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Revision 1.8 Appendix D – Transmitting True Heading Data Page D1
®®
Appendix D – Configuring the SSC200 to Transmit True
Heading Data
The SSC200 is factory configured to transmit magnetic heading data on the NMEA0183 interface. Some NMEA
0183 applications require true heading data. This application note describes how to configure the SSC200 to
transmit true heading data
Prerequisites:
• The SSC200 compass must have firmware revision 1.7 or greater.
• The SSC200 compass must either transmit the default HDG sentence or be configured to transmit the
HDT sentence (see Application Note #1, “Configuring the SSC200 to Transmit the HDT Sentence for
Satellite Antennas and Radars”).
Instructions:
There are two choices for a magnetic variation source for the SSC200, GPS (preferred) or manual.
GPS Variation
In order to use a GPS to enable the SSC200 compass to transmit true heading data, the GPS antenna must
transmit magnetic variation data. Not all GPS antennas transmit magnetic variation data. Please consult the GPS
antenna user’s manual for details.
1. Ensure that the GPS antenna is configured to transmit either the RMC or VTG sentence. Either sentence
should work equally well.
2. Connect the NMEA 0183 output of the GPS antenna to the NMEA 0183 input of the SSC200. Please note
the following cable connections on the SSC200:
GPS Connection
SSC200 Connection
TXA (TX+) Blue Wire, RXA (RX+)
TXB (TX-) White wire, RXB (RX-)
3. The SSC200 should now be transmitting true heading data. Examine the NMEA 0183 sentences coming
from the SSC200 or check the heading indication on the system connected to the NMEA 0183 output of
the SSC200 for true heading data.
4. If no true heading data is observed at this point, try
d. switching the wires on the GPS->SSC200 connection, as not all manufacturers are consistent in
their labeling of the NMEA 0183 wires
e. ensuring the SSC200 is configured to transmit either HDG or HDT
f. ensuring the GPS antenna is transmitting Magnetic Variation Data. The sentences should look
one of the sentences below, where the lowercase letter placeholders are replaced with numerical
values.
$GPRMC,hhmmss.ss,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,xxxxxx,x.x
,a,a*hh
The two underlined fields contain the magnetic variation data and must be present in order
for this sentence to be used for magnetic variation.
$GPVTG,x.x
,T,x.x,M,x.x,N,x.x,K,a*hh
The two underlined fields contain the true and magnetic course over ground data. Both
values must be present in order for this sentence to be used for magnetic variation.
Manual Variation
1. Connect the SSC200 to the PC's serial port and obtain the “cmd>” prompt per the instructions in
Appendix C.
2. To program the SSC200 with a manually magnetic variation value, type the following sentence