable loss allowed between the GPS
antenna and the RF-O! paging station is 6 dB. The standard maximum cable loss is included in
a system gain budget with additional items, such as line-of-sight loss and minimum satellite
power during satellite acquisition. The total line-of-sight loss (7 dB) includes foliage loss (for
example; low density tree tops, 6 dB) and ice loss (1 dB). The foliage loss could be reduced for
two other design considerations where foliage is not an issue (such as the top of a building).
The cable loss in the clear view case could be increased from the standard loss to 13 dB
(standard max cable loss plus line-of-site losses). Any additional trade-off is not
recommended because of the reduced signal margin during satellite acquisition. Alternatively,
the 6 dB for foliage loss could be used to account for an increase of the RF noise floor level
from nearby (in frequency) paging station noise floor additions. The cable system between the
GPS antenna and the Motorola internal GPS receiver should have a noise figure of less than
15 dB. The total system noise figure is not to exceed 4 dB.
CAUTION
The Motorola internal GPS receiver sources +5 Vdc power to the antenna using the
coax center pin.