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Old 15-05-2011, 23:14   #1
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rmb, rmc with Geonav 4c and Furuno


I have a setup aboard that can handle two gps's: a Geonav 4c and a Furuno GP31. I choose either one of them to be in operation. To show the information, there is a Clipper GPS repeater. As soon as I put in a waypoint in the Furuno, the clipper show COG, SOG, DTW and Bearing. As soon as I do the same on the Geonav (Furuno switched off), the same information is shown, however the display of the clipper is blinking. Having a look at the NMEA 0183 data, I notice some differences:

$FRRMC = Furuno
$ECRMC = Geonav 4c

$FRRMC,132010,A,5142.4439,N,00405.0567,E,0.0,170,1 50511,1,W*6D

$ECRMC,131842,A,5142.447,N,00405.056,E,000.0,000.0 ,,000.1,W,A*13

RMC - NMEA has its own version of essential gps pvt (position, velocity, time) data. It is called RMC, The Recommended Minimum, which will look similar to:
$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4 ,230394,003.1,W*6A

RMC Recommended Minimum sentence C
123519 Fix taken at 12:35:19 UTC
A Status A=active or V=Void.
4807.038,N Latitude 48 deg 07.038' N
01131.000,E Longitude 11 deg 31.000' E
022.4 Speed over the ground in knots
084.4 Track angle in degrees True
230394 Date - 23rd of March 1994
003.1,W Magnetic Variation
*6A The checksum data, always begins with *
Note that, as of the 2.3 release of NMEA, there is a new field in the RMC sentence at the end just prior to the checksum. For more information on this field see here.
Regarding RMB:
$ECRMB,A,0.00,R,0000,0001,5142.445,N,00405.366,E,0 00.19,090.6,,V,A*49

$FRRMB,A,0.00,L,START ,LWST11,5130.870,N,00400.286,E,12.0,194,0.0,V*68
RMB,A,0.66,L,003,004,4917.24,N,12309.57,W,001.3,05 2.5,000.5,V*0B
A Data status A = OK, V = warning
0.66,L Cross-track error (nautical miles, 9.9 max.),
steer Left to correct (or R = right)
003 Origin waypoint ID
004 Destination waypoint ID
4917.24,N Destination waypoint latitude 49 deg. 17.24 min. N
12309.57,W Destination waypoint longitude 123 deg. 09.57 min. W
001.3 Range to destination, nautical mil
052.5 True bearing to destination
000.5 Velocity towards destination, knots
V Arrival alarm A = arrived, V = not arrived
*0B mandatory checksum
It's noticeable that there is no velocity towards destination (,,) and a contrary arrival alarm.

I also noticed that GGA has is missing a date.

Enclosed two nmea-data files.

Anyone who has the same experience or is willing to help me to sort this out?

Thanks in advance!
George64 is offline   Reply With Quote


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