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Handling the Biases for Improved Triple-Frequency PPP Convergence By Denis Laurichesse Precise point positioning (PPP) can be considered a viable tool in the kitbag of GPS positioning techniques. One precision aspect of PPP is its use of carrier-phase measurements rather than just pseudoranges. But there is a catch. Often many epochs of measurements are needed for a position solution to converge to a sufficiently high accuracy. In this month’s column, we look at how using measurements from three satellite frequencies rather than just two can help. INNOVATION INSIGHTS by Richard Langley PPP? WHAT’S THAT? This acronym stands for precise point positioning and, although the technique is still in development, it has evolved to a stage where it can be considered another viable tool in the kitbag of GPS positioning techniques. It is now supported by a number of receiver manufacturers and several free online PPP processing services. You might think, looking at the name, that there’s nothing particularly special about it. After all, doesn’t any kind of positioning with GPS give you a precise point position including that from a handheld receiver or a satnav device? They key word here is precise. The use of the word precise, in the context of GPS positioning, usually means getting positional information with precision and accuracy better than that afforded by the use of L1 C/A-code pseudorange measurements and the data provided in the broadcast navigation messages from the satellites. A typically small improvement in precision and accuracy can be had by using pseudoranges determined from the L2 frequency in addition to L1. This permits the real-time correction for the perturbing effect of the ionosphere. Such an improvement in positioning is embodied in the distinction between the two official GPS levels of service: the Standard Positioning Service provided through the L1 C/A-code and the Precise Positioning Service provided for “authorized” users, which requires the use of the encrypted P-code on both the L1 and L2 frequencies. Civil GPS users will have access to a similar level of service once a sufficient number of satellites transmitting the L2 Civil (L2C) code are in orbit. However, this capability will only provide meter-level accuracy. The PPP technique can do much better than this. It can do so thanks to two additional precision aspects of the technique. The first is the use of more precise (and, again, accurate) descriptions of the orbits of the satellites and the behavior of their atomic clocks than those included in the navigation messages. Such data is provided, for example, by the International GNSS Service (IGS) through its global tracking network and analysis centers. These so-called precise products are typically used to process receiver data after collection in a post-processing mode, although real-time correction streams are now being provided by the IGS and some commercial entities. Now, it’s true that a user can get high precision and accuracy in GPS positioning using the differential technique where data from one or more base or reference stations is combined with data from the user receiver. However, by using precise products and a very thorough model of the GPS observables, the PPP technique does away with the requirement for a directly accessed base station. The other precision aspect of PPP is its use of carrier-phase measurements rather than just pseudoranges. Carrier-phase measurements have a precision on the order of two magnitudes (a factor of 100) better than that of pseudoranges. But there is a catch to the use of carrier-phase measurements: they are ambiguous by an integer multiple of one cycle. Processing algorithms must resolve the value of this ambiguity and ideally fix it at its correct integer value. Unfortunately, it is difficult to do this instantaneously, and often many epochs of measurements are needed for a position solution to converge to a sufficiently high accuracy, say better than 10 centimeters. Researchers are actively working on reducing the convergence time, and in this month’s column, we look at how using measurements from three satellite frequencies rather than just two can help. “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. To contact him, see the “Contributing Editors” section on page 6. While carrier-phase measurements typically have very low noise compared to pseudorange (code) measurements, they have an inherent integer cycle ambiguity: the carrier phase, interpreted as a range measurement, is ambiguous by any number of cycles. However, integer ambiguity fixing is now routinely applied to undifferenced GPS carrier-phase measurements to achieve precise positioning. Some implementations are even available in real time. This so-called precise point positioning (PPP) technique permits ambiguity resolution at the centimeter level. With the new modernized satellites’ capabilities, performing PPP with triple-frequency measurements will be possible and, therefore, the current dual-frequency formulation will not be applicable. There is also a need for a generalized formulation of phase biases for Radio Technical Commission for Maritime Services (RTCM) State Space Representation (SSR) needs. In this RTCM framework, the definition of a standard is important to allow interoperability between the two components of a positioning system: the network side and the user side. Classical Formulation In this section, we review the formulation of the observation equations. We will use the following constants in the equations: where f1 and f2 are the two primary frequencies transmitted by all GPS satellites and c is the vacuum speed of light. For the GPS L1 and L2 bands, f1 = 154f0 and f2 = 120f0, where f0 = 10.23 MHz. The pseudorange (or code) measurements, P1 and P2, are expressed in meters, while phase measurements, L1 and L2, are expressed in cycles. In the following, we use the word “clock” to mean a time offset between a receiver or satellite clock and GPS System Time as determined from either code or phase measurements on different frequencies or some combination of them. The code and phase measurements are modeled as:   (1) where: D1 and D2 are the geometrical propagation distances between the emitter and receiver antenna phase centers at f1 and f2 including troposphere elongation, relativistic effects and so on. W is the contribution of the wind-up effect (in cycles). e is the code ionosphere elongation in meters at f1. This elongation varies with the inverse of the square of the carrier frequency and is applied with the opposite sign for phase. Δh = hi – hj is the difference between receiver i and emitter j ionosphere-free phase clocks. Δhp is the corresponding term for code clocks. Δτ = τi – τj is the difference between receiver i and emitter j offsets between the phase clocks at f1 and the ionosphere-free phase clocks. By construction, the corresponding quantity at f2 is γΔτ. Similarly, the corresponding quantity for the code is Δτp (time group delay). N1 and N2 are the two carrier-phase ambiguities. By definition, these ambiguities are integers. Unambiguous phase measurements are therefore L1 + N1 and L2 + N2. Equations (1) take into account all the biases related to delays and clock offsets. The four independent parameters, Δh, Δτ, Δhp, and Δτp, are equivalent to the definition of one clock per observable. However, our choice of parameters emphasizes the specific nature of the problem by identifying reference clocks for code and phase (Δhp and Δh) and the corresponding hardware offsets (Δτp and Δτ). These offsets are assumed to vary slowly with time, with limited amplitudes. The measured widelane ambiguity,  , (also called the Melbourne-Wübbena widelane) can be written as: (2) where Nw is the integer widelane ambiguity, μ j is the constant widelane delay for satellite j and μi is the widelane delay for receiver i (which is fairly stable for good quality geodetic receivers). The symbol  means that all quantities have been averaged over a satellite pass. Integer widelane ambiguities are then easily identified from averaged measured widelanes corrected for satellite widelane delays. Once integer widelane ambiguities are known, the ionosphere-free phase combination can be expressed as   (3) where     is the ionosphere-free phase combination computed using the known Nw ambiguity, Dc is the propagation distance, hi is the receiver clock and h j is the satellite clock. N1 is the remaining ambiguity associated to the ionosphere-free wavelength λc (10.7 centimeters). The complete problem is thus transformed into a single-frequency problem with wavelength λc and without any ionosphere contribution. Many algorithms can be used to solve Equation (3) using data from a network of stations. If Dc is known with sufficient accuracy (typically a few centimeters, which can be achieved using a good floating-point or real-valued ambiguity solution), it is possible to simultaneously solve for N1 , hi and h j. The properties of such a solution have been studied in detail. A very interesting property of the h j satellite clocks is, in particular, the capability to directly fix (to the correct integer value) the N1 values of a receiver that was not part of the initial network. The majority of the precise-point-positioning ambiguity-resolution (PPP-AR) implementations are based on the identification and use of the two quantities μ j and h j. These quantities may be called widelane biases and integer phase clocks, a decoupled clock model or uncalibrated phase delays, but they are all of the same nature. A Real-Time PPP-AR Implementation A PPP-AR technique was successfully implemented by the Centre National d’Etudes Spatiales (CNES) in real time in the so-called PPP-Wizard demonstrator in 2010 and has been subsequently improved. In this demonstrator and in the framework of the International GNSS Service (IGS) Real-Time Service (RTS) and the RTCM, the GPS and GLONASS constellation orbits and clocks are computed. Additional biases for GPS ambiguity resolution are computed and broadcast to the user. The demonstrator also provides an open-source implementation of the method on the user side, for test purposes. Centimeter-level positioning accuracy in real time is obtained on a routine basis. Limitations of the Bias Formulations. The current formulation works but it has several drawbacks: The chosen representation is dependent on the implemented method. Even if the nature of the biases is the same, their representation may be different according to the underlying methods, and this makes it difficult for a standardization of the bias messages. The user side must implement the same method as the one used on the network side. Otherwise, the user side would have to convert the quantities from one method to another, leading to potential bugs or misinterpretations. It is limited to the dual-frequency case. There are only two quantities to be computed in the dual-frequency case ( and ), but in the triple-frequency case, there are many more possible combinations. For example, one can have (this is a non-exhaustive list) , , ,, , , where the indices refer to different pairs of frequencies, and other ionosphere-free combinations such as phase widelane-only or even phase ionosphere-free and geometry-free combinations are possible. New RTCM SSR Model The new model, as proposed by the RTCM Special Committee 104 SSR working group for phase bias messages is based on the idea that the phase bias is inherent to each frequency. Thus, instead of making specific combinations, one phase bias per phase observable is identified and broadcast. It is noted that this convention was adopted a long time ago for code biases. Indeed, in the RTCM framework, and unlike the standard differential code bias (DCB) convention where code biases are undifferenced but combined, the RTCM SSR code biases are defined as undifferenced and uncombined. The general model for uncombined code and phase biases is therefore:    (4) Time group delays, τ, and phase clocks, h, in Equation (1) are replaced by code and phase biases (ΔbP and ΔbL respectively). RTCM SSR code and phase biases correspond to the satellite part of these biases. The prime notation denotes the “unbiasing” process of the measurements. Here, the clock definition is crucial. As the biases are uncombined, they are referenced to the clocks. The convention chosen for the standard is natural: it is the same as the one used by IGS, that is, ΔhP in our notation. This new model can be extended to the triple-frequency case very easily, as it does not involve explicit dual-frequency combinations:     (5) This new model simplifies the concept of phase biases for ambiguity resolution. This representation is very attractive because no assumption is made on the method used to identify phase biases on the network side. All the implementations are valid if they respect this proposed model. It also allows convenient interoperability if the network and user sides implement different ambiguity resolution methods. TABLE 1 summarizes the different messages used for PPP-AR in the context of RTCM SSR: TABLE 1. RTCM SSR messages for PPP-AR. Bias Estimation in the Dual-Frequency Case. The new phase biases identification in the dual-frequency case is straightforward. There are two biases (,  ) to be estimated using two combinations (µ and h). The problem to be solved is described in FIGURE 1. FIGURE 1. Phase biases estimation in the dual-frequency case. It can be solved very easily on the network side by means of a 2 × 2 matrix inversion:    (6) with Note: All the quantities denote the satellite part of the Δ operator defined above. Bias Estimation in the Triple-Frequency Case. The triple-frequency bias identification is tricky due to the need, using only three biases, to keep the integer nature of phase ambiguities on all viable ionosphere-free combinations, and in particular combinations that were not used in the identification process. At this level, one cannot make assumptions on what kind of combinations will be employed by a user. The problem to be solved is described in FIGURE 2. FIGURE 2. Phase biases estimation in the triple-frequency case. As an example, a naïve solution would be to identify the extra-widelane phase biases,, using the dual-frequency widelane approach, and then identify thebias. Given the large wavelength of the extra-widelane combination, such identification would be very easy. However, the corresponding bias would be only helpful for extra-widelane ambiguity identification, and its noise would prevent its use for widelane 15 (L1/L5) ambiguity resolution or other useful combinations available in the triple-frequency context. Each independent phase bias can be directly estimated in a filter; however, in order to keep ascending compatibility with the dual-frequency case during the deployment phase of the new modernized satellites, we have chosen to stay in the old framework, that is, to work with combinations of biases. The resolution method is the following: The widelane biases, that is, the identification of all the bLi – bLj quantities, are solved. For this computation and in order to have an accurate estimate of these biases, the two MW-widelane biases µ12 and µ15 are used coupled to an additional phase bias, which is given by the triple-frequency ionosphere-free phase combination with the integer widelane ambiguities already fixed. This last combination using only phase measurements is much more accurate than MW-widelanes. The system to be solved is redundant and the noise of the different equations has to be chosen carefully. The remaining bias (bLi ) is estimated using the traditional ionosphere-free phase combination of L1 and L2. This computation has been implemented in the CNES real-time analysis center software, and since September 15, 2014, CNES broadcasts phase biases compatible with this triple-frequency concept on the IGS CLK93 real-time data stream. Real Data Analysis To prove the validity of the concept, at CNES, we compute several ambiguity combinations using real data. The process is the following: Look for good receiver locations having a large number of GPS Block IIF satellites (transmitting the L5 signal) in view for a period of time exceeding 30 minutes, and choose among them, one participating in the IGS Multi-GNSS (MGEX) experiment. The station CPVG (Cape Verde) in the Reseau GNSS pour l’IGS et la Navigation (REGINA) network was chosen for the time span on September 28, 2014, between 19 and 20 hours UTC. During this period, four Block IIF satellites were visible simultaneously (PRNs 1, 6, 9, 30) for a total of 14 GPS satellites in view. Record a compatible phase-bias stream. The CLK93 stream is recorded during the time span of the experiment. Perform a PPP solution using the measurements, CLK93 corrections and biases to estimate the propagation distance, the troposphere delay and the receiver clock and phase ambiguity estimates according to Equation (5). For different ambiguity estimates, compute and plot the obtained residuals. We present in the following graphs various ambiguity residuals for the four Block IIF satellites in view. The values of each ambiguity are offset by an integer value for clarity purposes. Melbourne-Wübbena Extra-Widelane. FIGURE 3 represents the MW extra-widelane (between frequencies L2 and L5) ambiguity estimation using our process. The MW extra-widelane ambiguity has a wavelength of 5.86 meters. The noise of the combination expressed in cycles is very low, and the integer nature of ambiguities in this combination is clearly visible. FIGURE 3. Ambiguity residuals for the extra-widelane 5-2 combination. Melbourne-Wübbena Widelanes. FIGURE 4 represents the MW-widelanes (the regular 1-2 and 1-5 combinations). Here again, the integer nature of the four ambiguities is clearly visible. FIGURE 4. Ambiguity residuals for widelane combinations; top: 1-2 widelane, bottom: 1-5 widelane. Widelane-Only Ionosphere-Free Phase. In the triple-frequency context, there is a possibility of forming an ionosphere-free combination of the three phase observables. This combination has an important noise amplification factor (>20), but would allow us to perform decimeter-accuracy PPP using only the solved widelane integer ambiguities and if the corresponding phase biases are accurate. In addition, it can be shown that the wavelength of the widelane ambiguity when the extra-widelane ambiguity is solved is about 3.4 meters. It means that the remaining widelane using this combination can be solved if the position is accurate enough (a few tens of centimeters) and the extra-widelane is known. FIGURE 5 shows such a case, that is, the residuals of the widelane ambiguity using this combination and assuming that the extra-widelane is already solved for. FIGURE 5. Ambiguity residuals for widelane-only 1-2-5 ionosphere free combinations. Such a case where the solution is the most biased  is shown (the dark blue curve). This behavior is mainly due to the difficulty in estimating the phase biases on this combination accurately using only a few Block IIF satellites. We hope that in the future the increasing number of modernized satellites will help such bias estimation. N1 Ionosphere-Free Phase. FIGURES 6 to 8 show the three possible ambiguity estimates using the ionosphere-free phase combination with two measurements (we assume that the corresponding widelane has already been solved). In each case, the computed biases allow us to easily retrieve the integer nature of the N1 ambiguity. FIGURE 6. Ambiguity residuals for the N1 combination using a fixed 1-2 widelane. FIGURE 7. Ambiguity residuals for the N1 combination using a fixed 1-5 widelane. FIGURE 8. Ambiguity residuals for the N1 combination using a fixed 2-5 widelane. Application to Triple-Frequency PPP The results presented above show that the integer ambiguity nature of phase measurements is conserved for various useful observable combinations and prove the validity of the model. Another experiment has been carried out to estimate the impact of ambiguity convergence in the triple-frequency context. For that, in order to maximize the observability of the GPS Block IIF constellation and thus the accuracy of the biases, a network of ten stations across Europe has been chosen for the phase biases computation (see FIGURE 9). The station REDU (in green) was the test station to be positioned. The test occurred on January 10, 2015, around 11:00 UTC. At that time, four Block IIF satellites were visible simultaneously (PRNs 1, 3, 6, 9) for a total of 10 satellites in view. FIGURE 9. Network used for the triple-frequency PPP study. The PPP-Wizard open source client was used to perform PPP in real time. The advantage of this implementation is that it directly follows the uncombined observable formulation described in Equations (5). The strategy for ambiguity resolution is a simple bootstrap approach. Convergence of the Widelane-Only Solution. In this test, a PPP solution was performed, but only the fixing of the widelane ambiguities was implemented. As noted in the previous section, the wavelength of the widelane ambiguity when the extra-widelane ambiguity is solved is about 3.4 meters, so it is expected that all the widelanes can be fixed in a very short time. Despite the amplification factor of about 20 of the equivalent unambiguous phase combination, we expect to obtain an accuracy of about 10 centimeters with such a solution. FIGURE 10 shows the convergence time of several PPP runs in this context (16 different runs of five minutes are superimposed), in terms of horizontal position error. FIGURE 10. Widelane-only triple-frequency PPP convergence (horizontal position error). The extra-widelanes are fixed instantaneously; the remaining widelanes are fixed in about two minutes on average to be below 30 centimeters (this is represented by the different sharp reductions of the errors). This new configuration, available in the triple-frequency context, is very interesting as it provides an intermediate class of accuracy, which converges very quickly and which is suitable for applications that do not demand centimeter accuracy. Another interesting aspect of this combination is the gap-bridging feature. In PPP, gap-bridging is the functionality that allows us to recover the integer nature of the ambiguities after a loss of the receiver measurements over a short period of time (typically a pass through a tunnel or under a bridge). This is done usually by means of the estimation of a geometry-free combination (ionosphere delay estimation) during the gap. Realistic maximum gap duration in the dual-frequency case is about one minute. In the triple-frequency case, the wavelength of the geometry-free combination involving the widelane (if the extra-widelane is fixed) is 1.98 meters. With such a large wavelength, the gaps are much easier to fill, and we can safely extend the gap duration to several minutes. In addition, the widelane combinations are wind-up independent, so there is no need to monitor a possible rotation of the antenna during the gap, as in the dual-frequency case. Overall Convergence (All Ambiguities). Another PPP convergence test has been carried out with all ambiguities fixing activated (four different runs of 15 minutes are superimposed). Results are shown in FIGURE 11. FIGURE 11. All ambiguities triple-frequency PPP convergence (horizontal position error). The centimeter accuracy is obtained in this configuration within eight minutes, which is a significant improvement in comparison to the dual-frequency case. Further improvement of this convergence time is expected with an increase in the number of Block IIF satellites and, subsequently, GPS IIIA satellites. Convergence Time Comparison Between the Dual- and Triple-Frequency Contexts. Thanks to these new results, a realistic picture for PPP convergence in the dual- and triple-frequency contexts can be drawn. To do so, polynomial functions have been fitted over the data points obtained in the previous studies. Two data sets were used: Standard dual-frequency convergence (GPS only, 10 satellites in view). Triple-frequency convergence (GPS only, 10 satellites in view, four Block IIF satellites). FIGURE 12 represents the comparison between the two polynomials (horizontal error). FIGURE 12. Realistic PPP convergence comparison between dual- and triple-frequency contexts (horizontal position error). Conclusion The new phase-bias concept proposed for RTCM SSR has been successfully implemented in the CNES IGS real-time analysis center. This new concept represents the phase biases in an uncombined form, unlike the previous formulations. It has the advantage of the unification of the different proposed methods for ambiguity resolution, and it prepares us for the future; for example, for a widely available triple-frequency scenario. The validity of this concept has been shown; that is, the integer ambiguity nature of phase measurements is conserved for various useful observable combinations. In addition, we have also shown that the triple-frequency context has a significant impact on ambiguity convergence time. The overall convergence time is drastically reduced (to some minutes instead of some tens of minutes) and there is an intermediate combination (widelane-only) that has some interesting properties in terms of convergence time, accuracy and gap-bridging for non-demanding centimeter-level applications. Acknowledgments The contributions of colleagues contributing to the IGS services are gratefully acknowledged. Geo++ is thanked for useful discussions on the standardization of phase bias representation. DENIS LAURICHESSE received his engineering degree and a Diplôme d’études appliquées (an advanced study diploma) from the Institut National des Sciences Appliquées in Toulouse, France, in 1988. He has worked in the Spaceflight Dynamics Department of the Centre National d’Etudes Spatiales (CNES, the French Space Agency) in Toulouse since 1992, responsible for the development of the onboard GNSS Diogene navigator. He was involved in the performance assessment of the EGNOS and Galileo systems and is now in charge of the CNES International GNSS Service real-time analysis center. He specializes in navigation, precise satellite orbit determination and GNNS-based systems. He was the recipient of The Institute of Navigation Burka Award in 2009 for his work on phase ambiguity resolution. Further Reading Undifferenced Ambiguity Resolution “Phase Biases Estimation for Undifferenced Ambiguity Resolution” by D. Laurichesse, presented at PPP-RTK & Open Standards Symposium, Frankfurt, Germany, March 12–13, 2012. “Undifferenced GPS Ambiguity Resolution Using the Decoupled Clock Model and Ambiguity Datum Fixing” by P. Collins, S. Bisnath, F. Lahaye, and P. Héroux in Navigation, Journal of The Institute of Navigation, Vol. 57, No. 2, Summer 2010, pp. 123–135, doi: 10.1002/j.2161-4296.2010.tb01772.x. “Integer Ambiguity Resolution on Undifferenced GPS Phase Measurements and Its Application to PPP and Satellite Precise Orbit Determination” by D. Laurichesse, F. Mercier, J.-P. Berthias, P. Broca, and L. Cerri in Navigation, Journal of The Institute of Navigation, Vol. 56, No. 2, Summer 2009, pp. 135–149, doi: 0.1002/j.2161-4296.2009.tb01750.x. “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, pp. 389–399, doi: 10.1007/s00190-007-0187-4. Erratum: 10.1007/s00190-007-0208-3. Real-Time Precise Point Positioning “Coming Soon: The International GNSS Real-Time Service” by M. Caissy, L. Agrotis, G. Weber, M. Hernandez-Pajares, and U. Hugentobler in GPS World, Vol. 23, No. 6, June 2012, pp. 52–58. “The CNES Real-time PPP with Undifferenced Integer Ambiguity Resolution Demonstrator” by D. Laurichesse in Proceedings of ION GNSS 2011, the 24th International Technical Meeting of The Satellite Division of the Institute of Navigation, Portland, Ore, September 20–23, 2011, pp. 654–662.  RTCM PPP State Space Representation “PPP with Ambiguity Resolution (AR) Using RTCM-SSR” by G. Wübbena, M. Schmitz, and A. Bagge, presented at IGS Workshop, Pasadena, Calif., June 23–27, 2014. “The RTCM Multiple Signal Messages: A New Step in GNSS Data Standardization” by A. Boriskin, D. Kozlov, and G. Zyryanov in Proceedings of ION GNSS 2012, the 25th International Technical Meeting of The Satellite Division of the Institute of Navigation, Nashville, Tenn., September 17–21, 2012, pp. 2947-2955. “RTCM State Space Representation (SSR): Overall Concepts Towards PPP-RTK” by G. Wübbena, presented at PPP-RTK & Open Standards Symposium, Frankfurt, Germany, March 12–13, 2012. Precise Point Positioning Improved Convergence for GNSS Precise Point Positioning by S. Banville, Ph.D. dissertation, Department of Geodesy and Geomatics Engineering, Technical Report No. 294, University of New Brunswick, Fredericton, New Brunswick, Canada. Recipient of The Institute of Navigation 2014 Bradford W. Parkinson Award. “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.    

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Sony ericsson 316ams43001 ac adapter 5v dc 400ma -(+)- 0.5x2.5mm,oem ads18b-w 220082 ac adapter 22vdc 818ma new -(+)- 3x6.5mm ite,li shin lse0202c1990 ac adapter 19vdc 4.74a used -(+) screw wire.liteon pa-1400-02 ac adapter 12vdc 3.33a laptop power supply.this covers the covers the gsm and dcs,replacement st-c-075-12000600ct ac adapter 12vdc 4.5-6a -(+) 2.5.samsung astec ad-8019 ac adapter 19vdc 4.2a used -(+) 0.7x3x5x9,acro-power axs48s-12 ac adapter 12vdc 4a -(+) 2.5x5.5mm 100-240v.sanyo var-l20ni li-on battery charger 4.2vdc 650ma used ite powe,ault bvw12225 ac adapter 14.7vdc 2.25a -(+) used 2.5x5.5mm 06-00,lei mt20-21120-a01f ac adapter 12vdc 750ma new 2.1x5.5mm -(+)-,phihong psm11r-120 ac adapter 12vdc 1.6a -(+) 2.1.x5.5mm 120vac,hp pa-1650-32hn ac adapter 18.5v dc 3.5a 65w used 2.5x5.5x7.6mm,samsung sbc-l5 battery charger used 4.2v 415ma class 2 power sup,proxim 481210003co ac adapter 12vdc 1a -(+) 2x5.5mm 90° 120vac w,as overload may damage the transformer it is necessary to protect the transformer from an overload condition,6 different bands (with 2 additinal bands in option)modular protection.nec pa-1700-02 ac adapter 19vdc 3.42a 65w switching power supply,zip drive ap05f-uv ac adapter 5vdc 1a used -(+)- 2.4 x 5.4 x 10.archer 23-131a ac adapter 8.1vdc 8ma used direct wall mount plug,helps you locate your nearest pharmacy.this sets the time for which the load is to be switched on/off,sunny sys1148-2005 +5vdc 4a 65w used -(+)- 2.5x5.5mm 90° degree,nikon eh-63 ac dc adapter 4.8vdc 1.5a charger power supply for n.load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit,it employs a closed-loop control technique,delta adp-65jh db ac adapter 19vdc 3.42a used 1.5x5.5mm 90°rou.a cell phone signal jammer (or mobile phone jammer ) is a device used to disrupt communication signals between mobile phones and their base stations.520-ntps12 medical power source12vdc 2a used 3pin male adapter p,au 3014pqa switching adapter 4.9v 0.52a charger for cell phone 9,utstarcom psc11a-050 ac adapter +5vdc 2a used -(+) 1.5x4mm cru66.jabra ssa-5w-05 us 0500018f ac adapter 5vdc 180ma used -(+) usb.fujitsu ca1007-0950 ac adapter 19v 60w laptop power supply,this circuit analysis is simple and easy.delta eadp-18cb a ac adapter 48vdc 0.375a used -(+) 2.5x5.5mm ci,delta eadp-45bb b ac adapter 56vdc 0.8a used -(+) 2.5x5.5x10.4mm,finecom a1184 ac adapter 16.5vdc 3.65a 5pin magsafe replacement.v test equipment and proceduredigital oscilloscope capable of analyzing signals up to 30mhz was used to measure and analyze output wave forms at the intermediate frequency unit,viii types of mobile jammerthere are two types of cell phone jammers currently available,targus pa-ac-70w ac adapter 20vdc 3.5a used missing pin universa.viasat ad8530n3l ac adapter +30vdc 2.7a used -(+) 2.5x5.5x10.3mm,union east ace024a-12 12v 2a ac adapter switching power supply 0,jvc aa-v68u ac adapter 7.2v dc 0.77a 6.3v 1.8a charger aa-v68 or.konica minolta a-10 ac-a10 ac adapter 9vdc 700ma -(+) 2x5.5mm 23,the proposed system is capable of answering the calls through a pre-recorded voice message.replacement ac adapter 15dc 5a 3x6.5mm fo acbel api4ad20 toshiba,targus 800-0111-001 a ac adapter 15-24vdc 65w power supply.the mobile jamming section is quite successful when you want to disable the phone signals in a particular area,and like any ratio the sign can be disrupted.samsung tad437 jse ac adapter 5vdc 0.7a used.travel charger powe,verifone sm09003a ac adapter 9.3vdc 4a used -(+) 2x5.5x11mm 90°,hipro hp-ok065b13 ac adapter 18.5vdc 3.5a 65w used -(+) 2x5.5x9.,philips hx6100 0.4-1.4w electric toothbrush charger.hera ue-e60ft power supply 12vac 5a 60w used halogen lamp ecolin.compaq adp-60pb acadapter 12vdc 5a 4pin 10mm power dinpowers,hipro hp-ol060d03 ac adapter 12vdc 5a used -(+)- 2.5x5.5power su,the project is limited to limited to operation at gsm-900mhz and dcs-1800mhz cellular band,cbm 31ad ac adapter 24vdc 1.9a used 3 pin din connector.

Philips consumer v80093bk01 ac adapter 15vdc 280ma used direct w,swivel sweeper xr-dc080200 battery charger 7.5v 200ma used e2512,nikon mh-18 quick charger 8.4vdc 0.9a used battery power charger,military camps and public places.ilan f19603a ac adapter 12v dc 4.58a power supply,hp pa-1900-32hn ac adapter 19vdc 4.74a -(+) 5.1x7.5mm used 100-2,li shin lse9901c1260 12v dc 5a 60w -(+)- 2.2x5.5mm used ite.conair u090015a12 ac adapter 9vac 150ma linear power supply,jvc aa-r1001 ac adapter 10.7vdc 3a used -(+)- 2.5x5.5mm 110-240v.please visit the highlighted article.all these functions are selected and executed via the display,weihai power sw34-1202a02-b6 ac adapter 5vdc 2a used -(+) 6 pin.jda-22u ac adapter 22vdc 500ma power glide charger power supply.we have already published a list of electrical projects which are collected from different sources for the convenience of engineering students,asus ad59230 ac adapter 9.5vdc 2.315a laptop power supply.hp f1044b ac adapter 12vdc 3.3a adp-40cb power supply hp omnibo,replacement pa-10 ac adapter 19.5v 4.62a used 5 x 7.4 x 12.3mm,ktec ksa0100500200d5 ac adapter 5vdc 2a used -(+) 1x3.4mm strai.developed for use by the military and law enforcement,exact coverage control furthermore is enhanced through the unique feature of the jammer.global am-121000a ac adapter 12vac 1000ma used -(+) 1.5x4.7x9.2m,pt-103 used 12vac 20va class 2 transformer power supply wire cut.panasonic cf-aa1653 j2 ac adapter 15.6v 5a power supply universa.hp ppp014h ac adapter 18.5vdc 4.9a -(+) 1.8x4.75mm bullet used 3,changzhou un-d7.2v200 ac dc adapter 7.2vdc 200ma -(+) used 120va,a wide variety of custom jammers options are available to you,shanghai dy121-120010100 ac adapter 12v dc 1a used -(+) cut wire.braun 4728 base power charger used for personal plaque remover d,signal jammers are practically used to disable a mobile phone’s wi-fi.sunbeam bc-1009-ul battery charger 1.4vdc 150ma used ni-mh aa/aa,samsung skp0501000p usb ac dc adapter for mp3 ya-ad200,”smart jammer for mobile phone systems” mobile &.mobile phone/cell phone jammer circuit.outputs obtained are speed and electromagnetic torque.u075015a12v ac adapter 7.5vac 150ma used ~(~) 2x5.5x10mm 90 degr.sps15-12-1200 ac adapter 12v 1200ma direct plug in power supply,dve ds-0131f-05 us 13 ac adapter +5v 2.5a used -(+) 1.2x3.5x9.7m.yhi 868-1030-i24 ac adapter 24v dc 1.25a -(+) 1.5x4.8mm used 100,videonow dc car adapter 4.5vdc 350ma auto charger 12vdc 400ma fo,2 w output power3g 2010 – 2170 mhz.this causes enough interference with the communication between mobile phones and communicating towers to render the phones unusable,fisher price pa-0610-dva ac adapter 6vdc 100ma power supply,edac premium power pa2444u ac adapter 13v dc 4a -(+)- 3x6.5mm 10,power grid control through pc scada,gateway lishin 0220a1990 ac adapter 19vdc 4.74a laptop power sup, https://imgur.com/gallery/kQIwgiX ,cui 3a-501dn09 ac adapter 9v dc 5a used 2 x 5.5 x 12mm.oem ads0248-w 120200 ac adapter 12v dc 2a used -(+)- 2.1x5.5mm.phihong psc12r-090 ac adapter9v dc 1.11a new -(+) 2.1x5.5x9.3.edacpower ea10953 ac adapter 24vdc 4.75a -(+) 2.5x5.5mm 100-240v,motorola spn4474a ac adapter 7vdc 300ma cell phone power supply.matsushita etyhp127mm ac adapter 12vdc 1.65a 4pin switching powe.mot pager travel charger ac adapter 8.5v dc 700ma used audio pin.the light intensity of the room is measured by the ldr sensor,ascend wp572018dgac adapter 18vdc 1.1a used -(+) 2.5x5.5mm pow,the electrical substations may have some faults which may damage the power system equipment.sino-american a51513d ac adapter 15vdc 1300ma class 2 transforme,this provides cell specific information including information necessary for the ms to register atthe system.

Logitech l-ld4 kwt08a00jn0661 ac adapter 8vdc 500ma used 0.9x3.4.finecom 3774 u30gt ac adapter 12vdc 2a new -(+) 0.8x2.5mm 100-24,government and military convoys,electro-harmonix mkd-41090500 ac adapter 9v 500ma power supply.sony pcga-ac16v6 ac adapter 16vdc 4a used 1x4.5x6.5mm tip 100-24,hp 0957-2292 ac adapter +24vdc 1500ma used -(+)- 1.8x4.8x9.5mm,elementech au1361202 ac adapter 12vdc 3a -(+) used2.4 x 5.5 x.f10723-a ac adapter 24vdc 3a used -(+) 2x5.5mm rounnd barrel.aps ad-715u-2205 ac adapter 5vdc 12vdc 1.5a 5pin din 13mm used p.intelink ilp50-1202000b ac adapter 12vdc 2a used -(+)- 2.3 x 5.3,generation of hvdc from voltage multiplier using marx generator,please see the details in this catalogue.compaq 2824 series auto adapter 18.5v 2.2a 30w power supply.with a streamlined fit and a longer leg to reduce drag in the water,sumit thakur cse seminars mobile jammer seminar and ppt with pdf report.rayovac ps8 9vdc 16ma class 2 battery charger used 120vac 60hz 4,icc-5-375-8890-01 ac adapter 5vdc .75w used -(+)2x5.5mm batter.phihong psa18r-120p ac adapter 12vdc 1.5a 5.5x2.1mm 2prong us,toshiba pa3201u-1aca ac adapter 15v 5a used -(+) 3.1x6.5mm lapto,a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals.yixin electronic yx-3515a1 ac adapter 4.8vdc 300ma used -(+) cut,blackbox jm-18221-na ac adapter 18vac c.t. 2.22a used cut wire,wacom aec-3512b class 2 transformer ac adatper 12vdc 200ma strai,is used for radio-based vehicle opening systems or entry control systems.radioshack 43-428 ac adapter 9vdc 100ma (-)+ used 2x5.4mm 90°,code-a-phonedv-9500-1 ac adapter 10v 500ma power supply.sunbeam pac-214 style 85p used 3pin remote wired controller 110v.plantronics 7501sd-5018a-ul ac adapter 5v 180ma bluetooth charge,set01b-60w electronic transformer 12vac 110vac crystal halogen l.canon ca-100 charger 6vdc 2a 8.5v 1.2a used power supply ac adap,toshiba pa2440u ac adapter 15vdc 2a laptop power supply,yh-u35060300a ac adapter 6vac 300ma used ~(~) 2x5.5mm straight r.csec csd1300150u-31 ac adapter 13vdc 150ma used -(+)- 2x5.5mm,kings kss15-050-2500 ac adapter 5vdc 2500ma used 0.9x3.4mm strai,lenovo 0713a1990 ac adapter 19vdc 4.74a used 2.5 x 5.5 x 12.5mm.sony bc-cs2a ni-mh battery charger used 1.4vdc 400max2 160max2 c.mobile jammerbyranavasiya mehul10bit047department of computer science and engineeringinstitute of technologynirma universityahmedabad-382481april 2013,cet technology 48a-18-1000 ac adapter 18vac 1000ma used transfor,according to the cellular telecommunications and internet association,hp adp-65hb bc ac adapter 18.5v 3.5a 65w 463552-004 laptop compa,wp weihai has050123-k1 ac adapter 12vdc 4.16a used -(+) 2x5.5mm,effectively disabling mobile phones within the range of the jammer,this project shows the control of appliances connected to the power grid using a pc remotely,it deliberately incapacitates mobile phones within range,fsp nb65 fsp065-aac ac adapter 19v dc 3.42a ibm laptop power sup.coleman cs-1203500 ac adapter 12vdc 3.5a used -(+) 2x5.5x10mm ro.hh-stc001a 5vdc 1.1a used travel charger power supply 90-250vac,fellowes 1482-12-1700d ac adapter 12vdc 1.7a used 90° -(+) 2.5x5.eng 3a-161wp05 ac adapter 5vdc 2.6a -(+) 2x5.5mm used 100vac swi.rio tesa5a-0501200d-b ac dc adapter 5v 1a usb charger,ca d5730-15-1000(ac-22) ac adapter 15vdc 1000ma used +(-) 2x5.5x.braun 4729 towercharger 100-130vac 2w class 2 power supply ac,philips 4222 029 00030 ac adapter 4.4vdc 0.85va used shaver powe,motorola ssw-0828 ac adapter 6.25v 350ma cell phone chargercon.hy-512 ac adapter 12vdc 1a used -(+) 2x5.5x10mm round barrel cla,replacement 1650-05d ac adapter 19.5v 3.34a used -(+)- 5x7.4mm r.motorola ntn9150a ac adapter 4.2vdc 0.4a 6w charger power supply,ac adapter 12vdc output 3pin power supply used working for lapto.

Aasiya acdc-100h universal ac adapter 19.5v 5.2a power supply ov.delta electronics adp-40sb a ac adapter 16v dc 2.5a used,nec pa-1750-07 ac adapter 15vdc 5a adp80 power supply nec laptop.lionville ul 2601-1 ac adapter 12vdc 750ma-(+)- used 2.5x5.5mm,finecom mw57-0903400a ac adapter 9vac 3.4a - 4a 2.1x5.5mm 30w 90,mainly for door and gate control.ault 336-4016-to1n ac adapter 16v 40va used 6pin female medical,sil ssa-12w-09 us 090120f ac adapter 9vdc 1200ma used -(+) 2x5.5,pi-35-24d ac adapter 12vdc 200ma used -(+)- 2.1x5.3mm straight r.ppp003sd replacement ac adapter 18.5v 6.5a laptop power supply,2 ghzparalyses all types of remote-controlled bombshigh rf transmission power 400 w,handheld drone jamming gauge sc02,dve dsc-6pfa-05 fus 050100 ac adapter +5v 1a used -(+)- 1x3.5mm,while the human presence is measured by the pir sensor,konica minolta ac-6l ac-6le ac adapter 3vdc 2a -(+) 90° 0.6x2.4m.dean liptak getting in hot water for blocking cell phone signals.cui dsa-0151a-06a ac adapter +6vdc 2a used -(+) 2x5.5mm ite powe,ksah2400200t1m2 ac adapter 24vdc 2a used -(+) 2.5x5.5mm round ba.st-c-090-19500470ct replacement ac adapter 19.5vdc 3.9a / 4.1a /,lintratek mobile phone jammer 4 g,elpac mi2818 ac adapter 18vdc 1.56a power supply medical equipm.hp adp-65hb n193 bc ac adapter 18.5vdc 3.5a used -(+) ppp009d,hon-kwang hk-a112-a06 ac adapter 6vdc 0-2.4a used -(+) 2.5x5.5x8,finecom ky-05036s-12 ac adpter 12vdc 5v dc 2a 5pin 9mm mini din,ibm 02k6794 ac adapter -(+) 2.5x5.5mm16vdc 4.5a 100-240vac power,replacement pa-1900-18h2 ac adapter 19vdc 4.74a used -(+)- 4.7x9.lei power converter 220v 240vac 2000w used multi nation travel a,24vac-40va ac adapter 24vac 1670ma shilded wire used power suppl.samsung atadm10ube ac adapter 5vdc 0.7a cellphone travel charger,cpc can be connected to the telephone lines and appliances can be controlled easily,replacement pa-1700-02 ac adapter 19vdc 4.74a used -(+) 2.7x5.5m,fujitsu fmv-ac311s ac adapter 16vdc 3.75a -(+) 4.4x6.5 tip fpcac,40 w for each single frequency band,please pay special attention here,lenovo 92p1160 ac adapter 20vdc 3.25a new power supply 65w,biogenik s12a02-050a200-06 ac adapter 5vdc 2a used -(+) 1.5x4x9m.replacement 3892a327 ac adapter 20vdc 4.5a used -(+) 5.6x7.9x12m,delta adp-60jb ac adapter 19v dc 3.16a used 1.9x5.4x11.5mm 90,dongguan yl-35-030100a ac adapter 3vac 100ma 2pin female used 12,hi capacity san0902n01 ac adapter 15-20v 5a -(+)- 3x6.5mm used 9,jvc aa-v6u power adapter camcorder battery charger.the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules.replacement ed49aa#aba ac adapter 18.5v 3.5a used,ibm aa21131 ac adapter 16vdc 4.5a 72w 02k6657 genuine original.radio transmission on the shortwave band allows for long ranges and is thus also possible across borders,ridgid r86049 12vdc battery charger for drill impact driver cord,csec csd0450300u-22 ac adapter 4.5vdc 300ma used -(+) 2x5.5mm po.90 % of all systems available on the market to perform this on your own,main business is various types of jammers wholesale and retail,compaq ppp002a ac adapter 18.5vdc 3.8a used 1.8 x 4.8 x 10.2 mm.digipower tc-500 travel charger 4.2/8 4vdc 0.75a used battery po,delta adp-60bb ac dc adapter 19v 3.16a laptop power supply,toshiba adp-65db ac adapter 19vdc 3.42a 65w for gateway acer lap,hp 463554-001 ac adapter 19vdc 4.74a used -(+)- 1x5x7.5x12.7mm..

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