SMIQ
Digital Standard GPS
1125.5555.03
D-9
2.339
PATTERN
Sets the bit pattern to be used as navigation data source provided that
PATTERN has been selected as NAVIGATION DATA SOURCE.
IEC/IEEE-bus command
:SOUR:GPS:DATA:PATT #H1234,16
DATA LIST
Selects the data list to be used as navigation data source provided that
DATA_LIST has been selected as NAVIGATION DATA SOURCE .
IEC/IEEE-bus command
:SOUR:GPS:DATA:DLIS
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2.20.3
Instructions for Generating GPS Signals
This section provides background information for generating GPS signals and is intended to facilitate
generating signals with specific characteristics as well as user prompting.
1. Generating a simple GPS signal
After the default values have been set, a cyclically repetitive GPS signal is generated for one satellite by
switching STATE to ON. Changing the C/A CODE setting enables the satellite to be simulated to be
selected from 1 to 37. The associated signal level is set under LEVEL.
Note
: To avoid any damage to connected receivers, the user must ensure that the signal level used is
not too high. A downstream attenuator pad must be connected to generate output levels below
-144 dBm.
Signals generated in this way can be recognized by a GPS receiver. However, since there are no real
navigation data on the C/A code (as standard, a bit pattern with up to 16 characters is used as the
navigation data source), only the signal level of the simulated satellite can be measured and displayed
by the receiver.
A signal of this type is usually sufficient for performing simple function tests. It should be noted,
however, that the receiver to be tested may have to be switched to a special test mode, since signals
without correct navigation data are often not indicated (on a display, for example).
2. GPS signals with pseudo navigation data
Switching NAVIGATION DATA SOURCE over to DATA_LIST enables any data lists to be selected on
SMIQ and used as navigation data. Real GPS navigation data with ephemeris and almanac information
as generated with the AlmanacUploader PC tool from Rohde & Schwarz and transmitted to SMIQ, for
example would be appropriate. The program can be downloaded from the Rohde & Schwarz Internet
page (www.rohde-schwarz.com) under Application Notes 1GP46.
When pseudo-real navigation data with a length of 37500 bits (i.e. with a total signal time of 12.5
minutes) are used, for example, satellite-specific information on position and time is transmitted, which
can be recognized by the receiver. In addition to information on the received satellite, almanac and
ephemeris data can usually be output, thereby enabling the decoding of navigation data to be checked.
Note
: The GPS signal is cyclically repeated as a function of the TRIGGER MODE. When navigation
data from data lists are used, this causes the transmitted GPS time to be set to its initial value
for each new cycle.
3. Doppler-shifted GPS signals
For enhanced receiver characteristics checking, a Doppler shift of the type that occurs with real GPS
signals can also be simulated. The relevant change to the symbol rate of the C/A code is carried out
automatically. The currently valid values for Doppler-shifted carrier frequency and symbol rate are
displayed under RESULTING FREQUENCY and RESULTING SYMBOL RATE.