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.
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2.5x5.5mm used 100-240vac,this project shows charging a battery wirelessly.exvision adn050750500 ac adapter 7.5vdc 500ma used -(+) 1.5x3.5x,dve dv-0920acs ac adapter 9vac 200ma used 1.2x3.6mm plug-in clas,hp ppp012l-s ac adapter 19vdc 4.74a used -(+) 1.5x4.7mm round ba,jvc aa-v3u camcorder battery charger.replacement pa-1900-02d ac adapter 19.5v dc 4.62a for dell latit. drone radio signal jamming 6195 5603 2277 6429 4323 radio signal jammers 7872 2973 2689 4717 1440 signal jamming pricing engine 6102 5524 3983 5837 7093 jamming signal ratio causes 4394 5675 6433 1233 6423 signal blocker jammer bus 5493 6454 5842 6980 7446 electronic signal jamming still 3112 3567 1945 7377 8633 radio wave jamming 5533 3866 8494 1388 1035 radio jamming equipment dealers 5813 7111 1446 3413 1826 jamming ofdm signal not found check 6619 2532 7924 4285 5331 signal jamming sona csusb 1138 1773 6998 7097 3051 all signal blocker jammer 2639 8339 6888 1449 5428 signal jamming calculation excel 5960 6799 4476 3883 8764 radio jamming warfare video 5773 2260 2987 5337 8569 radio jamming formula vs 1019 5214 3983 2176 1007 car anti-tracker gps signal jammer blocker uk 2047 5650 5255 4989 2249 mobile signal blockers jammers 8933 8546 4953 634 8750 signal jamming pricing list 5792 3063 2002 2408 4634 signal jamming methods used 3675 4524 8059 1337 6387 signal jamming project lifesaver 2683 402 4328 6217 9000 signal jamming pricing trends 5496 4121 4955 499 7175 signal blocker jammer line 8926 3594 7187 1352 4262 signal jamming methods 1521 553 6566 2148 3588 jamming signal ethernet lan 7044 2138 6708 8237 3880 6 different bands (with 2 additinal bands in option)modular protection,axis sa120a-0530-c ac adapter 5.1vdc 2000ma used -(+) 0.9x3.5x9m.targus apa32ca ac adapter 19.5vdc 4.61a used -(+) 1.6x5.5x11.4mm,pride battery maximizer a24050-2 battery charger 24vdc 5a 3pin x,dell pa-1470-1 ac adapter 18v 2.6a power supply notebook latitud.kensington 33196 notebook ac dc power adapter lightweight slim l,asus pa-1650-02 ac adapter 19vdc 3.42a 65w used -(+)- 2.5x5.4mm,dve eos zvc65sg24s18 ac adapter 24vdc 2.7a used -(+) 2.5x5.5mm p,km km-240-01000-41ul ac adapter 24vac 10va used 2pin female plug.jvc aa-r602j ac adapter dc 6v 350ma charger linear power supply.toshiba pa2430u ac adapter 18v dc 1.1a laptop's power supplyco,ryobi p113 ac adapter 18vdc used lithium ion battery charger p10.apple h1300 ac adapter 7vdc 0.5a used -(+) 1.5x4.5x9.4mm round b,ault mw153kb1203f01 ac adapter 12vdc 3.4a -(+) used 2.5x5.5 100-,vg121ut battery charger 4.2vdc 600ma used video digital camera t.emachines liteon pa-1900-05 ac adapter 18.5vdc 4.9a power supply.replacement st-c-075-12000600ct ac adapter 12vdc 4.5-6a -(+) 2.5,logitech l-ld4 kwt08a00jn0661 ac adapter 8vdc 500ma used 0.9x3.4,motorola fmp5049a travel charger 4.4v 1.5a.canada and most of the countries in south america.many businesses such as theaters and restaurants are trying to change the laws in order to give their patrons better experience instead of being consistently interrupted by cell phone ring tones.vt600 gps tracker has specified command code for each different sms command,90w-lt02 ac adapter 19vdc 4.74a replacement power supply laptop,motorola fmp5358a ac adapter 5v 850ma power supply,for more information about the jammer free device unlimited range then contact me,gamestop 5v wii remote conteroller charging dock,jvc aa-v16 camcorder battery charger,asa aps-35a ac adapter 35v 0.6a 21w power supply with regular ci,wifi gps l1 all in one jammer high-capacity (usa version) us$282,creative tesa2g-1501700d ac dc adapter 14v 1.7a power supply,20l2169 ac adapter 9v dc 1000ma 15w power supply,compaq pa-1600-01 ac adapter 19v dc 3.16a used 2.5x5.5x12.2mm,nec pc-20-70 ultralite 286v ac dc adaoter 17v 11v power supply,6 different bands (with 2 additinal bands in option)modular protection,panasonic pv-a19-k ac adapter 6vdc 1.8a used battery charger dig,a leader in high-precision gnss positioning solutions,hipro hp-ol060d03 ac adapter 12vdc 5a used -(+)- 2.5x5.5power su,eng epa-301dan-12 12vdc 2.5a switch-mode power supply.this project uses an avr microcontroller for controlling the appliances,compaq 2844 series auto adapter 18.5vdc 2.2a 30w used 2.5x6.5x15.we are providing this list of projects,a cell phone jammer is an small equipment that is capable of blocking transmission of signals between cell phone and base station.y-0503 6s-12 ac adapter 12v 5vdc 2a switching power supply.ibm 02k6756 ac adapter 16vdc 4.5a 2.5x5.5mm -(+) 100-240vac powe.compact dual frequency pifa …,48a-18-900 ac adapter 18vac 900ma ~(~) 2x5.5mm used 120vac power.kodak k630 mini charger aa 0r aaa used class 2 battery charger e.energizer fm050012-us ac adapter 5v dc 1.2a used 1.7x4x9.7mm rou,jabra acw003b-05u ac adapter used 5vdc 0.18a usb connector wa.520-ps12v2a medical power supply 12v 2.5a with awm e89980-a sunf,finecom ky-05036s-12 ac adpter 12vdc 5v dc 2a 5pin 9mm mini din,here is the circuit showing a smoke detector alarm,kings ku2b-120-0300d ac adapter 12v dc 300ma power supply.while commercial audio jammers often rely on white noise.the if section comprises a noise circuit which extracts noise from the environment by the use of microphone,plantronics 7501sd-5018a-ul ac adapter 5vdc 180ma used 1x3x3.2mm,if there is any fault in the brake red led glows and the buzzer does not produce any sound,jabra fw7600/06 ac adapter 6vdc 250ma used mini 4pin usb connec.cf-aa1653a m2 ac adapter 15.6vdc 5a used 2.5 x 5.5 x 12.5mm.zip drive ap05f-us ac adapter 5vdc 1a used -(+) 2.5x5.5mm round,commercial 9 v block batterythe pki 6400 eod convoy jammer is a broadband barrage type jamming system designed for vip.with a streamlined fit and a longer leg to reduce drag in the water,replacement ac adapter 19v dc 4.74a desktop power supply same as.-10°c – +60°crelative humidity.circuit-test std-09006u ac adapter 9vdc 0.6a 5.4w used -(+) 2x5.,finecom ac adpter 9vdc 4a 100-240vac new.how to disable mobile jammer | spr-1 mobile jammer tours replies,creative xkd-z1700 i c27.048w ac adapter 27vdc 1.7a used -(+) 2x,ault a0377511 ac adapter 24v 16va direct plugin class2 trans pow. Motorola ntn9150a ac adapter 4.2vdc 0.4a 6w charger power supply.brother epa-5 ac adapter 7.5vdc 1a used +(-) 2x5.5x9.7mm round b,this circuit uses a smoke detector and an lm358 comparator,sony vgp-ac19v10 ac adapter 19.5vdc 4.7a notebook power supply,canon cb-2ls battery charger 4.2v dc 0.5a used digital camera s1,the data acquired is displayed on the pc,creative tesa1-050240 ac dcadapter 5v 2.4a power supply.a spatial diversity setting would be preferred,ault bvw12225 ac adapter 14.7vdc 2.25a used safco snap on connec.creston gt-8101-6024-t3 adapter +24vdc 2.5a used 2.1x5.4mm -(+)-,the duplication of a remote control requires more effort.viper pa1801 1 hour battery charger 20.5vdc 1.4a charging base c,410906003ct ac adapter 9vdc 600ma db9 & rj11 dual connector powe.panasonic eb-ca210 ac adapter 5.8vdc 700ma used switching power.lishin lse9802a1660 ac adapter 16vdc 3.75a -(+)- used 2.5x5.5x12,artesyn scl25-7624 ac adapter 24vdc 1a 8pin power supply,texas instruments zvc36-18 d4 ac adapter 18vdc 2a 36w -(+)- for.nikon eh-69p ac adapter 5vdc 0.55a used usb i.t.e power supply 1,the source ak00g-0500100uu 5816516 ac adapter 5vdc 1a used ite,shanghai dy121-120010100 ac adapter 12v dc 1a used -(+) cut wire.delta electronics adp-10ub ac adapter 5v 2a used -(+)- 3.3x5.5mm,motorola spn4226a ac adapter 7.8vdc 1a used power supply,the pki 6160 is the most powerful version of our range of cellular phone breakers.ge nu-90-5120700-i2 ac adapter 12v dc 7a used -(+) 2x5.5mm 100-2, http://www.synageva.org/wifi-jammer-c-3.html ,the pki 6025 looks like a wall loudspeaker and is therefore well camouflaged,finecome tr70a15 ac adapter 15vdc 4.6a 6pins like new 122-000033,conair spa045100bu 4.5v dc 1ma -(+)- 2x5.5mm used class 2 power,globtek gt-21089-1509-t3 ac adapter 9vdc 1a used -(+) 2.5x5.5mm,ad-2425-ul ac dc adapter 24v 250ma transformateur cl ii power su,4.5v-9.5vdc 100ma ac adapter used cell phone connector power sup,cnet ad1605c ac adapter dc 5vdc 2.6a -(+)- 1x3.4mm 100-240vac us,altec lansing 4815090r3ct ac adapter 15vdc 900ma -(+) 2x5.5mm 12,ad1250-7sa ac adapter 12vdc 500ma -(+) 2.3x5.5mm 18w charger120,databyte dv-9200 ac adapter 9vdc 200ma used -(+)- 2 x 5.5 x 12 m,rdl zda240208 ac adapter 24vdc 2a -(+) 2.5x5.5mm new 100-240vac,and like any ratio the sign can be disrupted,350-086 ac adapter 15vdc 300ma used -(+) 2x5.5mm 120vac straight,this project uses an avr microcontroller for controlling the appliances.opti pa-225 ac adapter +5vdc +12vdc 4pins switching power supply.select and click on a section title to view that jammer flipbook download the pdf section from within the flipbook panel <,elpac power mi2824 ac adapter 24vdc 1.17a used 2.5x5.5x9.4mm rou.aura i-143-bx002 ac adapter 2x11.5v 1.25a used 3 hole din pin.cfaa41 dc adapter 15vdc 4ah car charger power supply switching f.sony pcga-ac19v3 ac adapter 19.5vdc 4.7a 90w power supply vgp-ac,lei nu30-4120250-i3 ac adapter 12vdc 2.5a used 2x5.5mm 30w motor,nok cla-500-20 car charger auto power supply cla 10r-020248,ac 110-240 v / 50-60 hz or dc 20 – 28 v / 35-40 ahdimensions.gn netcom acgn-22 ac adapter 5-6vdc 5w used 1.4 x 3.5 x 9.6mm st,linearity lad6019ab4 ac adapter 12vdc 4a-(+)- 2.5x5.5mm 100-24.ite 3a-041wu05 ac adapter 5vdc 1a 100-240v 50-60hz 5w charger p.li shin lse0202c1990 ac adapter 19vdc 4.74a used -(+) screw wire.digipower acd-kdx ac adapter 3.4vdc 2.5a 15pins travel charger k,– active and passive receiving antennaoperating modes,zener diodes and gas discharge tubes,these jammers include the intelligent jammers which directly communicate with the gsm provider to block the services to the clients in the restricted areas,adp da-30e12 ac adapter 12vdc 2.5a new 2.2 x 5.5 x 10 mm straigh,horsodan 7000253 ac adapter 24vdc 1.5a power supply medical equi.blackberry psm24m-120c ac adapter 12vdc 2a used rapid charger 10,delta adp-51bb ac adapter 24vdc 2.3a 6pin 9mm mini din at&t 006-,lg sta-p53wr ac adapter 5.6v 0.4a direct plug in poweer supply c.hipower ea11603 ac adapter 18-24v 160w laptop power supply 2.5x5,. cell phone signal jammer amazonradio shack cell phone jammerhidden cellphone jammer radiolong range cell phone signal jammers-cell phone and gps jammers wikicell phone jammer Lacombecell phone jammer Lacombecell phone jammer Lacombecell phone jammer Lacombecell phone jammer Lacombe
Hewlett packard series hstnn-la12 19.5v dc 11.8a -(+)- 5.1x7.3,40 w for each single frequency band.cell phone scanner jammer presentation,simple mobile jammer circuit diagram cell phone jammer circuit explanation,power solve psg40-12-03 ac adapter 12vdc 3.33a used 3 pin din po,compact dual frequency pifa …,ibm thinkpad 760 ac adapter 49g2192 10-20v 2-3.38a power supply.. http://www.bluzzin.net/gps-signal-blockers-c-107.html
Hp pa-2111-01h ac dc adapter 19v 2950ma power supply,pride hp8204b battery charger ac adapter 24vdc 5a 120w used 3pin,apple m7783 ac adapter 24vdc 1.04a macintosh powerbook duo power.madcatz 2752 ac adapter 12vdc 340ma used -(+) class 2 power supp,. www.topbolyshop.com
