Spectracom GSG-5 series, User Manual With Scpi Manual

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messages broadcast by these satellites are downloaded automatically from the following public
FTP sites:
EGNOS :
ftp://131.176.49.48
WAAS
:
ftp://ftp.nstb.tc.faa.gov
MSAS :
default MT63
GAGAN :
default MT63
GSG logs into these sites anonymously. However, note that both FTP sites are likely to track and
record all FTP access, including access by GSG simulators.
The SBAS download starts when the constellation simulation of the scenario has started; not dur
ing initialization of the scenario.
Considerations
If a scenario needs SBAS messages that cannot be downloaded from these FTP sites, the scen
ario continues, but the GSG unit transmits null-messages (SBAS message type: MT63). An SBAS-
compatible receiver should still be capable of seeing the SBAS signals, but it will not find any
useful information (range corrections, time offsets, etc.) in these messages.
Because of these reasons, SBAS scenarios run best with a live Internet connection. Furthermore,
since the aforementioned FTP sites store only a limited amount of SBAS records, the start time of
SBAS scenarios has to be chosen carefully:
Usually, SBAS records that are less than a year (EGNOS)/6 months (WAAS) old, can be found
on the FTP sites mentioned above. Therefore, it is advisable to select a start time that is not older
than one year for EGNOS scenarios, and not older than 6 months for WAAS scenarios.
Moreover, the start time shall not be too close to the current time. For EGNOS, there can be a
one-day delay before the SBAS messages are published on the FTP site. For WAAS the delay
can possibly be longer (up to 3 or 4 days).
An Internet connection is not
always
needed, however: All downloaded ephemeris data and
SBAS data will be locally stored on the unit, once they have been downloaded. Hence, the next
time the same scenario runs, the ephemeris data and SBAS messages are read from the local
storage, not from the online ftp sites.
GSG will performs automatic clean-up of downloaded files, once the remaining free disc space
falls below 20% of the total disc space.
Note: The SBAS corrections are ‘applied backwards’ to the output GPS signals
by adjusting the signal ranges.
It is also possible to download the EGNOS and WAAS files from the ftp servers, and select
them for use in the scenario: The file name holds the information on the applicable time & date,
which is NOT available in the content of the file (all time is relative), and must follow these nam
ing conventions:
3.5 "Select" Menu
CHAPTER
3
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User Manual GSG-5/6 Series Rev. 26
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