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DGPS USER SAFETY ADVISORY!!


The Coast Guard Navigation Information Service (NIS) received reports in March 97 that DGPS receivers apparently ignoring the broadcast alarm which should signal the immediate discontinuation of a particular satellite correction. In accordance with international and industry standards, the USCG DGPS broadcast sets a satellite correction to the defined "do-not-use" value of 10485.76 meters if broadcast integrity checks indicate there is a problem with that correction [RTCM SC104]. Reports indicate some user equipment does not properly recognize this "do-not-use" correction flag and instead erroneously processes it as a correction. This can result in position errors as large as 15000 meters while the receiver is in DGPS mode. Concerned users should contact the manufacturer of their equipment to determine if they require a receiver upgrade.

"This is retained as an information advisory for DGPS users (May 1, 1998)"