production of an accurate PPS signal. The internal reference position can be established in a
number of ways.
The SL869-T timing module firmware includes an auto-survey algorithm that can determine
the reference position from a series of position fix samples. The factory default is for the
auto-survey algorithm to be enabled at start-up, whereby the module operates for at least one
hour (3600 position fixes) as a positioning receiver, after which it enters Position Hold mode
using the calculated reference position.
Commands to change the number of required samples or to disable the auto-survey algorithm
are provided and are described later in this document.
If the number of required samples is changed, or if the module is given any sort of
commanded software reset (e.g. a $PSTMHOT command) while the auto-survey algorithm is
underway, the algorithm is restarted.
If the antenna position is accurately known a priori when the SL869-T timing module is
installed, the module can be commanded into Position Hold mode and to specifiy the antenna
position as its held reference position. The module can also be configured via command to
start-up in Position Hold mode using the specified antenna position as its reference position.
Note that the auto-survey algorithm should be disabled when using a commanded reference
position.
The relevant commands are described later in this document.
It is important to note that the timing output is managed independently from the navigation
algorithm, and therefore the SL869-T timing module behaves as a positioning receiver even
while it is in Position Hold mode. Thus the reported position will reflect the antenna position
as if it were output by a standard SL869 module, which may or may not be the same as the
internally held reference position.
