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Message size
Table 5.4 lists the message size for RTCM messages 18 and 19.
7 GPS + 7 GLONASS
9 GPS + 9 GLONASS
12 GPS + 12 GLONASS
Required Radio Rate
For RS232 communications, 1 start bit and 1 stop bit is required for each byte. The
required number of bits is 10/8 times the number of message bits.
For RTCM, the data is packed in 6/8 format. The required number of bits is 8/6 times
the number of bits in the message.
For RTCM data on an RS232 link, the required number of bits is 8/6*10/8 times the
number of bits in the message.
Table 5.5 lists the minimum baud rates, for a GG-RTK receiver sending RTCM 18
and 19 messages only.
Number of Satellites
12 total GPS+GLO
14 total GPS+GLO
18 total GPS+GLO
24 total GPS+GLO
Table 5.5 lists the minimum baud rates, assuming no other data is sent on the data link. If other
RTCM messages are transmitted, then the minimum standard baud rate may increase.
The recommended optimal setting is to transmit type 18 and 19 messages once every
second on a high-speed link.
If a high speed data link is not available, you have indirect control over the number of
satellites used, by setting elevation mask angles. The elevation angle for any
particular satellite changes by 1° for every 100 km of baseline length. For baselines of
50
Table 5.4: Message Size for RTCM Messages 18 and 19
Number of RTCM Words in
Number of Satellites
Table 5.5: Minimum Baud Rates for RTCM Messages 18 and 19
Minimum baud rate
(message period = T)
30*30*2*8/6*10/8*1/T
34*30*2*8/6*10/8*1/T
42*30*2*8/6*10/8*1/T
54*30*2*8/6*10/8*1/T
Message Type 18.
(30 bits/word)
(2+1+2*7)*2 = 34
(2+1+2*9)*2 = 42
(2+1+2*12)*2 = 54
Minimum standard
baud rate (T = 5 sec)
600 bps
1200 bps
1200 bps
1200 bps
GG Surveyor GPS+GLONASS Reference Manual
Number of RTCM Words
in Message Type 19.
(30 bits/word)
(2+1+2*7)*2 = 34
(2+1+2*9)*2 = 42
(2+1+2*12)*2 = 54
Minimum standard
baud rate (T = 1 sec)
4800 bps
4800 bps
4800 bps
9600 bps
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