Operating Manual Vol 1 - ES Documentation

SMIQDigital Standard GPSPATTERNDATA LISTSets the bit pattern to be used as navigation data source provided thatPATTERN has been selected as NAVIGATION DATA SOURCE.IEC/IEEE-bus command :SOUR:GPS:DATA:PATT #H1234,16Selects the data list to be used as navigation data source provided thatDATA_LIST has been selected as NAVIGATION DATA SOURCE .IEC/IEEE-bus command :SOUR:GPS:DATA:DLIS ″name″2.20.3 Instructions for Generating GPS SignalsThis section provides background information for generating GPS signals and is intended to facilitategenerating signals with specific characteristics as well as user prompting.1. Generating a simple GPS signalAfter the default values have been set, a cyclically repetitive GPS signal is generated for one satellite byswitching STATE to ON. Changing the C/A CODE setting enables the satellite to be simulated to beselected 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 isnot 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 realnavigation data on the C/A code (as standard, a bit pattern with up to 16 characters is used as thenavigation data source), only the signal level of the simulated satellite can be measured and displayedby 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 signalswithout correct navigation data are often not indicated (on a display, for example).2. GPS signals with pseudo navigation dataSwitching NAVIGATION DATA SOURCE over to DATA_LIST enables any data lists to be selected onSMIQ and used as navigation data. Real GPS navigation data with ephemeris and almanac informationas generated with the AlmanacUploader PC tool from Rohde & Schwarz and transmitted to SMIQ, forexample would be appropriate. The program can be downloaded from the Rohde & Schwarz Internetpage (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 12.5minutes) are used, for example, satellite-specific information on position and time is transmitted, whichcan be recognized by the receiver. In addition to information on the received satellite, almanac andephemeris 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 navigationdata from data lists are used, this causes the transmitted GPS time to be set to its initial valuefor each new cycle.3. Doppler-shifted GPS signalsFor enhanced receiver characteristics checking, a Doppler shift of the type that occurs with real GPSsignals can also be simulated. The relevant change to the symbol rate of the C/A code is carried outautomatically. The currently valid values for Doppler-shifted carrier frequency and symbol rate aredisplayed under RESULTING FREQUENCY and RESULTING SYMBOL RATE.1125.5555.03 2.339D-9