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Simulator Calibration and Maintenance

Simulator Calibration and Maintenance. Agenda. Calibration Calibration Overview Reference Clock Frequency Carrier Breakthrough Image Rejection Power Level Channel Alignment (PCAL) Multi-chassis Calibration Maintenance. Agenda. Calibration Calibration Overview

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Simulator Calibration and Maintenance

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  1. Simulator Calibration and Maintenance Proprietary & Confidential—Page 1

  2. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 2

  3. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 3

  4. Why Calibrate? • A GPS simulator is a complex and highly accurate piece of test equipment • It’s guaranteed accuracy will be reduced if annual alignment/calibration is ignored • The degradation in accuracy will be very small – but may be significant to your tests Proprietary & Confidential—Page 4

  5. Calibration vs Alignment • Simulators require calibration and alignment from time to time to maintain the expected high level of performance • The differences between the two are: • Calibration • Instrument adjustment relative to a certified national standard, such as output power level • Alignment • Instrument adjustment relative to itself, such as inter-channel bias and carrier breakthrough Proprietary & Confidential—Page 5

  6. Calibration Procedures • All of our products have comprehensive step-by-step alignment/calibration procedures to enable users to successfully align and calibrate their equipment • Some of the following reference documents are: • MS3022 – GSS7700 Customer Calibration Procedure • MS3031 – GSS7790 Customer Calibration Procedure • DCS0004A – GSS8000 Customer Calibration Procedure • DCS0028A – Backup of NVRAM Data (GSS8000) • DGP00703AAA – GSS6560 Customer Calibration Procedure • DGP00814AAA – GSS6100 Customer Calibration Procedure • DGP00603AAA – STR4500 (appendix H) Customer Calibration Procedure • DGP00534AAA – Reconfiguration of Dual Unit GSS7700 and STR4780 Systems • DIN00010 – Backup of Calibration Data (GSS7700) Proprietary & Confidential—Page 6

  7. Alignment/Calibration • Simulator alignment is typically performed on an annual basis to maintain the specified signal generator performance • The alignment/calibration of the is carried out for the following reasons • Periodic alignment (adjustment to ensure correct operation) • Calibration (adjustment to ensure specified accuracy) • Optional performance checks • The GSS7700/8000 series chassis’ are designed so that the customer can perform the alignment/calibration at their premises • All that is required is general purpose test equipment • Annual GSS7700/8000 alignment involves • Reference Oscillator frequency adjustment • Carrier breakthrough • Image rejection • Inter-Channel Bias confirmation • Channel power adjustment Proprietary & Confidential—Page 7

  8. Alignment/Calibration (cont.) • Prior to performing the calibration • First obtain the RF calibration offsets from the ‘Customer Specific Information Sheet’ delivered with the simulator • Next gather together the list of equipment (or equivalent) from the Calibration Procedure • Appendix A of MS3022 (GSS7700) and DCS0004A (GSS8000) • These are typically: • Frequency counter • Power meter (with low-level sensor) • 10MHz frequency standard (of higher accuracy than the GSS7700 10.23MHz internal ref osc) • Spectrum analyzer • Ensure test measurement equipment is within valid calibrated status • Make a copy of Appendix B of the Calibration Procedures to record the calibration and alignment results • Store the completed results sheet in the Simulator System Reference Manual. • E-mail a copy of the Calibration Results sheet to Spirent Applications Support for inclusion in our records. Proprietary & Confidential—Page 8

  9. Alignment/Calibration (cont.) • Prior to performing the calibration (cont.) • After gathering the equipment, power-up all test equipment so it can warm up for at least 8 hours prior to performing the calibration • This is particularly important for the 10MHz standard, if – for example – a Rubidium standard is used • This is a good time to perform the necessary back-up of the simulator chassis non-volatile random access memory (NVRAM) • This can be accessed as shown below and described in the respective NVRAM backup document • Spirent recommends you use a file name that clearly identifies the signal generator serial number and date, such as: GSS8000_SN1001_15AUG08.NVS Proprietary & Confidential—Page 9

  10. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 10

  11. Reference Oscillator Adjustment • Why? • Calibration of the simulators reference clock oscillator is important to ensure the simulator’s GPS time is accurate • If drifting out of specification, then this can have performance impacts on receiver acquisition which depends on accurate ‘GPS Time’ for instance • This also ensures that the simulators 10.23 MHz ovenized crystal oscillator (OCXO) can still lock to an external reference Proprietary & Confidential—Page 11

  12. Reference Oscillator Measurement • To measure the Reference clock oscillator, a frequency counter is used as shown to the left that is synchronized with an external frequency reference • The external frequency reference used to lock the frequency counter to must be of greater accuracy than the Simulator’s OCXO (better than +/-1x10-9) • The OCXO must be adjusted to within +/-0.02Hz of 10.23MHz • Some filtering/gate time adjustment may be required on the frequency counter to obtain this sub-Hertz resolution GSS7700 ‘Int Ref Out’ connector Proprietary & Confidential—Page 12

  13. Oscillator Adjustment • Confirm the signal generator display shows “Ext Ref Unlocked” on connection of the external frequency standard, then “Ext Ref Locked”. This could take up to 2 minutes. • After measuring the reference oscillator frequency, fine adjustments can be made as shown below • Note: Take great care not to damage the fragile adjustment screw! Note: For the GSS8000, the screw is under the Spirent Logo cover. Proprietary & Confidential—Page 13

  14. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 14

  15. Carrier Breakthrough • What is Carrier Breakthrough? • The signal generator modulates all channels onto a carrier frequency using a vector modulator • Carrier breakthrough manifests itself as unmodulated continuous waves (CW) at the RF output port. • If special care and attention is not paid to ensuring very high isolation across the system, rogue signals can be picked up at the output. • The I/Q vector modulator (which modulates all the channels onto each carrier/output) employed in the system can only offer limited isolation, and carrier breakthrough/feed through are inherent characteristics of such devices. Proprietary & Confidential—Page 15

  16. Carrier Breakthrough • How do we ensure this isn’t a problem? • Spirent Simulators are designed to ensure isolation <140dB by using high performance modulators, together with the stringent control of internal operating conditions • The user must check the carrier breakthrough of these devices to ensure continuation of optimum performance • As necessary, the user can make adjustments to reduce the carrier breakthrough by using the potentiometers accessible from underneath the signal generator, while you monitor the RF output at the relevant Mon/Cal Out port Proprietary & Confidential—Page 16

  17. Configuring the Signal Generator • Using a spectrum analyzer to monitor the carrier breakthrough, the signal generator is configured to output continuous wave (CW) signals to display the breakthrough • This is performed using the IEEE string-send utility and various commands for each channel and bank • Reference the Calibration Procedure Proprietary & Confidential—Page 17

  18. Carrier Breakthrough Adjustment • To measure the carrier breakthrough, the user needs to: • Locate the L1 signal on the Spectrum Analyzer • Switch the channel off with the IEEE command: CAL0 • Record the carrier breakthrough level for adjustment (next slide) L1 CW OFF and Breakthrough Shown on Spectrum Analyzer L1 CW Signal on Spectrum Analyzer Proprietary & Confidential—Page 18

  19. After measuring the carrier breakthrough, if adjustments are necessary, then they can be performed inside the bottom of the GSS7700/8000 as shown below Reduce the carrier breakthrough level by alternating adjustment of the L1 (or L2 and L5 if necessary) modulator carrier-null screws Adjust until the carrier breakthrough is below –110dBm Carrier Breakthrough Adjustment Proprietary & Confidential—Page 19

  20. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 20

  21. Image Rejection • The modulation process can have the effect of generating an unwanted signal, with a doppler frequency offset opposite to that of the signal • This is called the signal image and is automatically adjusted for by the signal generator • These adjustments can vary over time, it is therefore necessary to run the automatic alignment procedure • Since the signal generator channels are grouped four to a card, you need only check the first channel on each card, the remaining channels on a card use the same alignment data • Reference the Calibration Procedure for initializing the automated alignment procedure Proprietary & Confidential—Page 21

  22. Image Rejection (cont.) • Confirm the automated alignment has started by checking the signal generator display, channels will be switched on and off as the modulator is automatically aligned • This alignment may take several minutes • If the alignment fails, you will see an error message on the signal generator front panel display, record this error message and contact Spirent Applications Support. • Confirm the automated alignment has completed successfully by checking the signal generator display, ‘PCAL OK’ will be displayed in the user message box or ‘PCAL FAIL’ if the alignment was unsuccessful Proprietary & Confidential—Page 22

  23. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 23

  24. Power Level • Purpose is to ensure each front panel signal is at the specified power level. • The Front RF port is the calibrated port, but low level. • The Mon/Cal port is nominally 49 to 51 dB higher, depending upon the measured offset value at the factory • This is used for calibration purposes 50dB Proprietary & Confidential—Page 24

  25. Power Level • The Mon/Cal to RF port attenuation must be precisely measured during the factory setup. Then the Mon/Cal port can be used for all future level calibrations. • GSS7700/8000 Example: finding the Mon/Cal RFREF value used in the customer calibration. • ICD-200 specified power of an L1 C/A signal -130.0 dBm • Set channel to maximum level +20.0 dB • Put C/A code on I and Q phases +3.0 • Boost power in CAL mode +10 • L1 C/A power at RF port -97 dBm • Customer calibrates to -97dBm + RFOF on Mon/Cal port Proprietary & Confidential—Page 25

  26. Power Level • The power level calibration is done on a C/A signal. What about P/Y and M ? • The nominal code powers with respect to C/A is controlled by the firmware. • Imperfections in relative code power, due to bandwidth effects, are measured during the factory calibration. • Thus once the C/A power accuracy is re-established at the customer calibration, the P/Y and M levels are corrected implicitly. Proprietary & Confidential—Page 26

  27. Power Level Adjustment • There are no mechanical adjustments as with the GSS6560 or STR4500, rather, alignment/calibration is achieved by sending IEEE/Ethernet commands and having the GSS7700/8000 measure and adjust the absolute power as necessary • The power output is measured from the rear panel Mon/Cal ports as shown below Power meter Power sensor on Mon/Cal port Proprietary & Confidential—Page 27

  28. Power Level Adjustment (cont.) • The ‘RF reference level’ is found by adding the L1 offset figure to the-97dBm baseline level • Refer to Customer Specific Config Sheet supplied with the Simulator • Read the power meter and calculate the adjustment required to achieve the previously calculated ‘RF reference level’ • Send the command ‘%CLOG?’ to read the present CLOG value, then send CLOG n to adjust the power accordingly (CLOG increments of 10 = 0.1dB changes in power) • This test is performed for each bank (L1, L2, L5) on every 4th channel (0,4,8,12, etc.) Power meter display (note you may need to apply filtering to obtain a steady reading) Proprietary & Confidential—Page 28

  29. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 29

  30. Inter-Channel Alignment • What is Inter-Channel Bias (ICB)? • Code (and carrier) misalignment between channels. • Visualize two, simulated, co-located, cloned satellites – the arrival phases of both code and carrier, should be indistinguishable between the two – differences are ICB • How to perform Inter-channel alignment? • Executing the Channel Alignment utility in SimGEN • What is the implication of channel misalignment? • The received pseudorange will be biased resulting in receiver PVT errors Proprietary & Confidential—Page 30

  31. Automatic Channel Alignment • Also referred as Phase Calibration (PCAL), the automatic channel alignment is performed with a power nulling technique • Channel 1 generates a reference signal with inverted phase • A copy of this signal is generated on each of the other channels in turn • Ideally the reference and test signals cancel out • Any difference in level, carrier or code phase results in some signal being detected by the internal detector • The test channel is adjusted to minimize the detector reading Proprietary & Confidential—Page 31

  32. Carriers in anti-phase, codes aligned Carriers in anti-phase, codes misaligned Automatic Channel Alignment (cont.) • Pictorially what is performed during the automatic channel alignment process is shown below where the detector compares two signals at a time and adjusts the test signal until it cancels out Reference Test Detector input Proprietary & Confidential—Page 32

  33. Performing the Channel Alignment • The channel alignment utility can be accessed in SimGEN under Tools • Alternatively this can be commanded with the IEEE command: PCAL6 • Several options are available for customizing the PCAL Proprietary & Confidential—Page 33

  34. During the cal the display will scroll like this At the end of the cal the display should read PCAL OK Performing the Channel Alignment (cont.) • For the GSS7700/8000 series simulators, the automatic PCAL takes about 15 minutes • During the PCAL, the front LCD display provides various information of the calibration process as described below • Note that the results indicate “PCAL OK” at the completion Proprietary & Confidential—Page 34

  35. When Should I Do A Phase Cal? • On receipt of a Simulator, after first power on. • Note: Allow for the Oscillator to warm-up first • If the equipment has been moved or transported. • For multi-unit systems, if the system has been reconfigured. • Dual unit system is split into two singles. • Regular intervals - Depending on use • Temperature variation of lab. Doing an auto-cal at a similar temperature to the test conditions could improve performance. • Performing the auto-cal at the beginning of a work period is advised. First thing Monday morning works well for many customers. Proprietary & Confidential—Page 35

  36. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 36

  37. Multi-Chassis Calibration • Multi-chassis calibrations are performed by calibrating each unit individually • The inter-antenna bias between units does not require recalibration unless the internal RF connections have been disturbed or the interconnecting cables have been changed • It is important that the same cables are used in the same location when the units are reconfigured back to the original multi-chassis configuration Proprietary & Confidential—Page 37

  38. Channel Alignment / Phase Calibration • For systems with 2 or more units (optionally connected via a Distribution Unit) the PCAL utility also aligns the channels between the boxes • This is called the Inter-Unit Calibration process as shown below Proprietary & Confidential—Page 38

  39. Agenda • Calibration • Calibration Overview • Reference Clock Frequency • Carrier Breakthrough • Image Rejection • Power Level • Channel Alignment (PCAL) • Multi-chassis Calibration • Maintenance Proprietary & Confidential—Page 39

  40. Non-Volatile RAM (NVRAM) Backup • As the system changes and new configurations are added, it’s a good habit to perform NVRAM backups • This can be accessed in SimGEN as shown below and is used to Backup or Restore System data e.g. Calibrations, change of Timer card, etc. Proprietary & Confidential—Page 40

  41. Hardware Maintenance • Firmware Upgrades • Are dependent upon the signal generator variants • Variant B (newer): • Reference: DGP00846AAA Firmware Upgrade for Variant B Signal Generators • DGP00842AAA Loading Intel Processor Firmware • Review Release Notes for potential impacts to your test configurations • Reference: DGP00766AAB GSS7700 Firmware Release Notes • Compact Flash Upgrades • Reference: DGP00808AAA Installation of Signal Generator FLASH Cards for GSS77xx • Either require installing new Compact FLASH cards or reprogramming the FPGA Compact Flash cards with the supplied FPGA programmer Proprietary & Confidential—Page 41

  42. Software Maintenance • SimGEN • Typical updates just involve installing the latest SimGEN *.exe version on the SimGEN PC • Review Release Notes for potential impacts to your test configurations • Reference: DGP00690AAA SimGEN Software Release Notes • Updates can be download via the Spirent Support website • http://www.positioningtechnology.co.uk/support/ • There are typically several updates a year • Some updates may require firmware or FPGA FLASH updates Proprietary & Confidential—Page 42

  43. M-code Software Maintenance • SimMCODE • Typical updates just involve copying newer versions of the mcode.dll and *.exe files • Reference: DGP00782AAA SimMCODE Software User Manual • Review Release Notes in the User Manual for potential impacts to your test configurations • Reference: DGP00782AAA SimMCODE Software User Manual • Some updates may require firmware or FPGA FLASH updates • Reference: DGP00782AAA SimMCODE Software User Manual • SDS Data Server • Typical updates just involve installing newer version on SDS Data Server PC from the CD *.exe • Reference: DGP00921AAA MCode SDS Software and Hardware User Manual Proprietary & Confidential—Page 43

  44. SimINERTIAL Software Maintenance • Typical updates just involve installing the new SimINERTIAL version on the SimINERTIAL PC and copying the newer versions of the INS Sensor Model.dll and *.exe files to the SimGEN PC • Reference: DGP00818AAA SimINERTIAL User Manual • Review Release Notes in the User Manual for potential impacts to your test configurations • Reference: DGP00851AAA SimINERTIAL Software Release Notes • Honeywell Only: There may be aperiodic updates to the Honeywell ISRSII firmware to support the EGI and JSF(Nav100™) interfaces • These updates require copying the new firmware version onto the SimINERTIAL PC for use in SimINERTIAL Proprietary & Confidential—Page 44

  45. Hardware LCD BITE Display • The front display provides diagnostic messages that are used for maintenance and calibration • Large units BITE display • Note: See Hardware manual for unit specific. Proprietary & Confidential—Page 45

  46. Simulator BITE Messages • Modulator oven is not yet at working temperature • Oven1 / Oven2 / Oven3 • This is important to ensure stable temperature before performing the PCAL or other alignments • Fault in local oscillator • 2nd / 3rd LO Unlocked, 137f Unlocked, 132f Unlocked, 17f Unlocked, 15f/16 Unlocked • Fault in hardware which maintains level of IF oscillator • 17f ALC • Fault in reference oscillator hardware • F level / F Ref • 1s Tick • Faulty timing hardware Proprietary & Confidential—Page 46

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