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MiLLennium GPSCard SW Version 4.503/4.52 Command Descriptions Manual Rev 2 19
Generally, a communications link capable of data throughput at a rate of 4800 bits per second or higher is
sufficient. However, it is possible to satisfactorily use a lower rate (e.g. 2400 bps) with the RTCA, RTCM59 and
CMR formats. RTCM Types 18 and 19 may require a higher rate; see Chapter 4, Message Formats, Page 46 for
additional information. The minimum data transfer rate is based on the following:
1. RT-2 requires that the reference station periodically transmit two RTCA Standard Type 7 messages:
• An RTCAOBS message contains reference station satellite observation information, and
should be sent once every 1 or 2 seconds.
• An RTCAREF message contains reference station position information, and should be
sent once every 10 seconds.
OR periodically transmit an RTCM Type 18 and RTCM Type 19 (RTCM1819) message together with an
RTCM Type 3 message:
• A Type 3 message contains reference station position information, and should be sent
once every 10 seconds (although it is possible to send it as infrequently as once every 30
seconds).
• RTCM1819 gives raw measurement information (Type 18 provides carrier phase
measurements, while Type 19 provides pseudorange measurements) and should be sent
once every 1 or 2 seconds.
NOTE: This message can be sent in RTCM Version 2.1 or Version 2.2 format, controlled with the RTKMODE
command.
and, optionally, also periodically transmit an RTCM Type 22 message together with an RTCM Type 3
message:
• A Type 3 message contains reference station position information, and should be sent
once every 10 seconds (although it is possible to send it as infrequently as once every 30
seconds).
• A Type 22 message gives extended reference station parameters and should be sent once
every 10 seconds.
OR periodically transmit two CMR messages where the station ID, see Page 100, must be
≤ 31 when
transmitting CMR corrections:
• A CMROBS message contains reference station satellite observation information, and
should be sent once every 1 or 2 seconds.
• A CMRREF message contains reference station position information, and should be sent
once every 10 seconds.
2. RT-20 requires that the reference station periodically transmit either the RTCA messages listed above (the
recommended option), or RTCM 1819 or CMR messages or the RTCM SC-104 Type 3 & 59N messages:
• A Type 3 message contains reference station position information, and should be sent
once every 10 seconds (although it is possible to send it as infrequently as once every 30
seconds).
• A Type 59N message contains reference station satellite observation information, and
should be sent once every 2 seconds.
Further information on RTCA, RTCM and CMR message formats is contained in Chapter 6.
System Initialization
The RTK system is designed for ease of use: you set up the remote station, enter a command so that it accepts RT-
2 or RT-20 messages from the reference station, and are ready to go. There are options, however, which can be
used to adapt the system to a specific application. Some options apply only to the reference station, while others