CompuServe Messages

No, you're very close: the mask angle just cuts out those satellites which the rx *knows* ( from the orbit ephemerides transmitted) will be below the selected angle at the approximate location of operation. There *is* a health flag whereby the satellites flag themselves as sick ( or are told to so flag themselves by ground control) if certain self-tests are not passed. If the signal path is corrupted or interfered with, there's no easy way of detecting this except using the old surveyor's technique of over-determining the system: ie, logging as many satellites as possible in the hope that one or two bad pseudoranges will not corrupt the result too much. Rob