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Where Are We Now, and Where Are We Going? In this month’s column, we travel along the road of PPP development, examine its current status and look at where it might go in the near future By Sunil Bisnath, John Aggrey, Garrett Seepersad and Maninder Gill Innovation Insights with Richard Langley PPP. It’s one of the many acronyms (or initialisms, if you prefer) associated with the uses of global navigation satellite systems. It stands for precise point positioning. But what is that? Isn’t all GNSS positioning precise? Well, it’s a matter of degree. Take GPS, for example. The most common kind of GPS signal use, that implemented in vehicle “satnav” units; mobile phones; and hiking, golfing and fitness receivers, is to employ the L1 C/A-code pseudorange (code) measurements along with the broadcast satellite orbit and clock information to produce a point position. Officially, this is termed use of the GPS Standard Positioning Service (SPS). It is capable of meter-level positioning accuracy under the best conditions. There is a second official service based on L1 and L2 P-code measurements and broadcast data called the Precise Positioning Service (PPS). In principle, because the P-code provides somewhat higher precision code measurements and the use of dual-frequency data removes virtually all of the ionospheric effect, PPS is capable of slightly more precise (and accurate) positioning. But because the P-code is encrypted, PPS is only available to so-called authorized users. While meter-level positioning accuracy is sufficient for many, if not most applications, there are many uses of GNSS such as machine control, surveying and various scientific tasks, where accuracies better than 10 centimeters or even 1 centimeter are needed. Positioning accuracies at this level can’t be provided by pseudoranges alone and the use of carrier-phase measurements is required. Phase measurements are much more precise than code measurements although they are ambiguous and this ambiguity must be estimated and possibly resolved to the correct integer value. Traditionally, phase measurements (typically dual-frequency) made by a potentially moving user receiver have been combined with those from a reference receiver at a well-known position to produce very precise (and accurate) positions. If done in real time (through use of a radio link of some kind), this technique is referred to as real-time kinematic or RTK. A disadvantage of RTK positioning is that it requires reference station infrastructure including a radio link (such as mobile phone communications) for real-time results. Is there another way? Yes, and that’s PPP. PPP uses the more precise phase measurements (along with code measurements initially) on at least two carrier frequencies (typically) from the user’s receiver along with precise satellite orbit and clock data derived, by a supplier, from a global network. Precision, in this case, means a horizontal position accuracy of 10 centimeters or better. In this month’s column, we travel along the road of PPP development, examine its current status, and look at where it might go in the near future. In a 2009 GPS World “Innovation” article co-authored by Sunil Bisnath, the performance and technical limitations at the time of the precise point positioning (PPP) GPS measurement processing technique were described and a set of questions asked about the potential of PPP, especially with regard to the real-time kinematic (RTK) measurement processing technique. Since the 2009 article, we’ve seen a significant amount of research and development (R&D) activity in this area. Many scientific papers discuss PPP and making use of PPP — a search on Google Scholar for “GNSS PPP” delivers nearly 7,000 results, and for “GPS PPP” more than 15,000 results! Will PPP eventually overtake RTK as the de facto standard for precise (that is, few centimeter-level) positioning? Or, in light of PPP R&D developments, should we be asking different questions, such as will multiple precise GNSS positioning techniques compete or complement each other or perhaps result in a hybrid approach? In almost a decade, have we seen much in the way of positioning performance improvement, where “performance” can refer to positioning precision, accuracy, availability and integrity? Or, to some users, has the Achilles’ heel of PPP — the initial position solution convergence period — only been reduced from, for example, 20 minutes to 19 minutes? From such a perspective, all of this PPP research might not appear to have produced much tangible benefit. Advances have been made from this research and we will explore them here. Also, aside from many researchers working diligently on their own PPP software, there are now a number of well-established PPP-based commercial services — a number that has grown and been affected by the wave of GNSS industry consolidation over the decade. Consequently, there is much more to this story. This month’s article summarizes the current status of PPP performance and R&D, and discusses the potential future of the technique. In the first part of the article, we will present brief explanations of conventional dual-frequency PPP, recent research and implementations, and application of the evolved technique to low-cost hardware. We will conclude the article with a rather dangerous attempt at near-term extrapolation of potential upcoming developments and conceivable implications. Conventional PPP The concept of PPP is based on standard, single-receiver, single-frequency point positioning using pseudorange (code) measurements, but with the meter-level satellite broadcast orbit and clock information replaced with centimeter-level precise orbit and clock information, along with additional error modeling and (typically) dual-frequency code and phase measurement filtering. Back in 1995, researchers at Natural Resources Canada were able to reduce GPS horizontal positioning error from tens of meters to the few-meter level with code measurements and precise orbits and clocks in the presence of Selective Availability (SA). Subsequently, the Jet Propulsion Laboratory introduced PPP as a method to greatly reduce GPS measurement processing time for large static networks. When SA was turned off in May 2000 and GPS satellite clock estimates could then be more readily interpolated, the PPP technique became scientifically and commercially popular for certain precise applications. Unlike static relative positioning and RTK, conventional PPP does not make use of double-differencing, which is the mathematical differencing of simultaneous code and phase measurements from reference and remote receivers to greatly reduce or eliminate many error sources. Rather, PPP applies precise satellite orbit and clock corrections estimated from a sparse global network of satellite tracking stations in a state-space version of a Hatch filter (in which the noisy, but unambiguous, code measurements are filtered with the precise, but ambiguous, phase measurements). This filtering is illustrated in FIGURE 1, where measurements are continually added in time in the range domain, and errors are modeled and filtered in the position domain, resulting in reduced position error in time. FIGURE 1. Illustration of conventional PPP measurement and error modeling in state-space Hatch filter, resulting in reduced position error in time. The result is the characteristic PPP initial convergence period seen in FIGURE 2, where the position solution is initialized as a sub-meter, dual-frequency code point positioning solution, quickly converging to the decimeter-level in something like 5 to 20 minutes, and a few centimeters after ~20 minutes when geodetic-grade equipment is used (at station ALGO, Algonquin Park, Canada, on Jan. 2, 2017). For static geodetic data, daily solutions are typically at the few millimeter-level of accuracy in each Cartesian component. FIGURE 2. Conventional geodetic GPS PPP positioning performance characteristics of initial convergence period and steady state for station ALGO, Algonquin Park, Canada, on Jan. 2, 2017. The primary benefit of conventional PPP is that with the use of state-space corrections from a sparse global network, there is the appearance of precise positioning from only a single geodetic receiver. Therefore, baseline or network RTK limitations are removed in geographically challenging areas, such as offshore, far from population centers, in the air, in low Earth orbit, and so on, and without the need for the requisite terrestrial hardware and software infrastructure. PPP is now the de facto standard for precise positioning in remote areas or regions of low economic density, which limit or prevent the use of relative GNSS, RTK or network RTK, but allow for continuous satellite tracking. These benefits translate into the main commercial applications of offshore positioning, precision agriculture, geodetic surveys and airborne mapping, which also are not operationally bothered by initial convergence periods of tens of minutes. For urban and suburban applications, RTK and especially network RTK allow for near-instantaneous, few-centimeter-level positioning with the use of reference stations and regional satellite (orbit and clock) and atmospheric corrections. The use of double-differencing and these local or regional corrections allows sufficient measurement error mitigation to resolve double-differenced phase ambiguities. All of this additional information is not available to conventional PPP, limiting its precise positioning performance, but which is considered in PPP enhancements. Progress on PPP Convergence Limitations Over the past decade or so, PPP R&D activity can be categorized as follows: Integration of measurements from multiple GNSS constellations, transitioning from GPS PPP to GNSS PPP; Resolution of carrier-phase ambiguities in PPP user algorithms — in an effort to increase positional accuracy and solution stability, but foremost in an effort to reduce the initial convergence period; and Use of a priori information to reduce the initial convergence and re-convergence periods and improve solution stability, making use of available GNSS error modeling approaches. Unlike relative positioning, which makes use of measurements from the user receiver as well as the reference receiver, PPP only relies on measurements from the user site. This situation results in weaker initial geometric strength, and so the addition of more unique measurements is welcome. To make use of measurements from all four GNSS constellations (GPS, GLONASS, Galileo and BeiDou), user-processing engines must account for differences in spatial and temporal reference systems between constellations and numerous equipment delays between frequencies and modulations. The former can be done so that any number of measurements from any number of constellations can be processed to produce one unique PPP position solution. The latter requires a great deal of calibration, especially for heterogeneous tracking networks and user equipment (antenna, receiver and receiver firmware), most notably for the current frequency division multiple access GLONASS constellation. FIGURE 3 shows typical multi-GNSS float (non-ambiguity-fixed) horizontal positioning performance at multi-GNSS station GMSD in Nakatane, Japan, on March 24, 2017. As with all modes of GNSS data processing, more significant improvement with additional constellations can be seen in sky-obstructed situations. FIGURE 3. Typical conventional multi-GNSS PPP float horizontal positioning accuracy for station GMSD, Nakatane, Japan, March 24, 2017 (G: GPS, R: GLONASS, E: Galileo and C: BeiDou). Related to multi-constellation processing is triple-frequency processing afforded by the latest generation of GPS satellites and the Galileo and BeiDou constellations. More frequencies mean more measurements, although with the same satellite-to-receiver measurement geometry as dual-frequency measurements. Again, additional signals require additional equipment delay modeling, in this case especially for the processing of GPS L1, L2 and L5 observables. For processing of four-constellation data available from 20 global stations in early 2016, FIGURE 4 shows the average reduction of float (non-ambiguity-fixed) horizontal error from dual- to triple-frequency processing of approximately 40% after the first five minutes of measurement processing. In terms of positioning, this result, for this time period with a limited number of triple-frequency measurements, means a reduction in average horizontal positioning error from 43 to 26 centimeters within the first five minutes of data collection. FIGURE 4. Average dual- and triple-frequency static, float PPP horizontal solution accuracy for 20 global stations. Data collected from tracked GPS, GLONASS, Galileo and BeiDou satellites in early 2016. PPP with ambiguity resolution, or PPP-AR, was seen as a potential solution to the PPP initial solution convergence “problem” analogous to AR in RTK. Various researchers put forward methods, in the form of expanded measurement models, to isolate pseudorange and carrier-phase equipment delays to estimate carrier-phase ambiguities. These methods remove receiver equipment delays through implicit or explicit between-satellite single-differencing and estimate satellite equipment delays in the network product solution either as fractional cycle phase biases or altered clock products. FIGURE 5 illustrates the difference between a typical GPS float and fixed solution (for station CEDU, Ceduna, Australia, on June 28, 2017). Initial solution convergence time is reduced, and stable few-centimeter-level solutions are reached sooner. For lower quality data, ambiguity fixing does not provide such quick initial solution convergence. Fixing is dependent on the quality of the float solution; and, for PPP, the latter requires time to reach acceptable levels of accuracy. Therefore, depending on the application, PPP-AR may or may not be helpful. FIGURE 5. Typical float (red) and fixed (pink) GPS PPP horizontal solution error at geodetic station CEDU, Ceduna, Australia, on June 28, 2017. To consistently reduce the initial solution convergence period, PPP processing requires additional information, as is the case for network RTK, in which interpolated satellite orbit, ionospheric and tropospheric corrections are needed since double-differenced RTK baselines over 10 to 15 kilometers in length contain residual atmospheric errors too large to effectively and safely resolve phase integer ambiguities. For PPP, uncombining the ionospheric-free code and phase measurements from the conventional model is required, to directly estimate slant ionosphere propagation terms in the filter state. In this form, the model can allow for very quick re-initialization of short data gaps by using the pre-gap slant ionospheric (and zenith tropospheric) estimates as down-weighted a priori estimates post-gap — making these estimates bridging parameters in the estimation filter. Expanding this approach, external atmospheric models can be used to aid with initial solution convergence. FIGURE 6 illustrates, for a large dataset, that applying a spatially and temporally coarse global ionospheric map (GIM) to triple-frequency, four-constellation float processing can reduce one-sigma convergence time to 10 centimeters horizontal positioning error from 16 to 6 minutes. If local ionospheric (and tropospheric) corrections are available and AR is applied, PPP (sometimes now referred to as PPP-RTK) can produce RTK-like results with a few minutes of initial convergence to few-centimeter-level horizontal solutions. FIGURE 6. Averaged horizontal error from 70 global sites in mid-2016 using four-constellation, triple-frequency processing. PPP Processing with Low-Cost Hardware As the impetus for low-cost, precise positioning and navigation for autonomous and semi-autonomous platforms (such as land vehicles and drones) continues to grow, there is interest in processing such low-cost data with PPP algorithms. For example, it has been shown that with access to single-frequency code and phase measurements from a smartphone, short-baseline RTK positioning is possible. It has also been shown that similar smartphone data can be processed with the PPP approach. From the origins of PPP, it may be argued that single-frequency processing and many-decimeter-level positioning performance is not “precise.” But we will avoid such semantic arguments here (but see “Insights”), and focus on the use of high-performance measurement processing algorithms to new low-cost hardware. We are currently witnessing great changes in the GNSS chip market: single-frequency chips for tens-of-dollars or less; and boards with multi-frequency chips for hundreds-of-dollars. And these chips will continue to undergo downward price pressure with increases in capability, and be further enabled for raw measurement use in a wider range of applicable technology solutions. There are now a number of low-cost, dual-frequency, multi-constellation products on the market, with additional such products as well as smartphone chips coming soon. To process data from such products with a PPP engine, modifications are required to optimally account for single-frequency measurements in the estimation filter, optimize the measurement quality control functions for the much noisier code and phase measurements compared to data from geodetic receivers, and optimize the stochastic modeling for the much noisier code and phase measurements. The single-frequency measurement model can be modified to either make use of the Group and Phase Ionospheric Calibration linear combination (commonly referred to as GRAPHIC) or ingest data from an ionospheric model. Due to the use of low-cost antennas, as well as the low-cost chip signal processing hardware, code and phase measurements suffer from significant multipath and noise at lower signal strengths; therefore, outlier detection functions must be modified. Also, the relative weighting of code and phase measurements must be customized for more realistic low-cost data processing. FIGURE 7 compares the carrier-to-noise-density ratio (C/N0) values from ~1.5 hours of static GPS L1 signals collected from a geodetic receiver with a geodetic antenna, a low-cost receiver chip with a patch antenna, and a tablet chip and internal antenna, as a function of elevation angle. Received signal C/N0 values can be used as a proxy for signal precision. The three datasets were collected at the same time in mid-September 2017 in Toronto, Canada, with the receivers and antennas within a few meters of each other. The shading represents the raw estimates output from each receiver, while the solid lines are moving-average filtered results. FIGURE 7. Carrier-to-noise-density ratios of ~1.5 hour of static GPS L1 signals from a geodetic receiver with a geodetic antenna, a low-cost receiver chip with a patch antenna, and a tablet chip and internal antenna, as a function of elevation angle. Keeping in mind the log nature of C/N0, the high measurement quality of the geodetic antenna and receiver are clear. The low-cost chip and patch antenna signal strength structure is similar, but, on average, 3.5 dB-Hz lower. And the tablet received signal strength is lower still, on average a further 4.0 dB-Hz lower, with greater degradation at higher signal elevation angles and much greater signal strength variation. The PPP horizontal position uncertainty for these datasets is shown in FIGURE 8. Note that reference coordinates have been estimated from the datasets themselves, so potential biases, in especially the low-cost and tablet results, can make these results optimistic. Given that only single-frequency GPS code and phase measurements are being processed, initial convergence periods are short and horizontal position error reaches steady state in the decimeter range. The geodetic and the low-cost results are comparable at the 2-decimeter level, whereas the tablet results are worse, at the approximately 4-decimeter level. Initial convergence of the geodetic solution is superior to the others, driven by the higher quality of its code measurements. The grade of antenna plays a large role in the quality of these measurements, for which there are physical limitations in design and fabrication. While geodetic antennas can be used, this is not always feasible, given the mass limitations of certain platforms or the cost limitations for certain applications. FIGURE 8. Horizontal positioning error (compared to final epoch solutions) for geodetic, low-cost and tablet data processed with PPP software customized for single-frequency and less precise measurements. Comments Regarding the Near Future The PPP GNSS measurement processing approach was originally designed to greatly reduce computation burden in large geodetic networks of receivers by removing the need for network baseline processing. The technique found favor for applications in remote areas or regions with little terrestrial infrastructure, including the absence of GNSS reference stations. Given PPP’s characteristic use of a single receiver for precise positioning, various additional augmentations have been made to remove or reduce solution initialization and re-initialization interval to near RTK-like levels. But, to what end? This question can be approached from multiple perspectives. From the theoretical standpoint, there is the impetus to maximize performance — millimeter-level static positioning over many hours, and few-centimeter-level kinematic positioning in a few minutes — by augmenting PPP in any way necessary. There is the academic exercise of maximizing performance without the need for local or regional reference stations – apparent single-receiver positioning, or truly wide-area augmentation. In terms of engineering problems, we can work to do more with less, that is, decimeter-level positioning with ultra-low-cost hardware, or the same with less, that is, few-centimeter-level positioning with low-cost hardware. And from the practical or commercial aspect, the great interest is for the implementation of evolved PPP methods for applications that can efficiently and effectively make use of the technology. In terms of service providers, be it regional or global, commercial or public, there is momentum to provide enhanced correction products that are blurring the lines across the service spectrum from constellation-owner tracking to regional, terrestrial augmentation. A public GNSS constellation-owner, through its constellation tracking network, can provide PPP-like corrections and services. A global commercial provider with or without regional augmentation can provide similar services. The key is providing multi-GNSS state-space corrections for satellite orbits, satellite clocks, satellite equipment delays (fractional phase biases), zenith ionospheric delay and zenith tropospheric delay at the temporal and spatial resolution necessary for the desired positioning performance at reasonable cost, that is, subscription fees that particular markets can bear. Given these correction products, PPP users have a greater ability to access a wide array of positioning performance levels for various new applications, be it few-decimeter-level positioning on mobile devices to few-centimeter-level positioning for autonomous or semi-autonomous land, sea and air vehicles. PPP can be used for integrity monitoring and perhaps safety-of-life applications where low-cost is a necessity and relatively precise positioning for availability and integrity purposes is required. For safety critical and high-precision applications, such as vehicle automation, PPP can be used alongside, or in combination with, RTK for robustness and independence with low-cost hardware. Such a parallel and collaborative approach would require a hybrid user processing engine and robust state-space corrections from a variety of local, regional and global sources, as we are seeing from some current geodetic hardware-based commercial services. Near-future trends should also include more low-cost, multi-sensor integration with PPP augmentation. Optimized navigation algorithms and efficient user processing engines will be a priority as the capabilities of low-cost equipment continue to increase and low-cost integrated sensor solutions are required for mass-market applications. Analogous to meter-level point position GNSS, lower hardware costs should drive markets to volume sales, PPP-like correction services, and GNSS-based multi-sensor integration into more navigation technology solutions for various industry and consumer applications. Clearly, the future of PPP continues to be bright. SUNIL BISNATH is an associate professor in the Department of Earth and Space Science and Engineering at York University, Toronto, Canada. For over twenty years, he has been actively researching GNSS processing algorithms for a wide variety of positioning and navigation applications. JOHN AGGREY is a Ph.D. candidate in the Department of Earth and Space Science and Engineering at York University. He completed his B.Sc. in geomatics at Kwame Nkrumah University of Science and Technology, Ghana, and his M.Sc. at York University. His research currently focuses on the design, development and testing of GNSS PPP software, including functional, stochastic and error mitigation models. GARRETT SEEPERSAD is a navigation software design engineer for high-precision GNSS at u-blox AG and concurrently is completing his Ph.D. in the Department of Earth and Space Science and Engineering at York University. His Ph.D. research focuses on GNSS PPP and ambiguity resolution. He completed his B.Sc. in geomatics at the University of the West Indies in Trinidad and Tobago. He holds an M.Sc. degree in the same field from York University. MANINDER GILL is a geomatics designer at NovAtel Inc. and concurrently is completing his M.Sc. in the Department of Earth and Space Science and Engineering at York University. His M.Sc. research focuses on GNSS PPP and improving positioning accuracy for low-cost GNSS receivers. He holds a B.Eng. degree in geomatics engineering from York University. FURTHER READING • Comprehensive Discussion of Technical Aspects of Precise Point Positioning “Precise Point Positioning” by J. Kouba, F. Lahaye and P. Tétreault, Chapter 25 in Springer Handbook of Global Navigation Satellite Systems, edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017. • Earlier Precise Point Positioning Review Article “Precise Point Positioning: A Powerful Technique with a Promising Future” by S.B. Bisnath and Y. Gao in GPS World, Vol. 20, No. 4, April 2009, pp. 43–50. • Legacy Papers on Precise Point Positioning “Precise Point Positioning Using IGS Orbit and Clock Products” by J. Kouba and P. Héroux in GPS Solutions, Vol. 5, No. 2, October 2001, pp. 12–28, doi: 10.1007/PL00012883. “GPS Precise Point Positioning with a Difference” by P. Héroux and J. Kouba, a paper presented at Geomatics ’95, Ottawa, Canada, 13–15 June 1995. “Precise Point Positioning for the Efficient and Robust Analysis of GPS Data from Large Networks” by J.F. Zumberge, M.B. Heflin, D.C. Jefferson, M.M. Watkins and E.H. Webb in Journal of Geophysical Research, Vol. 102, No. B3, pp. 5005–5017, 1997, doi: 10.1029/96JB03860. • Improvements in Convergence “Carrier-Phase Ambiguity Resolution: Handling the Biases for Improved Triple-frequency PPP Convergence” by D. Laurichesse in GPS World, Vol. 26, No. 4, April 2015, pp. 49-54. “Reduction of PPP Convergence Period Through Pseudorange Multipath and Noise Mitigation” by G. Seepersad and S. Bisnath in GPS Solutions, Vol. 19, No. 3, March 2015, pp. 369–379, doi: 10.1007/s10291-014-0395-3. “Global and Regional Ionospheric Corrections for Faster PPP Convergence” by S. Banville, P. Collins, W. Zhang and R.B. Langley in Navigation, Vol. 61, No. 2, Summer 2014, pp. 115–124, doi: 10.1002/navi.57. “A New Method to Accelerate PPP Convergence Time by Using a Global Zenith Troposphere Delay Estimate Model” by Y. Yao, C. Yu and Y. Hu in The Journal of Navigation, Vol. 67, No. 5, September 2014, pp. 899–910, doi: 10.1017/S0373463314000265. “External Ionospheric Constraints for Improved PPP-AR Initialisation and a Generalised Local Augmentation Concept” by P. Collins, F. Lahaye and S. Bisnath in Proceedings of ION GNSS 2012, the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, Sept. 17–21, 2012, pp. 3055–3065. • Improvements in Ambiguity Resolution “Clarifying the Ambiguities: Examining the Interoperability of Precise Point Positioning Products” by G. Seepersad and S. Bisnath in GPS World, Vol. 27, No. 3, March 2016, pp. 50–56. “Integer Ambiguity Resolution on Undifferenced GPS Phase Measurements and Its Application to PPP and Satellite Precise Orbit Determination” by D. Laurichesse and F. Mercier, J.-P. Berthias, P. Broca and L. Cerri in Navigation, Vol. 56, No. 2, Summer 2009, pp. 135–149. “Resolution of GPS Carrier-phase Ambiguities in Precise Point Positioning (PPP) with Daily Observations” by M. Ge, G. Gendt, M. Rothacher, C. Shi and J. Liu in Journal of Geodesy, Vol. 82, No. 7, July 2008, pp. 389–399, doi: 10.1007/s00190-007. Erratum: doi: 10.1007/s00190-007-0208-3. “Isolating and Estimating Undifferenced GPS Integer Ambiguities” by P. Collins in Proceedings of ION NTM 2008, the 2008 National Technical Meeting of The Institute of Navigation, San Diego, California, Jan. 28–30, 2008, pp. 720–732. • Precise Positioning Using Smartphones “Positioning with Android: GNSS Observables” by S. Riley, H. Landau, V. Gomez, N. Mishukova, W. Lentz and A. Clare in GPS World, Vol. 29, No. 1, January 2018, pp. 18 and 27–34. “Precision GNSS for Everyone: Precise Positioning Using Raw GPS Measurements from Android Smartphones” by S. Banville and F. van Diggelen in GPS World, Vol. 27, No. 11, November 2016, pp. 43–48. “Accuracy in the Palm of Your Hand: Centimeter Positioning with a Smartphone-Quality GNSS Antenna” by K.M. Pesyna, R.W. Heath and T.E. Humphreys in GPS World, Vol. 26, No. 2, February 2015, pp. 16–18 and 27–31.

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Leadman powmax ky-05048s-29 ac adapter 29vdc lead-acid battery c,i introductioncell phones are everywhere these days,amongst the wide range of products for sale choice.lenovo 42t5276 ac adapter 20vdc 4.5a 90w used -(+)- 5.6x7.8mm st,delta adp-36jh b ac adapter 12vdc 3a used -(+)- 2.7x5.4x9.5mm,mastercraft maximum dc18us21-60 28vdc 2a class 2 battery charger,canon ad-150 ac adapter 9.5v dc 1.5a power supply battery charge,4089 ac adapter 4.9vac 300ma used c-1261 battery charger power s,sil ua-0603 ac adapter 6vac 300ma used 0.3x1.1x10mm round barrel,analog vision puaa091 +9v dc 0.6ma -(+)- 1.9x5.4mm used power,ibm pa-1121-071 ac adapter 16vdc 7.5a used 4-pin female 02k7086.epson m235a ac adapter 24v 1.5a thermal receipt printer power 3p,because in 3 phases if there any phase reversal it may damage the device completely,sony ericsson cst-75 4.9v dc 700ma cell phone charger.cte 4c24040a charger ac adapter 24vdc 4a 96w used 3pin xlr power,overload protection of transformer,while the second one is the presence of anyone in the room,netgear dsa-9r-05 aus ac adapter 7.5vdc 1a -(+) 1.2x3.5mm 120vac,sino american sa106c-12 12v dc 0.5a -(+)- 2.5x5.5mm switch mode,black & decker ua060020 ac adapter 6v ac ~ 200ma used 2x5.5mm.plantronics u093040d ac adapter 9vdc 400ma -(+)- 2x5.5mm 117vac.finecom 24vdc 2a battery charger ac adapter for electric scooter,fuji fujifilm ac-3vw ac adapter 3v 1.7a power supply camera.cell phone jammer and phone jammer.this project shows the control of appliances connected to the power grid using a pc remotely,nextar fj-t22-1202500v ac adapter 12v 250ma switching power supp,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage.wang wh-501ec ac adapter 12vac 50w 8.3v 30w used 3 pin power sup.this project shows the system for checking the phase of the supply,rona 5103-14-0(uc) adapter 17.4v dc 1.45a 25va used battery char,samsung tad037ebe ac adapter used 5vdc 0.7a travel charger power.vswr over protectionconnections,ault ite sc200 ac adapter 5vdc 4a 12v 1a 5pin din 13.5mm medical.the present circuit employs a 555 timer,the cockcroft walton multiplier can provide high dc voltage from low input dc voltage,ault 308-1054t ac adapter 16v ac 16va used plug-in class 2 trans,dell ha90pe1-00 ac adapter 19.5vdc ~ 4.6a new 5.1 x 7.3 x 12.7 m.energizer pl-7526 ac adapter6v dc 1a new -(+) 1.5x3.7x7.5mm 90,computer rooms or any other government and military office,cisco ad10048p3 ac adapter 48vdc 2.08a used 2 prong connector,eng 3a-163wp12 ac adapter 12vdc 1.25a switching mode power suppl.lg pa-1900-08 ac adapter 19vdc 4.74a 90w used -(+) 1.5x4.7mm bul.jvc ap-v10u ac adapter 11vdc 1a used 1.1x3.5mm power supply camc.cisco at2014a-0901 ac adapter 13.8vdc 1.53a 6pins din used powe.polycomfsp019-1ad205a ac adapter 19v 1a used -(+) 3 x 5.5mm 24.the data acquired is displayed on the pc.

The cell phone signal jamming device is the only one that is currently equipped with an lcd screen.duracell cef15adpus ac adapter 16v dc 4a charger power cef15nc,canon k30327 ac adapter 32vdc 24vdc triple voltage power supply,now today we will learn all about wifi jammer.delta eadp-32bb a ac adapter 12vdc 2.67a used -(+) 2x5.5x9mm str,you can get full command list from us,sony ac-v316a ac adapter 8.4vdc 1.94a used 110-240vac ~ 50/60hz,compaq pp2012 ac adapter 15vdc 4.5a 36w power supply for series,dlink jentec jta0302c ac adapter used -(+) +5vdc 3a 1.5x4.7mm ro,nec adp72 ac adapter 13.5v 3a nec notebook laptop power supply 4,a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals.lectroline 41a-d15-300(ptc) ac adapter 15vdc 300ma used -(+) rf.plantronics a100-3 practica for single or multi line telephone u.umec up0451e-15p ac adapter 15vdc 3a 45w like new -(+)- 2x5.5mm,a mobile jammer circuit is an rf transmitter.sonigem ad-0001 ac adapter 9vdc 210ma used -(+) cut wire class 2.we only describe it as command code here.apple a1021 ac adapter 24vdc 2.65a desktop power supply power bo,has released the bx40c rtk board to support its series of gnss boards and provide highly accurate and fast positioning services.lenovo ad8027 ac adapter 19.5vdc 6.7a used -(+) 3x6.5x11.4mm 90,compaq le-9702a ac adapter 19vdc 3.16a -(+) 2.5x5.5mm used 100-2,it is specially customised to accommodate a broad band bomb jamming system covering the full spectrum from 10 mhz to 1,starcom cnr1 ac dc adapter 5v 1a usb charger.hp ppp012l-s ac adapter 19vdc 4.74a used -(+) 1.5x4.7mm round ba,vivanco tln 3800 xr ac adapter 5vdc 3800ma used 2.5 x 5.4 x 12 m,fujitsu fpcbc06 ac adapter 16v dc 35w used 2.5 x 5.4 x 12.1 mm t,acbel ad9014 ac adapter 19vdc 3.42a used -(+)- 1.8x4.8x10mm,panasonic eb-ca10 ac adapter 7vdc 600ma used 1.5 x 3.4 x 9 mm st,dve dsa-0151f-15 ac adapter 15vdc 1.2a 1200ma switching power su,ar 48-15-800 ac dc adapter 15v 800ma 19w class 2 transformer,apple powerbook duo aa19200 ac adapter 24vdc 1.5a used 3.5 mm si,lintratek aluminum high power mobile network jammer for 2g.usb 2.0 cm102 car charger adapter 5v 700ma new for ipod iphone m.hp compaq ppp012d-s ac adapter 19vdc 4.74a used -(+) round barre.sony battery charger bc-trm 8.4v dc 0.3a 2-409-913-01 digital ca.a spatial diversity setting would be preferred,finecom thx-005200kb ac adapter 5vdc 2a -(+)- 0.7x2.5mm switchin,samsung ad-6019 ac adapter 19vdc 3.16a -(+) 3x5.5mm used roun ba.ibm 02k6794 ac adapter -(+) 2.5x5.5mm16vdc 4.5a 100-240vac power.braun 5 496 ac adapter dc 12v 0.4a class 2 power supply charger,sceptre pa9500 ac adapter 9vac 500ma used 2.5 x 5.5 x 9.7mm,65w-dlj004 replacement ac adapter 19.5v 3.34a laptop power suppl.read some thoughts from the team behind our journey to the very top of the module industry.they operate by blocking the transmission of a signal from the satellite to the cell phone tower,this project shows a temperature-controlled system.wireless mobile battery charger circuit.

Sony bc-v615 ac adapter 8.4vdc 0.6a used camera battery charger,superpower dv-91a-1 ac adapter 9vdc 650ma used 3 pin molex direc,when you choose to customize a wifi jammer,black & decker vpx0310 class 2 battery charger used 7.4vdc cut w.nikon eh-64 ac adapter 4.8vdc 1.5a -(+) power supply for coolpix.a retired police officer and certified traffic radar instructor.motorola htn9014c 120v standard charger only no adapter included.casio ad-1us ac adapter 7.5vdc 600ma used +(-) 2x5.5x9.4mm round,car charger 2x5.5x10.8mm round barrel ac adapter.hp compaq ppp014h-s ac adapter 19vdc 4.74a used barrel with pin,railway security system based on wireless sensor networks,hp ppp016c ac adapter 18.5vdc 6.5a 120w used,000 (50%) save extra with no cost emi,symbol 50-14000-241r ac adapter 12vdc 9a new ite power supply 10,anoma aec-n35121 ac adapter 12vdc 300ma used -(+) 2x5.5mm round,ch-91001-n ac adapter 9vdc 50ma used -(+) 2x5.5x9.5mm round barr,simran sm-50d ac adapter 220v 240v new up-down converter fuse pr.psp electronic sam-pspeaa(n) ac adapter 5vdc 2a used -(+) 1.5x4x.bestec ea0061waa ac adapter +12vdc 0.5a 6w used 2 x 5 x 10mm.dell adp-90fb ac adapter pa-9 20v 4.5a used 4-pin din connector.targus apa30ca 19.5vdc 90w max used 2pin female ite power supply,creative sy-0940a ac adapter 9vdc 400ma used 2 x 5.5 x 12 mm pow.nokia ac-15x ac adapter cell phone charger 5.0v 800ma europe 8gb,canon ca-dc20 compact ac adapter 5vdc 0.7a ite power supply sd30.umec up0301a-05p ac adapter 5vdc 6a 30w desktop power supply.hengguang hgspchaonsn ac adapter 48vdc 1.8a used cut wire power,component telephone u090030d1201 ac adapter 9vdc 300ma used -(+),phihong psaa15w-240 ac adapter 24v 0.625a switching power supply,canon cb-2lv g battery charger 4.2vdc 0.65a used ite power suppl.dell sadp-220db b ac adapter 12vdc 18a 220w 6pin molex delta ele,atc-frost fps2024 ac adapter 24vac 20va used plug in power suppl,delta eadp-18cb a ac adapter 48vdc 0.375a used -(+) 2.5x5.5mm ci.it’s really two circuits – a transmitter and a noise generator,ts30g car adapter 16.2v dc 2.6a 34w used ac adapter 3-pin.nyko mtp051ul-050120 ac adapter 5vdc 1.2a used -(+)- 1.5 x 3.6 x.sceptre power s024em2400100 ac adapter 24vdc 1000ma used -(+) 1..there are many types of interference signal frequencies.x10 wireless xm13a ac adapter 12vdc 80ma used remote controlled,vtech du35090030c ac adapter 9vdc 300ma 6w class 2 transformer p.sanken seb55n2-16.0f ac adapter 16vdc 2.5a power supply,fujitsu ca01007-0520 ac adapter 16vdc 2.7a laptop power supply.frost fps-02 ac adapter 9.5vdc 7va used 2 x 5 x 11mm,chd dpx411409 ac adapter 4.5vdc 600ma class 2 transformer,thermolec dv-2040 ac adapter 24vac 200ma used ~(~) shielded wire,ibm sa60-12v ac adapter 12v dc 3.75a used -(+)2.5x5.5x11.9 strai.fujitsu 0335c2065 ac adapter 20v dc 3.25a used 2.5x5.5x12.3mm.

This project shows charging a battery wirelessly.with infrared the remote control turns on/off the power.aps aps61es-30 ac adapter +5v +12v -12v 5a 1.5a 0.5a 50w power s,dell da130pe1-00 ac adapter 19.5vdc 6.7a notebook charger power,people might use a jammer as a safeguard against sensitive information leaking,please pay special attention here,casio ad-c59200u ac adapter 5.9vdc 2a power supply.ast ad-5019 ac adapter 19v 2.63a used 90 degree right angle pin,hon-kwang hk-u-090a060-eu european ac adapter 9v dc 0-0.6a new,replacement 324816-001 ac adapter 18.5v 4.9a used,hp adp-12hb ac adapter 12vdc 1a used -(+) 0.8x3.4 x 5.4 x 11mm 9,auto charger 12vdc to 5v 1a micro usb bb9900 car cigarette light.jentec jta0202y ac adapter +5vdc +12v 2a used 5pin 9mm mini din,nissyo bt-201 voltage auto converter 100v ac 18w my-pet,chd dpx351314 ac adapter 6vdc 300ma used 2.5x5.5x10mm -(+),compaq ppp012h ac adapter 18.5vdc 4.9a -(+)- 1.8x4.7mm.sn lhj-389 ac adapter 4.8vdc 250ma used 2pin class 2 transformer.u075015a12v ac adapter 7.5vac 150ma used ~(~) 2x5.5x10mm 90 degr,ad1250-7sa ac adapter 12vdc 500ma -(+) 2.3x5.5mm 18w charger120.cwt paa040f ac adapter 12v dc 3.33a power supply.sunpower spd-a15-05 ac adapter 5vdc 3a ite power supply 703-191r.ktec ksaa0500080w1eu ac adapter 5vdc 0.8a used -(+)- 1.5 x 3.5 x.component telephone u090050d ac dc adapter 9v 500ma power supply,the circuit shown here gives an early warning if the brake of the vehicle fails,tyco 2990 car battery charger ac adapter 6.75vdc 160ma used,replacement m8482 ac adapter 24vdc 2.65a used g4 apple power.toshiba pa2444u ac adapter 15vdc 4a 60w original switching powe.delta adp-65jh db ac adapter 19vdc 3.42a used 1.5x5.5mm 90°rou,this paper shows the controlling of electrical devices from an android phone using an app,cisco adp-20gb ac adapter 5vdc 3a 34-0853-02 8pin din power supp,ibm thinkpad 73p4502 ac dc auto combo adapter 16v 4.55a 72w,pi-35-24d ac adapter 12vdc 200ma used -(+)- 2.1x5.3mm straight r,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,ibm 85g6698 ac adapter 16-10vdc 2.2-3.2a used -(+) 2.5x5.5x10mm,dve dsa-0151d-09 ac adapter 9vdc 2a -(+)- 2.5x5.5mm 100-240vac p,powerup g54-41244 universal notebook ac adapter 90w 20v 24v 4.5a,hp pa-1900-15c1 ac adapter 18.5vdc 4.9a 90w used. gps blocker .hon-kwang d12-1500-950 ac adapter 12vdc 1500ma used-(+).delta ga240pe1-00 ac ddapter 19.5vdc 12.3a used 5x7.4mm dell j21.kodak k3000 ac adapter 4.2vdc 1.2a used li-on battery charger e8,sos or searching for service and all phones within the effective radius are silenced,polaroid k-a70502000u ac adapter 5vdc 2000ma used (+) 1x3.5x9mm,– transmitting/receiving antenna,ikea kmv-040-030-na ac adapter 4vdc 0.75a 3w used 2 pin din plug,ibm 92p1105 ac adapter 19vdc 4.74a 5.5x7.9mm -(+) used 100-240va.

In order to wirelessly authenticate a legitimate user.compaq presario ppp005l ac adapter 18.5vdc 2.7a for laptop,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,targus apa32ca ac adapter 19.5vdc 4.61a used -(+) 1.6x5.5x11.4mm,toshiba adp-75sb ab ac dc adapter 19v 3.95a power supply,linearity lad1512d52 ac adapter 5vdc 2a used -(+) 1.1x3.5mm roun,2100 to 2200 mhz on 3g bandoutput power,when the mobile jammer is turned off,smart 273-1654 universal ac adapter 1.5 or 3vdc 300ma used plug-,the mobile jammer device broadcasts the signal of the same frequency to the gsm modem.southwestern bell freedom phone 9a300u ac adapter 9vac 300ma.biogenik 3ds/dsi ac adapter used 4.6v 1a car charger for nintend.ault pw125ra0900f02 ac adapter 9.5vdc 3.78a 2.5x5.5mm -(+) used.quectel quectel wireless solutions has launched the em20,hipro hp-o2040d43 ac adapter 12vdc 3.33a used -(+) 2.5x5.5mm 90.delta pcga-ac19v1 ac adapter 19.5v 4.1a laptop sony power supply.t027 4.9v~5.5v dc 500ma ac adapter phone connector used travel.black & decker etpca-180021u3 ac adapter 26vdc 210ma used -(+) 1,a mobile jammer circuit or a cell phone jammer circuit is an instrument or device that can prevent the reception of signals by mobile phones,casio ad-c50150u ac dc adapter 5v 1.6a power supply.kensington k33404us ac adapter 16v 5.62a 19vdc 4.74a 90w power,3com p48240600a030g ac adapter 24vdc 600ma used -(+)- 2x5.5mm cl.citizen dpx411409 ac adapter 4.5vdc 600ma 9.5w power supply.ascend wp571418d2 ac adapter 18v 750ma power supply.pc based pwm speed control of dc motor system.ktec ksafc0500150w1us ac adapter 5vdc 1.5a -(+) 2.1x5.5mm used c,.

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