Operation Manual

SiteNet 450 Operation Manual 49
Using Radios with GPS B
Some communication transmitters and receivers also emit spurious
signals. These are extremely difficult to predict. The only way to know
if your receiver is being effected by spuriously emitted signals is to
test the communication equipment with the GPS receiver. If you plan
to buy a new radio, test it with your existing GPS equipment to
determine if any problems exist.
Communications equipment that uses more power is more likely to
create signals from which the GPS signal cannot be extracted. This
typically occurs from signals emitted from the radio transmitter box
and not its antenna. Non-GPS signals enter the GPS system through
the GPS antenna and not through the receiver. Therefore, most of the
effects of non-GPS signals can be minimized by physically separating
your radio and GPS equipment.
B.3 Useful Field Procedures
There are a few useful field procedures you can follow to minimize
the effects of your radio. Since most of the radio signal in the GPS
band is emitted directly from the radio transmitter box and received
via the GPS antenna, make sure the GPS antenna is separated from the
radio transmitter by 2-3 meters (7-10 feet). If you are still
experiencing difficulties at this distance, the GPS signal may be
getting overpowered by the radio transmissions. In this case, you can
either separate the equipment even more or shield the radio
transmitter.
As you move farther away from the source of the transmission, radio
signal strength drops as a square of the distance. Therefore, if there is
a problem, separate the GPS antenna and radio even more to lessen the
strength of the radio signal received at the GPS antenna.
If you are using a geodetic antenna, you can use the antenna’s ground
plane to shield the radio waves. In fact, you can shield the antenna
from the radio signal by moving behind nearby objects such as a car or
tree. If you cannot move away from the GPS antenna, move the radio
below the level of the GPS antenna ground plane. This is not ideal, but
may help in those cases where you are left with no alternative.
SN450.book Page 49 Friday, October 5, 2001 5:01 PM