Hemisphere GPS MBX-4, User Manual

Page: 16 / 94

MBX-4 User Guide
7
Radiobeacon Reception
Various sources of noise affect beacon reception, and include:
• Engine noise
• Alternator noise
• Noise from Power lines
• DC to AC inverting equipment
• Electric devices such as CRT’s electric motors, and solenoids
Noise generated by this type of equipment can mask the beacon signal,
reducing or impairing reception. The “Antenna Placement to Optimize
Reception” section on page 24 presents an effective procedure to
minimize impact of local noise on beacon reception when using this
correction service.
Radiobeacon DGPS
Radiobeacons conforming to the standards of the International
Association of Lighthouse Authorities broadcast a limited selection of
RTCM SC-104 messages, including message types 1, 2, 3, 5, 6, 7, 9, and
16.
• A DGPS beacon will broadcast either Type 1 or Type 9
messages, both of which contain similar information. These
two messages contain pseudorange corrections and range rate
corrections to each GPS satellite.
• The Type 2 message contains delta differential corrections that
are used when the remote receiver is using a different satellite
navigation message than used by the base station.
• The Type 3 message contains the position of the beacon’s
reference station, often accurate to within centimeters with
respect to the WGS-84 reference datum.