Operation Manual

B Using Radios with GPS
50 SiteNet 450 Operation Manual
B.4 Summary
Using communications radios with GPS receivers requires some
special considerations. By striving to extract the utmost accuracy from
the GPS system, receiver designs have made greater use of the radio
spectrum. However, the methods used to increase performance and
accuracy also make GPS receivers more susceptible to receiving other
radio signals.
Radio signals in the GPS band arise from a few different sources.
Some radio transmitters produce overtones of their frequency, which
lie within the GPS P-code frequency range. Others create random,
spurious signals, which affect GPS signal reception. Still other radio
systems use high power levels to boost communication range and
create noise that limits the GPS signal tracking. These are all
characteristics to avoid when purchasing or using communications
equipment in conjunction with GPS.
Before using radios on a full-fledged survey job, it is a good idea to
test the communications equipment to determine if it effects the GPS
signal reception in any way. Testing radios with the GPS equipment is
especially important if you are considering purchasing new radios.
Make sure to always:
• choose the communication frequency of your radios carefully
so they do not transmit on or create harmonics in the frequency
range of GPS.
• test them with your GPS receivers.
• if problems arise, put some distance between the radio
transmitter case and the GPS antenna. Also, shielding the radio
transmitter should minimize the effects of radio signals on the
GPS signal reception.
Radio signal strength drops as a function of distance. The greater the
separation between the GPS antenna and the radio transmitter, the less
likely you are to experience interruptions in satellite tracking.
SN450.book Page 50 Friday, October 5, 2001 5:01 PM