Measurement Journal Issue 6

Note that further information on data analysis, including a complete deﬁnition of measurement methodologies to evaluate accuracy performance for this test, can be found in the second edition of the GPS Standard Positioning Service Signal Speciﬁcation.3 Radio-frequency interference: This test measures the ability of the GPS receiver to operate in the presence of interfering (jamming) signals that may be received through its input. In this test, the jamming-signal power level is increased in 1-dB increments until the ﬁrst degradation of the GPS satellite-signal tracking is detected. The jamming-signal power level is again slowly increased until the GPS receiver losses its 3D navigation ﬁx. The setup required for this test is shown in Figure 7. The GPS simulation is ﬁrst started on the E4438C. The GPS receiver is turned on and allowed to achieve a location ﬁx. The jamming signal is then added to the GPS signal at a level that is discernible to the GPS receiver and is increased in 1-dB steps. The typical data collected for this interference test includes four key items: • First satellite loss threshold (dB) • 3D navigation loss threshold (dB) • Jammer center frequency • Jammer bandwidth Receiver sensitivity: The test objective here is to verify receiver sensitivity by measuring signal strength (C/No) under various GPS-signal power levels. To obtain an accurate power level for the GPS satellite signal, the number of visible satellites should be set to one on the E4438C-409 application. The power level on the front panel of the E4438C will then accurately reﬂect the total power in the single satellite signal. The GPS simulation is ﬁrst started on the E4438C. The power level on the E4438C is set such that the GPS receiver can identify the single GPS satellite signal. The power level of the GPS satellite signal is then decreased until the GPS receiver loses tracking of the single satellite. This power level, and the corresponding GPS-receiver C/No ratio, is collected as data. Another receiver sensitivity test is to measure the power level and C/No ratio level at which the 3D location ﬁx is lost. This requires a minimum of four satellite GPS simulations. In this test, the GPS simulation is started on the E4438C with all eight satellites visible. The GPS receiver is turned on and allowed to achieve a location ﬁx. The power level of the E4438C is then decreased until the 3D location ﬁx is lost. The power level and the corresponding GPS-receiver C/No ratio is collected as data. Jamming source RF out RF combiner 50 dB attenuation DC block GPS input USB connection to PC GPS receiver PC running U-center software Figure 7. RF interference test conﬁguration 23 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Measurement Journal Issue 6

Measurement Journal Issue 6 Using a Few Words to Convey a Deeply-Held Spirit Charting a Unique Path to Technology Innovation Contents Announcing First Commercial GC/MS Metabolites Library Assessing Nonlinear Behavior Testing Combines Form and Function Testing Multiplay Networks Higher Sensitivity LC/MS Easing Military Radio Test Stepping Up Calibration Accuracy Increasing Spectrum Analyzer Bandwidth 3GPP Tool Supports TS 36 Standards The Olympic Story Spotlights Agilent's Continuing Contribution to Technology Innovation Ensuring a Level Playing Field in Competitive Sports GPS: Coming of Age Resolving Design Issues in HSPA Mobile Devices Achieving Accurate Results with Oscilloscope-Based Jitter-Analysis Software RF Handheld Testers Guarantee Traffic Stability Under Olympic-Sized Stress Conditions Utilizing LAN-Based Instrumentation to Measure Total Harmonic Distortion in Remote Facilities IMT-Advanced: 4G Wireless Takes Shape in an Olympic Year EPO Doping: A Speed Engine, Turbo-Charged by Chemistry

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