Agilent Technologies E4428C, Руководство пользователя

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356 Chapter 11
GPS Modulation
Real Time GPS
User Files
You can create data files internally in the ESG or create them externally and download them to the ESG. In
either case, the size of user data files is limited by the amount of available ESG memory. If you develop data
files externally, you can define signal structures that are not available internally in the ESG. For example, if
you require a fully-coded signal consisting of frames structured according to GPS standards (1 frame
consisting of 5 subframes and 25 pages), you can develop this signal externally and download it to the ESG.
User files can be in either binary or bit format.
Select a data mode for your data file as you would for other data types (see “Data Modes and Subframe
Structures” on page 353 ). If files are created externally and incorporate parity bits, use the Raw data mode to
transmit the data in its original form. If your file does not contain parity bits and you want to incorporate
parity bits in the transmitted signal, select the encoded (Enc) data mode. The ESG will compute parity bits
for the last 6-bits of each word.
NOTE
If you select the encoded mode for a user file that incorporates parity bits, the parity bits
will be recomputed and their values changed.
Bit Error Rate Test Measurements
Bit error rate test (BERT) measurements require an ESG with Option UN7 (Baseband BERT) or a
customer-supplied, external BER meter. The GPS signal can be configured using either a PN9 or PN15
sequence. To avoid disrupting the sequence, use the Raw data mode so parity bits are not computed for the
subframe.
When you perform BERT measurements using an externally supplied BER meter, the ESG provides the
GPS signal to the unit under test (UUT) and the BER meter computes the error results. If the ESG with
Option UN7 is used, the ESG provides the signal and makes the BERT measurements. When the ESG
performs the BERT measurement, it accepts a clock and gate signal from the UUT as well as the data. If the
UUT cannot provide a data clock signal, the ESG can provide a clock signal from the rear panel Aux I/O
connector (refer to
“13. AUX I/O Connector” on page 41 ). When the clock signal from the ESG is used, add
a delay to the signal equal to the UUT’s processing time.
For information on setting up BERT measurements refer to “Setting Up a GPS Bit Error Rate Test” on page
361 .
For detailed information on BERT, refer to “Bit Error Rate Tester–Option UN7” on page 288 .