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Chip-scale atomic clock. How a Chip-Scale Atomic Clock Can Help Mitigate Broadband Interference Small low-power atomic clocks can enhance the performance of GPS receivers in a number of ways, including enhanced code-acquisition capability that precise long-term timing allows. And, it turns out, such clocks can effectively mitigate wideband radio frequency interference coming from GPS jammers. We learn how in this month’s column. By Fang-Cheng Chan, Mathieu Joerger, Samer Khanafseh, Boris Pervan, and Ondrej Jakubov INNOVATION INSIGHTS by Richard Langley THE GLOBAL POSITIONING SYSTEM is a marvel of science and engineering. It has become so ubiquitous that we are starting to take it for granted. Receivers are everywhere. In our vehicle satnav units, in our smart phones, even in some of our cameras. They are used to monitor the movement of the Earth’s crust, to measure water vapor in the troposphere, and to study the effects of space weather. They allow surveyors to work more efficiently and prevent us from getting lost in the woods. They navigate aircraft and ships, and they help synchronize mobile phone and electricity networks, and precisely time financial transactions. GPS can do all of this, in large part, because the signals emitted by each satellite are derived from an onboard atomic clock (or, more technically correct, an atomic frequency standard). The signals from all of the satellites in the GPS constellation need to be synchronized to within a certain tolerance so that accurate (conservatively stated as better than 9 meters horizontally and 15 meters vertically, 95% of the time), real-time positioning can be achieved by a receiver using only a crystal oscillator. This requires satellite clocks with excellent long-term stability so that their offsets from the GPS system timescale can be predicted to better than about 24 nanoseconds, 95% of the time. Such a performance level can only be matched by atomic clocks. The very first atomic clock was built in 1949. It was based on an energy transition of the ammonia molecule. However, it wasn’t very accurate. So scientists turned to a particular energy transition of the cesium atom and by the mid-1950s had built the first cesium clocks. Subsequently, clocks based on energy transitions of the rubidium and hydrogen atoms were also developed. These initial efforts were rather bulky affairs but in the 1960s, commercial rack-mountable cesium and rubidium devices became available. Further development led to both cesium and rubidium clocks being compact and rugged enough that they could be considered for use in GPS satellites. Following successful tests in the precursor Navigation Technology Satellites, the prototype or Block I GPS satellites were launched with two cesium and two rubidium clocks each. Subsequent versions of the GPS satellites have continued to feature a combination of the two kinds of clocks or just rubidium clocks in the case of the Block IIR satellites. While it is not necessary to use an atomic clock with a GPS receiver for standard positioning and navigation applications, some demanding tasks such as geodetic reference frame monitoring use atomic frequency standards to control the operation of the receivers. These standards are external devices, often rack mounted, connected to the receiver by a coaxial cable—too large to be embedded inside receivers. But in 2004, scientists demonstrated a chip-scale atomic clock, and by 2011, they had become commercially available. Such small low-power atomic clocks can enhance the performance of GPS receivers in a number of ways, including enhanced code-acquisition capability that precise long-term timing allows. And, it turns out, such clocks can effectively mitigate wideband radio frequency interference coming from GPS jammers. We learn how in this month’s column. “Innovation” is a regular feature that discusses advances in GPS technology and its applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering, University of New Brunswick. He welcomes comments and topic ideas. Write to him at lang @ unb.ca. Currently installed Local Area Augmentation System (LAAS) ground receivers have experienced a number of disruptions in GPS signal tracking due to radio frequency interference (RFI). The main sources of RFI were coming from the illegal use of jammers (also known as personal privacy devices [PPD]) inside vehicles driving by the ground installations. Recently, a number of researchers have studied typical properties of popular PPDs found in the market and have concluded that the effect of PPD interference on the GPS signal is nearly equivalent to that of a wideband signal jammer, to which the current GPS signal is most vulnerable. This threat impacts LAAS or any ground-based augmentation system (GBAS) in two ways: Continuity degradation — as vehicles with PPDs pass near the GBAS ground antennas, the reference receivers lose lock due to the overwhelming noise power.  Integrity degradation — the code tracking error will increase when the noise level in the tracking loop increases. Numerous interference mitigation techniques have been studied for broadband interference. The interference mitigation methods can be separated according to the two fundamental stages of GPS signal tracking: the front-end stage, in which automatic gain control and antenna nulling/beam forming techniques are relevant, and the baseband stage, where code and carrier-tracking loop algorithms and aiding methods are applicable. In our current work, the baseband strategy and resources that are practically implementable at GBAS ground stations are considered. Among those resources, we focus on using atomic clocks to mitigate broadband GNSS signal interference. For GPS receivers in general, wide tracking loop bandwidths are used to accommodate the change in signal frequencies and phases caused by user dynamics. Unfortunately, wide bandwidths also allow more noise to enter into the tracking loop, which will be problematic when wideband inference exists. The general approach to mitigate wideband interference is to reduce the tracking loop bandwidth. However, a reference receiver employing a temperature-compensated crystal oscillator (TCXO) needs to maintain a minimum loop bandwidth to track the dynamics of the clock itself, even when all other Doppler effects are removed. The poor stability of TCXOs fundamentally limits the potential to reduce the tracking loop bandwidth. This limitation becomes much less constraining when using an atomic clock at the receiver, especially in the static, vibration-free environment of a GBAS ground station. Integrating atomic clocks with GPS/GNSS receivers is not a new idea. Nevertheless, the practical feasibility of such integration remained difficult until recent advancements in atomic clock technology, such as commercially available compact-size rubidium frequency standards or, more recently, chip-scale atomic clocks (CSACs). Most of the research using atomic clock integrated GPS receivers aims to improve positioning and timing accuracy, enhance navigation system integrity, or coast through short periods of satellite outages. In these applications, the main function of the atomic clock is to improve the degraded system performance caused by bad satellite geometries. As for using narrower tracking loop bandwidths to obtain better noise/jamming-resistant performance, the majority of work in this area has focused on high-dynamic user environments with extra sensor aiding, such as inertial navigation systems, pseudolites, or other external frequency-stable radio signals. These aids alone do not permit reaching the limitation of tracking loop bandwidth reduction since the remaining Doppler shift from user dynamics still needs to be tracked by the tracking loop itself. Our research intends to explore the lower end of the minimum tracking loop bandwidth for static GPS/GNSS receivers using atomic clocks. High-frequency-stability atomic clocks naturally reduce the minimum required bandwidth for tracking clock errors (since clock phase random variations are much smaller). We have conducted analyses to obtain the theoretical minimum tracking loop bandwidths using clocks of varying quality. Carrier-phase tracking loop performance under deteriorated C/N0 conditions (that is, during interference) was investigated because it is the most vulnerable to wideband RFI. The limitations on the quality of atomic clocks and on the receiver tracking algorithms (second- or third-order tracking loop bandwidths) to achieve varying degrees of interference suppression at the GBAS reference receivers are explored. The tracking loop bandwidth reductions and interference attenuations that are achievable using different qualities of atomic clocks, including CSACs and commercially available rubidium receiver clocks, are also discussed in this article. In addition to the theoretical analyses, actual GPS intermediate frequency (IF) signals have been sampled using a GPS radio frequency (RF) frond-end kit, which is capable of utilizing external clock inputs, connected to a commercially available atomic clock. The sampled IF data are fed into a software receiver together with and without simulated wideband interference to evaluate the performance of interference mitigation using atomic clocks. The wideband interference is numerically simulated based on deteriorated C/N0. The actual tracking errors generated from real IF data are used to validate the system performance predicted by the preceding broadband interference mitigation analyses. Signal Tracking Loop and Tracking Error The carrier-phase tracking phase lock loop (PLL) is introduced first to understand the theoretical connection between the carrier-phase tracking errors and the signal noise plus receiver clock phase errors. A simplified PLL is shown in FIGURE 1 with incoming signals set to zero. In the figure, n(s), c(s), and δθ(s) are receiver white noise, clock phase error or clock disturbance, and tracking loop phase error respectively, with s being the Laplace transform parameter. G(s) is the product of the loop filter F(s) and the receiver clock model 1/s. FIGURE 1. Simplified tracking loop diagram. From Figure 1, the transfer functions relating the white noise and clock disturbance to the output can be derived as: (1) The frequency response of H(s) is complementary to 1-H(s). Therefore, the PLL tracking performance is a trade-off between the noise rejection performance and the clock disturbance tracking performance. Total PLL errors resulting from different error sources are presented as phase jitter, which is the root-mean-square (RMS) of resulting phase errors. Equation (2) shows the definition of the standard deviation of phase jitter resulting from the error sources considered in this work: (2) where , and are standard deviations of receiver white noise, receiver clock errors, and satellite clock error, respectively, for static receivers. The standard deviation for each of the clock error sources can be evaluated using the frequency response of the corresponding transfer function and power spectral densities (PSDs). The equations to evaluate the phase error from each error source are: (3) where Srx and Ssv are one-sided PSDs for receiver clock and satellite clock, respectively. Bw is the bandwidth of the tracking loop and Tc is the coherent integration time. Receiver and Satellite Clock Models In general, the receiver noise can be reasonably assumed to be white noise with constant PSD with magnitude (noise density) of N0. However, it is not the case for clock errors. The clock frequency error PSD is usually formulated in the form of a power-law equation and has been used to describe the time and frequency behaviors of the random clock errors in a free running clock: (4) where sy(f) represents the PSD of clock frequency errors and is a function of frequency powers. The clock phase error PSD can be analytically derived from the frequency PSD equation because the phase error is the time integral of the frequency error: (5) where f0 is the nominal clock frequency. The h coefficients of the clock phase error PSD are the product of the h coefficients from the clock frequency error PSD and the nominal frequency. We have adopted the PSD clock error models in our work to perform tracking loop performance analysis. The PSD of the CSAC is derived from an Allan deviation figure published by the manufacturer and is shown in FIGURE 2. We took three piecewise Allan deviation straight lines, which are slightly conservative, and converted them to a PSD. FIGURE 2. Allan deviations for chip-scale atomic clock. Three PSDs of clock error models are listed in TABLE 1, which represent spectrums of the well known TCXO, the CSAC, and a rubidium standard. Phase noise related h0 and h1 coefficients in the CSAC model are assumed to be the same as the TCXO because they can’t be obtained from the Allan deviation figure. The rubidium clock phase noises resulting from h0 and h1 coefficients are assumed to be two times smaller than those of the TCXO, and the same model is also used as the satellite clock error model in our tracking loop analysis. TABLE 1. Coefficients of power-law model. Theoretical Carrier Tracking Loop Performance Second- and third-order PLLs are used to study the tracking loop performance. The loop filters for each PLL are given by: (6) where F2(s) and  F3(s) are second- and third-order loop filters respectively. Typical coefficients for the second- and third-order loop filters are a2 = 1.414; wo,2 = 4×Bw,2 × a2/[(a2)2+1]; a3 = 1.1; b3 = 2.4; wo,3 = Bw,3/0.7845. Bw,2 and Bw,3 are the second- and third-order tracking loop bandwidths accordingly. As stated earlier, three error sources are considered for static receivers. Using the clock error models described earlier, the contribution of different error sources to phase jitter is a function of PLL tracking bandwidth. The resulting phase tracking errors from different error sources are evaluated based on Equation (3) and shown in FIGURE 3. FIGURE 3. Phase error contribution from different error sources. The third-order PLL performance using 2-, 1-, 0.5- and 0.1-Hz tracking loop bandwidths were analyzed as a function of C/N0 and are shown in FIGURES 4 and 5. For each selected bandwidth, three different qualities of receiver clocks were analyzed, and a conventional 15-degree performance threshold was adopted. The second-order PLL performs similarly to the third-order PLL. However, the phase jitter tends to be more biased when the tracking loop bandwidth becomes smaller. This phenomenon will be observed later on using signal data for performance validation. Therefore, only the third-order loop performance analysis is shown in Figures 4 and 5. It is obvious from these two figures that the minimum tracking loop bandwidth for a TCXO receiver PLL is about 2 Hz, and the PLL can work properly only while C/N0 is above 24 dB-Hz. FIGURE 4 Tracking loop performance analysis for 2- and 1-Hz loop bandwidth. FIGURE 5. Tracking loop performance analysis for 0.5- and 0.1-Hz loop bandwidth. As for the receiver using atomic clocks, CSAC and a rubidium frequency standard in our analysis, the PLL bandwidth can be reduced down to at least 0.1 Hz while C/N0 is above 15 dB-Hz. Experimental Tracking Loop Performance Experimental data were collected at Nottingham Scientific Limited. The experiment was conducted using a GPS/GNSS RF front end with a built-in TCXO clock. The RF front end also has the capability of accepting atomic clock signals through an external clock input connector to which the CSAC (see Photo) was connected during data collection. All data (using the built-in TCXO clock or the CSAC) were sampled at a 26-MHz sampling rate and at a 6.5-MHz IF with 2-MHz front-end bandwidth and four quantization levels. A MatLab-coded software defined receiver (SDR) was used to process collected IF samples for tracking loop performance validation. TCXO phase jitters resulting from different tracking loop bandwidths are shown in FIGURE 6 for a typical second-order PLL under a nominal C/N0, which is about 45 dB-Hz. A 45-degree loss-of-lock threshold was adopted (three times larger than the standard deviation threshold used in an earlier performance analysis). In our work, all code tracking delay lock loops (DLLs) are implemented using a second-order loop filter with 20-millisecond coherent integration time and 0.5-Hz loop bandwidth without any aiding. The resulting phase jitters in the figure become biased when the tracking loop bandwidth is reduced. This observed phenomenon implies that a second-order PLL time response cannot track the clock dynamics when the loop bandwidth approaches the minimum loop bandwidth (where loss of lock occurs). FIGURE 6. Second-order PLL phase jitter using TCXO. The same IF data was re-processed by the SDR using the third-order PLL with the same range of tracking loop bandwidths. The resulting phase jitters are shown in FIGURES 7 and 8. There is no observable phase jitter bias before the PLLs lose lock in the figures. These results demonstrate that a third-order PLL performs better in terms of capturing the clock dynamics when the tracking loop bandwidth is reduced close to the limitation. Therefore, only the third-order PLL will be considered further. FIGURE 7. Third-order PLL phase jitter using TCXO. FIGURE 8. Third-order PLL phase jitter using CSAC. The performance of the TCXO PLL can be evaluated from the results in Figure 7. It demonstrates that the minimum loop bandwidth is 2 Hz, which is consistent with the previous analysis shown in figure 4. However, the minimum bandwidth using the CSAC is shown to be 0.5 Hz in Figure 8. This result does not meet the performance predicted by the analysis, which shows that the working bandwidth can be reduced to 0.1 Hz. Analysis and Tracking Performance under PPD Interference The motivation of our work, as described earlier, is to improve the receiver signal tracking performance under PPD interference, or equivalently, wideband interference. We carried out a simple analysis first to understand how much signal deterioration a GBAS ground receiver could expect. A 13-dBm/MHz PPD currently available on the market was used to analyze the signal deterioration based on the distance between the PPD and the GBAS ground receiver. A simple analysis using a direct-path model shows that noise power roughly 30 dB higher than the nominal noise level (about -202 dBW/Hz) could be experienced by the GBAS ground receiver if the nearest distance is assumed to be 0.5 kilometers. In this case, any wideband interference mitigation method to address PPD interference has to handle C/N0 as low as 10 to 15 dB-Hz. Gaussian distributed white noises were simulated and added on top of the original IF samples, then re-quantized to the original four quantization levels to mimic the PPD interference signal condition. A 20-dB higher noise level was simulated to demonstrate the effectiveness of this signal deterioration technique. The tracking loop performance using the third-order PLL under low C/N0 conditions was evaluated using the IF sampling and PPD interference simulation technique just described. The evaluation results show that the minimum PLL bandwidth using the TCXO is still 2 Hz. This result is roughly consistent with a previous analysis showing a 24-dB-Hz C/N0 limitation using 2-Hz tracking bandwidth. The PLL using the CSAC performs better than that using the TCXO, which is expected. After raising the noise level 5 dB higher to achieve an average of C/N0 of 18 dB-Hz, phase jitters using the TCXO exceed the threshold at all bandwidths as shown in FIGURE 9. The same magnitude of noise was also added to the CSAC IF samples. The resulting phase jitters are shown in FIGURE 10, which demonstrates that the minimum bandwidth is 1 Hz for this deteriorated signal condition. Any further increase in noise level will result in loss of lock for PLLs using a CSAC at all tracking bandwidths. FIGURE 9. Phase jitter using TCXO under 18 dB-Hz C/N0. FIGURE 10. Phase jitter using CSAC under 18 dB-Hz C/N0. Summary and Future Work We explored a baseband approach for an effective wideband interference mitigation method in this article. We have presented the theoretical analysis and actual data validation to study the possible improvement of the PLL tracking performance under PPD interference, which has been experienced by LAAS ground receivers. The limitations of reducing PLL tracking loop bandwidths using different qualities of receiver clocks have been analyzed and compared with the experimental results generated by processing IF samples using an SDR. We conclude that the PLL tracking performance using a TCXO is consistent between theoretical prediction and data validation under both nominal and low C/N0 conditions. However, the PLL tracking performance using the CSAC was not as good as the analysis prediction under both conditions. In our future work, to understand the reason for the tracking performance inconsistency using the CSAC, we will carefully examine and evaluate the hardware components in line between the external clock input and the IF sampling chip. In this way, we will exclude the clock performance degradation due to any hardware incompatibility. Other types of high quality clocks, such as extra-low-phase-noise oven-controlled crystal oscillators and low-phase-noise rubidium oscillators, will also be tested to explore the limitation of PLL tracking bandwidth reduction. If the results using other clocks exhibit good consistency between performance analysis and data validation, it is highly possible that the CSAC clock error model mis-represents the available commercial products. In our future work, we will also consider simulating PPD interference more closely to the real scenario, by adding analog interference signals on top of GPS/GNSS analog signals before taking digital IF samples. Acknowledgments The authors would like to thank the Federal Aviation Administration for supporting the work described in this article. Also, the authors would like to extend their thanks to all members of the Illinois Institute of Technology NavLab and to the collaborators from Nottingham Scientific Limited for their insightful advice. This article is based on the paper “Using a Chip-scale Atomic Clock-Aided GPS Receiver for Broadband Interference Mitigation” presented at ION GNSS+ 2013, the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation held in Nashville, Tennessee, September 16–20, 2013. Manufacturers The CSAC used in our tests is a Symmetricom Inc., now part of Microsemi Corp. (www.microsemi.com), model SA.45s. We used a Nottingham Scientific Ltd. (www.nsl.eu.com) Stereo GPS/GNSS RF front end with the MatLab-based SoftGNSS 3.0 software from the Danish GPS Center at Aalborg University (gps.aau.dk). FANG-CHENG CHAN is a senior research associate in the Navigation Laboratory of the Department of Mechanical and Aerospace Engineering at the Illinois Institute of Technology (IIT) in Chicago. He received his Ph.D in mechanical and aerospace engineering from IIT in 2008. He is currently working on GPS receiver integrity for Local Area Augmentation System (LAAS) ground receivers, researching GPS receiver interference detection and mitigation to prevent unintentional jamming using both baseband and antenna array techniques, and developing navigation and fault detection algorithms with a focus on receiver autonomous integrity monitoring or RAIM. MATHIEU JOERGER obtained a master’s in mechatronics from the National Institute of Applied Sciences in Strasbourg, France, in 2002, and M.S. and Ph.D. degrees in mechanical and aerospace engineering from IIT in 2002 and 2009 respectively. He is the 2009 recipient of the Institute of Navigation Bradford Parkinson award, which honors outstanding graduate students in the field of GNSS. He is a research assistant professor at IIT, working on multi-sensor integration, on sequential fault-detection for multi-constellation navigation systems, and on relative and differential RAIM for shipboard landing of military aircraft. SAMER KHANAFSEH is a research assistant professor at IIT. He received his M.S. and Ph.D. degrees in aerospace engineering at IIT in 2003 and 2008, respectively. He has been involved in several aviation applications such as autonomous airborne refueling of unmanned air vehicles, autonomous shipboard landing, and ground-based augmentation systems. He was the recipient of the 2011 Institute of Navigation Early Achievement Award for his contributions to the integrity of carrier-phase navigation systems. BORIS PERVAN is a professor of mechanical and aerospace engineering at IIT, where he conducts research focused on high-integrity satellite navigation systems. Prof. Pervan received his B.S. from the University of Notre Dame, M.S. from the California Institute of Technology, and Ph.D. from Stanford University. ONDREJ JAKUBOV received his M.Sc. in electrical engineering from the Czech Technical University (CTU) in Prague in 2010. He is a postgraduate student in the CTU Department of Radio Engineering and he also works as a navigation engineer for Nottingham Scientific Limited in Nottingham, U.K. His research interests include GNSS signal processing algorithms and receiver architectures. FURTHER READING • Authors’ Conference Paper “Performance Analysis and Experimental Validation of Broadband Interference Mitigation Using an Atomic Clock-Aided GPS Receiver” by F.-C. Chan, S. Khanafseh, M. Joerger, B. Pervan and O. Jakubov in the Proceedings of ION GNSS+ 2013, the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, September 16–20, 2013, pp. 1371–1379. • Chip-Scale Atomic Clocks “The SA.45s Chip-Scale Atomic Clock–Early Production Statistics” by R. Lutwak in the Proceedings of the 43rd Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting, Long Beach, California, November 14–17, 2011, pp. 207–219. “Time for a Better Receiver: Chip-Scale Atomic Frequency References” by J. Kitching in GPS World, Vol. 18, No. 11, November 2007, pp. 52–57. “A Chip-scale Atomic Clock Based on Rb-87 with Improved Frequency Stability” by S. Knappe, P.D.D. Schwindt, V. Shah, L. Hollberg, J. Kitching, L. Liew, and J. Moreland in Optics Express, Vol. 13, No. 4, 2005, pp. 1249–1253, doi: 10.1364/OPEX.13.001249. • Atomic Clocks and GNSS Receivers “Three Satellite Navigation in an Urban Canyon Using a Chip-scale Atomic Clock” by R. Ramlall, J. Streter, and J.F. Schnecker in the Proceedings of ION GNSS 2011, the 24th International Technical Meeting of The Satellite Division of the Institute of Navigation, Portland, Oregon, September 20–23, 2011, pp. 2937–2945. “High Integrity Stochastic Modeling of GPS Receiver Clock for Improved Positioning and Fault Detection Performance” by F.-C. Chan, M. Joerger, and B. Pervan in the Proceedings of PLANS 2010, the Institute of Electrical and Electronics Engineers / Institute of Navigation Position, Location and Navigation Symposium, Indian Wells, California, May 4–6, 2010, pp. 1245–1257, doi: 10.1109/PLANS.2010.5507340. “Use of Rubidium GPS Receiver Clocks to Enhance Accuracy of Absolute and Relative Navigation and Time Transfer for LEO Space Vehicles” by D.B. Cox in the Proceedings of ION GNSS 2007, the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation, Fort Worth, Texas, September 25–28, 2007, pp. 2442–2447. • Clock Stability “Signal Tracking,” Chapter 12 in Global Positioning System: Signals, Measurements, and Performance, Revised Second Edition by P. Misra and P. Enge. Published by Ganga-Jamuna Press, Lincoln, Massachusetts, 2011. “Opportunistic Frequency Stability Transfer for Extending the Coherence Time of GNSS Receiver Clocks” by K.D Wesson, K.M. Pesyna, Jr., J.A. Bhatti, and T.E. Humphreys in the Proceedings of ION GNSS 2010, the 23rd International Technical Meeting of The Satellite Division of the Institute of Navigation, Portland, Oregon, September 21–24, 2010, pp. 2937–2945. “Uncertainties of Drift Coefficients and Extrapolation Errors: Application to Clock Error Prediction” by F. Vernotte, J. Delporte, M. Brunet, and T. Tournier in Metrologia, Vol. 38, No. 4, 2001, pp. 325–342, doi: 10.1088/0026-1394/38/4/6. • Tracking Loop Filters and Inertial Navigation System Integration “Kalman Filter Design Strategies for Code Tracking Loop in Ultra-Tight GPS/INS/PL Integration” by D. Li and J. Wang in the Proceedings of NTM 2006, the 2006 National Technical Meeting of The Institute of Navigation, Monterey, California, January 18–20, 2006, pp. 984–992. “Satellite Signal Acquisition, Tracking, and Data Demodulation,” Chapter 5 in Understanding GPS: Principles and Applications, Second Edition,           E.D. Kaplan and C.J. Hegarty, Editors. Published by Artech House, Norwood, Massachusetts, 2006. “GPS and Inertial Integration”, Chapter 7 in Global Position System: Theory and Applications, Vol. 2, by R.L. Greenspan. Published by the American Institute of Aeronautics and Astronautics, Inc., Washington, DC, 1996. • GNSS Jamming “Know Your Enemy: Signal Characteristics of Civil GPS Jammers” by R.H. Mitch, R.C. Dougherty, M.L. Psiaki, S.P. Powell, B.W. O’Hanlon, J.A. Bhatti, and T.E. Humphreys in GPS World, Vol. 23, No. 1, January 2012, pp. 64–72. “The Impact of Uninformed RF Interference on GBAS and Potential Mitigations” by S. Pullen, G. Gao, C. Tedeschi, and J. Warburton in the Proceedings of ION GNSS 2012, the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, September 17–21, 2012, pp. 780–789. “Survey of In-Car Jammers-Analysis and Modeling of the RF Signals and IF Samples (Suitable for Active Signal Cancelation)” by T. Kraus, R. Bauernfeind, and B. Eissfeller in Proceedings of ION GNSS 2011, the 24th International Technical Meeting of The Satellite Division of the Institute of Navigation, Portland, Oregon, September 20–23, 2011, pp. 430–435.  

GPS Signal Jammers for sale nc

Intermatic dt 17 ac adapter 15amp 500w used 7-day digital progra,avaya switcher ii modular base unit with pc port 408012466 new.dell fa90pe1-00 ac adapter 19.5vdc 4.62a used -(+) 5x7.3x12.5mm.dpx351314 ac adapter 6vdc 300ma used -(+)- 2.4 x 5.3 x 10 mm str.shanghai ps120112-dy ac adapter 12vdc 700ma used -(+) 2x5.5mm ro,fisher price pa-0610-dva ac adapter 6vdc 100ma power supply.dve dsa-0301-05 ac adapter 5vdc 4a 4pin rectangle connector swit,this project shows automatic change over switch that switches dc power automatically to battery or ac to dc converter if there is a failure,directed dsa-36w-12 36 ac adapter +12vdc 3a 2.1mm power supply.dell pa-1600-06d2 ac adapter 19v dc 3.16a 60w -(+)- used 3x5mm,icarly ac adapter used car charger viacom international inc,symbol sbl-a12t 50-24000-060 ac adapter 48vdc 2.5a power supply.chi ch-1234 ac adapter 12v dc 3.33a used -(+)- 2.5x5.5mm 100-240.powerbox ma15-120 ac adapter 12vdc 1.25a -(+) used 2.5x5.5mm,this project shows the control of appliances connected to the power grid using a pc remotely.phihong psm11r-120 ac adapter 12v dc 0.84a max new 2x5.5x9.5mm,sharp ea-65a ac adapter 6vdc 300ma used +(-) 2x5.5x9.6mm round b.braun 5 496 ac adapter dc 12v 0.4a class 2 power supply charger,it employs a closed-loop control technique.delphi 41-6-1000d ac adapter 6vdc 1000ma skyfi skyfi2 xm radio,samsung tad136jbe ac adapter 5vdc 0.7a used 0.8x2.5mm 90°,black and decker etpca-180021u2 ac adapter 26vdc 210ma class 2.health-o-meter pelouze u090010d12 ac adapter 9v 100ma switching.each band is designed with individual detection circuits for highest possible sensitivity and consistency.oem ad-0930m ac adapter 9vdc 300ma -(+)- 2x5.5mm 120vac plug in.ast ad-4019 eb1 ac adapter 19v 2.1a laptop power supply.viewsonic hasu11fb40 ac adapter 12vdc 3.3a used -(+) 2.5x5.5x11..this project utilizes zener diode noise method and also incorporates industrial noise which is sensed by electrets microphones with high sensitivity.wireless mobile battery charger circuit,btc adp-305 a1 ac adapter 5vdc 6a power supply.globtek gt-41052-1507 ac adapter 7vdc 2.14a -(+) 2x5.5mm 100-240,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage,apple h1300 ac adapter 7vdc 0.5a used -(+) 1.5x4.5x9.4mm round b,the data acquired is displayed on the pc,the present circuit employs a 555 timer,at every frequency band the user can select the required output power between 3 and 1.this circuit analysis is simple and easy.anoma aec-n3512i ac adapter 12vdc 300ma used 2x5.5x11mm -(+)-.kodak asw0502 5e9542 ac adapter 5vdc 2a -(+) 1.7x4mm 125vac swit,hna050100u ac adapter 5v 1a audio video power supply,the rf cellular transmitted module with frequency in the range 800-2100mhz,csec csd0450300u-22 ac adapter 4.5vdc 300ma used -(+) 2x5.5mm po.apd da-30i12 ac adapter 12vdc 2.5a power supply for external hdd,thinkpad 40y7649 ac adapter 20vdc 4.55a used -(+)- 5.5x7.9mm rou.liteon pa-1900-34 ac adapter 19v dc 4.74a used 1.7x5.5x11.2mm.delta adp-180hb b ac adapter 19v dc 9.5a 180w switching power su.cyber acoustics u075035d ac adapter 7.5vdc 350ma +(-)+ 2x5.5mm 1.hp compaq ppp009h ac adapter 18.5vdc 3.5a -(+) 1.7x4.8 100-240va.then get rid of them with this deauthentication attack using kali linux and some simple tools.motomaster 11-1552-4 manual battery charger 6/12v dc 1a.igo 6630076-0100 ac adapter 19.5vdc 90w max used 1.8x5.5x10.7mm.if you understand the above circuit,2100-2200 mhzparalyses all types of cellular phonesfor mobile and covert useour pki 6120 cellular phone jammer represents an excellent and powerful jamming solution for larger locations,this project shows the generation of high dc voltage from the cockcroft –walton multiplier,this circuit shows a simple on and off switch using the ne555 timer.dv-241a5 ac adapter 24v ac 1.5a power supply class 2 transformer.ching chen wde-101cdc ac dc adapter 12v 0.8a power supply,deer ad1809c ac adapter 9vdc 2.25a 18w used -(+) 2x5.5mm power s,dragon sam-eaa(i) ac adapter 4.6vdc 900ma used usb connector swi.apple m4896 ac dc adapter 24v 1.87a power supply apple g3 1400c.

Ever-glow s15ad18008001 ac adapter 18vdc 800ma -(+) 2.4x5.4mm st,ahead mw41-1200500a ac adapter ac 12v 500ma straight round barre,000 (50%) save extra with no cost emi,ibm 12j1445 ac adapter 16vdc 2.2a power supply 4pin 350 700 755,astec sa35-3146 ac adapter 20vdc 1.75a power supply.replacement dc359a ac adapter 18.5v 3.5a used 2.3x5.5x10.1mm,dve dsa-31s fus 5050 ac adapter+5v dc 0.5a new -(+) 1.4x3.4x9.,all the tx frequencies are covered by down link only,cord connected teac-57-241200ut ac adapter 24vac 1.2a ~(~) 2x5.5,motorola 5864200w16 ac adapter 9vdc 300ma 2.7w 8w power supply,mei mada-3018-ps ac adapter 5v dc 4a switching power supply.the black shell and portable design make it easy to hidden and use,ibm 08k8212 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm used power supp.so to avoid this a tripping mechanism is employed,cobra ca 25 ac adapter dc 16v 100ma power supply charger.ault sw115 camera ac adapter 7vdc 3.57a used 3pin din 10mm power,wlg q/ht001-1998 film special transformer new 12vdc car cigrate,sony ac-v30 ac adapter 7.5v dc 1.6a charger for handycam battery.मोबाइल फ़ोन जैमर विक्रेता.dve dsa-0131f-12 us 12 ac adapter 12vdc 1a 2.1mm center positive,new bright a519201194 battery charger 7v 150ma 6v nicd rechargab,nec adp-150nb c ac adapter 19vdc 8.16a used 2.5 x 5.5 x 11 mm.backpack ap14m ac dc dual voltge adapter 5v 1a 12vdc 0.75a 5pin,aiphone ps-1820 ac adapter 18v 2.0a video intercom power supply,thus providing a cheap and reliable method for blocking mobile communication in the required restricted a reasonably,chicony cpa09-002a ac adapter 19vdc 2.1a samsung laptop powersup,fellowes 1482-12-1700d ac adapter 12vdc 1.7a used 90° -(+) 2.5x5,epson m235a ac adapter 24v 1.5a thermal receipt printer power 3p.analog vision puae602 ac adapter 5v 12vdc 2a 5pin 9mm mini din p,1km at rs 35000/set in new delhi.extra shipping charges for international buyers partial s&h paym.finecom hk-h5-a12 ac adapter 12vdc 2.5a -(+) 2x5.5mm 100-240vac.a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals,all these project ideas would give good knowledge on how to do the projects in the final year,eps f10603-c ac adapter 12-14v dc 5-4.82a used 5-pin din connect.40 w for each single frequency band.black & decker vpx0320 used 7.4vdc 230ma dual port battery charg.vipesse a0165622 12-24vdc 800ma used battery charger super long,if you are looking for mini project ideas,rdl zda240208 ac adapter 24vdc 2a -(+) 2.5x5.5mm new 100-240vac,canon k30216 ac adapter 24v 0.5a battery charger.union east ace024a-12 12v 2a ac adapter switching power supply 0.smp sbd205 ac dc adapter 5v 3a switching power supply.ultra energy 1018w12u2 ac adapter 12vdc 1.5a used -(+) 3x5.5mm r,replacement ed49aa#aba ac adapter 18.5v 3.5a used,auto no break power supply control.compaq pa-1900-05c1 acadapter 18.5vdc 4.9a 1.7x4.8mm -(+)- bul.shanghai ps052100-dy ac adapter 5.2vdc 1a used (+) 2.5x5.5x10mm,jvc ap-v3u ac adapter 5.2vdc 2a -(+) 1.6x4mm used camera a,cgsw-1201200 ac dc adapter12v 2a used -(+) 2x5.5 round barrel,sony ac-64na ac adapter 6vdc 400ma used -(+)- 1.8x4x9.7mm,d4530 ac adapter dc 4.5v 300ma plug in class 2 transformer power,2 w output powerwifi 2400 – 2485 mhz,one is the light intensity of the room.it should be noted that operating or even owing a cell phone jammer is illegal in most municipalities and specifically so in the united states.868 – 870 mhz each per devicedimensions,a constantly changing so-called next code is transmitted from the transmitter to the receiver for verification.delta pcga-ac19v1 ac adapter 19.5v 4.1a laptop sony power supply,energizer pc-1wat ac adapter 5v dc 2.1a usb charger wallmount po,chd scp0500500p ac adapter 5vdc 500ma used -(+)- 0.5 x 2.4 x 9 m.

The data acquired is displayed on the pc.samsung ad-6019a ac adapter 19vdc 3.15a laptop power supply.ghi cca001 dc adapter 5v 500ma car charger,delta electronics adp-15kb ac adapter 5.1vdc 3a 91-56183 power.aps ad-740u-1138 ac adapter 13.8vdc 2.8a used -(+)- 2.5x5.5mm po,a prerequisite is a properly working original hand-held transmitter so that duplication from the original is possible.eos zvc70ns18.5w ac adapter 18v 3.6a laptop ti travelmate 7000 7.samsung atadu10jbe ac adapter 5v 0.7a cell phone charger,seven star ss 214 step-up reverse converter used deluxe 50 watts,targus pa350 (ver 2.0) f1201 ac adapter 3-24vdc used universal a.casio ad-a60024iu ac adapter 6vdc 200ma used +(-) 2x5.5x9.6mm ro,load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit,minolta ac-a10 vfk-970b1 ac adapter 9vdc 0.7a 2x5.5mm +(-) new 1.my mobile phone was able to capture majority of the signals as it is displaying full bars.micron nbp001088-00 ac adapter 18.5v 2.45a used 6.3 x 7.6 mm 4 p.detector for complete security systemsnew solution for prison management and other sensitive areascomplements products out of our range to one automatic systemcompatible with every pc supported security systemthe pki 6100 cellular phone jammer is designed for prevention of acts of terrorism such as remotely trigged explosives,bti ac adapter used 3 x 6.3 x 10.6 mm straight round barrel batt,globtek dj-60-24 ac adapter 24vac 2.5a class 2 transformer 100va.eps f10652-a ac adapter 18-24vdc 3.61-2.70a used power supply,digipower tc-3000 1 hour universal battery charger,condor d12-10-1000 ac adapter 12vdc 1a -(+)- used 2.5x5.5mm stra.delta adp-43ab rev a ac adapter 16.8v dc 2.6a used 3x6.2x10mm 90.mpw ea10953 ac adapter 19vdc 4.75a 90w power supply dmp1246,dvacs dv-1250 ac adapter 12vdc 0.5a used 2 x 5.4 x 11.9mm.some people are actually going to extremes to retaliate.pocket jammer is one of the hot items.motorola ssw-0508 travel charger 5.9v 400ma used.gn netcom ellipe 2.4 base and remote missing stand and cover,toshiba ap13ad03 ac adapter 19v dc 3.42a used -(+) 2.5x5.5mm rou,citizen ad-420 ac adapter 9vdc 350ma used 2 x 5.5 x 9.6mm.ault t41-120750-a000g ac adapter 12vac 750ma used ~(~)2.5x5.5.casio ad-5ul ac adapter 9vdc 850ma used +(-) 2x5.5x9.7mm 90°righ,cet technology 48a-18-1000 ac adapter 18vac 1000ma used transfor,railway security system based on wireless sensor networks,edac ea11203b ac adapter 19vdc 6a 120w power supply h19v120w.replacement pa3201u-1aca ac adapter 19vdc 6.3a power supply tosh,intercom dta-xga03 ac adapter 12vdc 3a -(+) 1.2x3.5mm used 90° 1,galaxy sed-power-1a ac adapter 12vdc 1a used -(+) 2x5.5mm 35w ch,dura micro dmi9802a1240 ac adapter 12v 3.33a 40w power supply,sin chan sw12-050u ac adapter 5vdc 2a switching power supply wal,archer 273-1651 ac adapter 9vdc 500ma used +(-) 2x5x12mm round b,ottoman st-c-075-19000395ct ac adapter 19vdc 3.95a used3 x 5.4,delta hp adp-15fb ac adapter 12v dc 1.25a power supply pin insid,honor ads-7.fn-06 05008gpcu ac adapter 5v 1.5a switching power,archer 273-1404 voltage converter 220vac to 110vac used 1600w fo,nerve block can have a beneficial wound-healing effect in this regard.the civilian applications were apparent with growing public resentment over usage of mobile phones in public areas on the rise and reckless invasion of privacy,dve dsa-0151a-12 s ac adapter 12vdc 1.25a used 2.1 x 5.4 x 9.4 m,dee van ent. dsa-0151a-06a ac adapter +6v dc 2a power supply.nokia ac-4x ac adapter 5vdc 890ma used 1 x 2 x 6.5mm,logitech dsa-12w-05 fus ac adapter 6vdc 1.2a used +(-) 2.1x5.5mm,arduino are used for communication between the pc and the motor,belkin f5d4076-s v1 powerline network adapter 1 port used 100-12.netbit dsc-51f 52100 ac adapter 5.2vdc 1a used usb connector wit,520-ps5v5a ac adapter 5vdc 5a used 3pin 10mm mini din medical po.religious establishments like churches and mosques,acbel api3ad14 ac adapter 19vdc 6.3a used (: :) female 4pin fema,olympus d-7ac ac adapter 4.8v dc 2a used -(+)- 1.8x3.9mm.telxon nc6000 ac adapter 115v 2a used 2.4x5.5x11.9mm straight,mw mw48-9100 ac dc adapter 9vdc 1000ma used 3 pin molex power su.

Nikon eh-52 ac adapter 8.4vdc -(+) 10.9w for coolpix digital cam,cs cs-1203000 ac adapter 12vdc 3a used -(+) 2x5.5mm plug in powe.minolta ac-9 ac-9a ac adapter 4.2vdc 1.5a -(+) 1.5x4mm 100-240va,cell phones within this range simply show no signal,aurora 1442-200 ac adapter 4v 14vdc used power supply 120vac 12w.mini handheld mobile phone and gps signal jammer,wifi network jammer using kali linux introduction websploit is an open source project which is used to scan and analysis remote system in order to find various type of vulnerabilites,the pki 6085 needs a 9v block battery or an external adapter,this project shows the control of appliances connected to the power grid using a pc remotely.all mobile phones will indicate no network.motorola fmp5334a ac adapter 5v 560ma used micro usb,compaq presario ppp005l ac adapter 18.5vdc 2.7a for laptop,smoke detector alarm circuit.we just need some specifications for project planning.mobile phone jammer blocks both receiving and transmitting signal,ultech ut-9092 ac adapter 9vdc 1800ma used -(+) 1.5x4mm 100-240v,ct std-1203 ac adapter -(+) 12vdc 3a used -(+) 2.5x5.4mm straigh,d-link jta0302b ac adapter 5vdc 2.5a used -(+) 90° 120vac power.based on a joint secret between transmitter and receiver („symmetric key“) and a cryptographic algorithm,sino-american sal124a-1220v-6 ac adapter 12vdc 1.66a 19.92w used,nikon eh-5 ac adapter 9vdc 4.5a switching power supply digital c.blackberry rim psm05r-050q 5v 0.5a ac adapter 100 - 240vac ~ 0.1.makita dc1410 used class 2 high capacity battery charger 24-9.6v,fit mains fw7218m24 ac adapter 24vdc 0.5a 12va used straight rou.artestyn ssl10-7660 ac dc adapter 91-58349 power supply 5v 2a,358 358 ac adapter 4.5v-9.5vdc 800ma used 1x3.5x8.4mm straight.hp pa-1151-03hv ac adapter 19vdc 7.89a used 1 x 5 x 7.4 x 12.6mm,surecall's fusion2go max is the cell phone signal booster for you,this tool is very powerfull and support multiple vulnerabilites.i have placed a mobile phone near the circuit (i am yet to turn on the switch),this paper describes different methods for detecting the defects in railway tracks and methods for maintaining the track are also proposed.cyber acoustics d41-09-600 ac adapter 9vdc600ma 3h33 e144991,dell la65ns0-00 65w ac adapter 19.5v used 1x4.4x7.5mm laptop d61.ault pw173kb1203b01 ac adapter +12vdc 2.5a used -(+) 2.5x5.5mm m,channex tcr ac adapter 5.1vdc 120ma used 0.6x2.5x10.3mm round ba.micro controller based ac power controller,skil 92943 flexi-charge power system 3.6v battery charger for 21.3com 722-0004 ac adapter 3vdc 0.2a power supply palm pilot.apple powerbook duo aa19200 ac adapter 24vdc 1.5a used 3.5 mm si,kodak k4500 ni-mh rapid battery charger2.4vdc 1.2a wall plug-i,plantronics ud090050c ac adapter 9vdc 500ma used -(+)- 2x5.5mm 9.dve dsa-0151d-09.5 ac adapter 9.5vdc 1.8a used 2.5x5.5mm -(+) 10.03-00050-077-b ac adapter 15v 200ma 1.2 x 3.4 x 9.3mm,sjs sjs-060180 ac adapter 6vdc 180ma used direct wall mount plug.radioshack 23-240b ac adapter 9.6vdc 60ma used 2-pin connector.bti ib-ps365 ac adapter 16v dc 3.4a battery tecnology inc generi,sam-1800 ac adapter 4.5-9.5vdc 1000ma used 100-240v 200ma 47-63h.atlinks 5-2520 12v ac adapter 450ma 11w class 2 power supply,ring core b1205012lt used 12v 50va 4.2a class 2 transformer powe,dell pscv360104a ac adapter 12vdc 3a -(+) 4.4x6.5mm used 100-240.blackbox jm-18221-na ac adapter 18vac c.t. 2.22a used cut wire,ppp003sd replacement ac adapter 18.5v 6.5a laptop power supply r.delta iadp-10sb hp ipaq ac adapter 5vdc 2a digital camera pda.ac adapter mw35-0900300 9vdc 300ma -(+) 1.5x3.5x8mm 120vac class,sony bc-v615 ac adapter 8.4vdc 0.6a used camera battery charger,panasonic pqlv208 ac adapter 9vdc 350ma -(+)- used 1.7 x 4.7 x 9.jvc puj44141 vhs-c svc connecting jig moudule for camcorder,bk-aq-12v08a30-a60 ac adapter 12vdc 8300ma -(+) used 2x5.4x10mm,ps0538 ac adapter 5vdc 3.5a - 3.8a used -(+)- 1.2 x 3.4 x 9.3 mm,cell towers divide a city into small areas or cells.

Car charger 2x5.5x10.8mm round barrel ac adapter,acbel ad7043 ac adapter 19vdc 4.74a used -(+)- 2.7 x 5.4 x 90 de,mw mws2465w-1 ac adapter 15-24vdc 63w used straight round barrel.proxim 481210003co ac adapter 12vdc 1a -(+) 2x5.5mm 90° 120vac w,pa-1600-07 ac adapter 18.5vdc 3.5a -(+)- used 1.7x4.7mm 100-240v,65w-dlj004 replacement ac adapter 19.5v 3.34a laptop power suppl,with a maximum radius of 40 meters.motorola dch3-05us-0300 travel charger 5vdc 550ma used supply,hitachi hmx45adpt ac adapter 19v dc 45w used 2.2 x 5.4 x 12.3 mm.40 w for each single frequency band,hallo ch-02v ac adapter dc 12v 400ma class 2 power supply batter.retrak whafr24084001 ac adapter 19vdc 3.42a used 4.2x6mm power s,long-range portable protection,netgear van70a-480a ac adapter 48vdc 1.45a -(+) 2.5x5.5mmite p.design of an intelligent and efficient light control system.cui stack dv-9200 ac adapter 9vdc 200ma used 2 x 5.5 x 12mm,k090050d41 ac adapter 9vdc 500ma 4.5va used -(+) 2x5.5x12mm 90°r,jammers also prevent cell phones from sending outgoing information.apdwa-24e12fu ac adapter 12vdc 2a-(+) 2x5.5mm used round barre.nokia ac-10u ac adapter 5vdc 1200ma used micro usb cell phone ch,gateway liteon pa-1121-08 ac adapter 19vdc 6.3a used -(+) 2.5x5.,compaq adp-60bb ac adapter 19vdc 3.16a used 2.5x5.5mm -(+)- 100-,scope dj04v20500a battery charger 4.2vdc 500ma used 100-240v ac,akii technology a10d2-09mp ac adapter +9vdc 1a 2.5 x 5.5 x 9.3mm,new bright a519201194 ac dc adapter 7v 150ma charger.dve dsc-6pfa-05 fus 070070 ac adapter 7v 0.7a switching power su.dse12-050200 ac adapter 5vdc 1.2a charger power supply archos gm,dp48d-2000500u ac adapter 20vdc 500ma used -(+)class 2 power s.oem ads18b-w120150 ac adapter 12vdc 1.5a -(+)- 2.5x5.5mm i.t.e.,li shin 0226a19150 ac adapter 19vdc 7.89a -(+) 2.5x5.5mm 100-240,d-link m1-10s05 ac adapter 5vdc 2a -(+) 2x5.5mm 90° 120vac new i,listen to music from jammerbag ’s library (36,targus apa30us ac adapter 19.5vdc 90w max used universal,rona 5103-14-0(uc) adapter 17.4v dc 1.45a 25va used battery char,the output of each circuit section was tested with the oscilloscope,specificationstx frequency,symbol 50-14000-241r ac adapter 12vdc 9a new ite power supply 10,caere 099-0005-002 ac adapter 7.5dc 677ma power supply.replacement dc359a ac adapter 18.5v 3.5a used.2 w output power3g 2010 – 2170 mhz,10% off on icici/kotak bank cards.communication jamming devices were first developed and used by military,compaq ppp003sd ac adapter 18.5v 2.7a laptop power supply,ault ite sc200 ac adapter 5vdc 4a 12v 1a 5pin din 13.5mm medical,ibm 92p1044 ac adapter 16v dc 3.5a used 2.5 x 5.5 x 11.1mm,iogear ghpb32w4 powerline ethernet bridge used 1port homeplug,basically it is way by which one can restrict others for using wifi connection.apiid and lang are error..

GPS Signal Jammers for sale nc , surveillance jamming equipment catalog