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A Civilian GPS Position Authentication System By Zhefeng Li and Demoz Gebre-Egziabher INNOVATION INSIGHTS by Richard Langley MY UNIVERSITY, the University of New Brunswick, is one of the few institutes of higher learning still using Latin at its graduation exercises. The president and vice-chancellor of the university asks the members of the senate and board of governors present “Placetne vobis Senatores, placetne, Gubernatores, ut hi supplicatores admittantur?” (Is it your pleasure, Senators, is it your pleasure, Governors, that these supplicants be admitted?). In the Oxford tradition, a supplicant is a student who has qualified for their degree but who has not yet been admitted to it. Being a UNB senator, I was familiar with this usage of the word supplicant. But I was a little surprised when I first read a draft of the article in this month’s Innovation column with its use of the word supplicant to describe the status of a GPS receiver. If we look up the definition of supplicant in a dictionary, we find that it is “a person who makes a humble or earnest plea to another, especially to a person in power or authority.” Clearly, that describes our graduating students. But what has it got to do with a GPS receiver? Well, it seems that the word supplicant has been taken up by engineers developing protocols for computer communication networks and with a similar meaning. In this case, a supplicant (a computer or rather some part of its operating system) at one end of a secure local area network seeks authentication to join the network by submitting credentials to the authenticator on the other end. If authentication is successful, the computer is allowed to join the network. The concept of supplicant and authenticator is used, for example, in the IEEE 802.1X standard for port-based network access control. Which brings us to GPS. When a GPS receiver reports its position to a monitoring center using a radio signal of some kind, how do we know that the receiver or its associated communications unit is telling the truth? It’s not that difficult to generate false position reports and mislead the monitoring center into believing the receiver is located elsewhere — unless an authentication procedure is used. In this month’s column, we look at the development of a clever system that uses the concept of supplicant and authenticator to assess the truthfulness of position reports. “Innovation” is a regular feature that discusses advances in GPS technology andits 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. Contact him at lang @ unb.ca. This article deals with the problem of position authentication. The term “position authentication” as discussed in this article is taken to mean the process of checking whether position reports made by a remote user are truthful (Is the user where they say they are?) and accurate (In reality, how close is a remote user to the position they are reporting?). Position authentication will be indispensable to many envisioned civilian applications. For example, in the national airspace of the future, some traffic control services will be based on self-reported positions broadcast via ADS-B by each aircraft. Non-aviation applications where authentication will be required include tamper-free shipment tracking and smart-border systems to enhance cargo inspection procedures at commercial ports of entry. The discussions that follow are the outgrowth of an idea first presented by Sherman Lo and colleagues at Stanford University (see Further Reading). For illustrative purposes, we will focus on the terrestrial application of cargo tracking. Most of the commercial fleet and asset tracking systems available in the market today depend on a GPS receiver installed on the cargo or asset. The GPS receiver provides real-time location (and, optionally, velocity) information. The location and the time when the asset was at a particular location form the tracking message, which is sent back to a monitoring center to verify if the asset is traveling in an expected manner. This method of tracking is depicted graphically in FIGURE 1. FIGURE 1. A typical asset tracking system. The approach shown in Figure 1 has at least two potential scenarios or fault modes, which can lead to erroneous tracking of the asset. The first scenario occurs when an incorrect position solution is calculated as a result of GPS RF signal abnormalities (such as GPS signal spoofing). The second scenario occurs when the correct position solution is calculated but the tracking message is tampered with during the transmission from the asset being tracked to the monitoring center. The first scenario is a falsification of the sensor and the second scenario is a falsification of the transmitted position report. The purpose of this article is to examine the problem of detecting sensor or report falsification at the monitoring center. We discuss an authentication system utilizing the white-noise-like spreading codes of GPS to calculate an authentic position based on a snapshot of raw IF signal from the receiver. Using White Noise as a Watermark The features for GPS position authentication should be very hard to reproduce and unique to different locations and time. In this case, the authentication process is reduced to detecting these features and checking if these features satisfy some time and space constraints. The features are similar to the well-designed watermarks used to detect counterfeit currency. A white-noise process that is superimposed on the GPS signal would be a perfect watermark signal in the sense that it is impossible reproduce and predict. FIGURE 2 is an abstraction that shows how the above idea of a superimposed white-noise process would work in the signal authentication problem. The system has one transmitter, Tx , and two receivers, Rs and Ra. Rs is the supplicant and Ra is the authenticator. The task of the authenticator is to determine whether the supplicant is using a signal from Tx or is being spoofed by a malicious transmitter, Tm. Ra is the trusted source, which gets a copy of the authentic signal, Vx(t) (that is, the signal transmitted by Tx). The snapshot signal, Vs(t), received at Rs is sent to the trusted agent to compare with the signal, Va(t), received at Ra. Every time a verification is performed, the snapshot signal from Rs is compared with a piece of the signal from Ra. If these two pieces of signal match, we can say the snapshot signal from Rs was truly transmitted from Tx. For the white-noise signal, match detection is accomplished via a cross-correlation operation (see Further Reading). The cross-correlation between one white-noise signal and any other signal is always zero. Only when the correlation is between the signal and its copy will the correlation have a non-zero value. So a non-zero correlation means a match. The time when the correlation peak occurs provides additional information about the distance between Ra and Rs. Unfortunately, generation of a white-noise watermark template based on a mathematical model is impossible. But, as we will see, there is an easy-to-use alternative. FIGURE 2. Architecture to detect a snapshot of a white-noise signal. An Intrinsic GPS Watermark The RF carrier broadcast by each GPS satellite is modulated by the coarse/acquisition (C/A) code, which is known and which can be processed by all users, and the encrypted P(Y) code, which can be decoded and used by Department of Defense (DoD) authorized users only. Both civilians and DoD-authorized users see the same signal. To commercial GPS receivers, the P(Y) code appears as uncorrelated noise. Thus, as discussed above, this noise can be used as a watermark, which uniquely encodes locations and times. In a typical civilian GPS receiver’s tracking loop, this watermark signal can be found inside the tracking loop quadrature signal. The position authentication approach discussed here is based on using the P(Y) signal to determine whether a user is utilizing an authentic GPS signal. This method uses a segment of noisy P(Y) signal collected by a trusted user (the authenticator) as a watermark template. Another user’s (the supplicant’s) GPS signal can be compared with the template signal to judge if the user’s position and time reports are authentic. Correlating the supplicant’s signal with the authenticator’s copy of the signal recorded yields a correlation peak, which serves as a watermark. An absent correlation peak means the GPS signal provided by the supplicant is not genuine. A correlation peak that occurs earlier or later than predicted (based on the supplicant’s reported position) indicates a false position report. System Architecture FIGURE 3 is a high-level architecture of our proposed position authentication system. In practice, we need a short snapshot of the raw GPS IF signal from the supplicant. This piece of the signal is the digitalized, down-converted, IF signal before the tracking loops of a generic GPS receiver. Another piece of information needed from the supplicant is the position solution and GPS Time calculated using only the C/A signal. The raw IF signal and the position message are transmitted to the authentication center by any data link (using a cell-phone data network, Wi-Fi, or other means). FIGURE 3. Architecture of position authentication system. The authentication station keeps track of all the common satellites seen by both the authenticator and the supplicant. Every common satellite’s watermark signal is then obtained from the authenticator’s tracking loop. These watermark signals are stored in a signal database. Meanwhile, the pseudorange between the authenticator and every satellite is also calculated and is stored in the same database. When the authentication station receives the data from the supplicant, it converts the raw IF signal into the quadrature (Q) channel signals. Then the supplicant’s Q channel signal is used to perform the cross-correlation with the watermark signal in the database. If the correlation peak is found at the expected time, the supplicant’s signal passes the signal-authentication test. By measuring the relative peak time of every common satellite, a position can be computed. The position authentication involves comparing the reported position of the supplicant to this calculated position. If the difference between two positions is within a pre-determined range, the reported position passes the position authentication. While in principle it is straightforward to do authentication as described above, in practice there are some challenges that need to be addressed. For example, when there is only one common satellite, the only common signal in the Q channel signals is this common satellite’s P(Y) signal. So the cross-correlation only has one peak. If there are two or more common satellites, the common signals in the Q channel signals include not only the P(Y) signals but also C/A signals. Then the cross-correlation result will have multiple peaks. We call this problem the C/A leakage problem, which will be addressed below. C/A Residual Filter The C/A signal energy in the GPS signal is about double the P(Y) signal energy. So the C/A false peaks are higher than the true peak. The C/A false peaks repeat every 1 millisecond. If the C/A false peaks occur, they are greater than the true peak in both number and strength. Because of background noise, it is hard to identify the true peak from the correlation result corrupted by the C/A residuals. To deal with this problem, a high-pass filter can be used. Alternatively, because the C/A code is known, a match filter can be designed to filter out any given GPS satellite’s C/A signal from the Q channel signal used for detection. However, this implies that one match filter is needed for every common satellite simultaneously in view of the authenticator and supplicant. This can be cumbersome and, thus, the filtering approach is pursued here. In the frequency domain, the energy of the base-band C/A signal is mainly (56 percent) within a ±1.023 MHz band, while the energy of the base-band P(Y) signal is spread over a wider band of ±10.23 MHz. A high-pass filter can be applied to Q channel signals to filter out the signal energy in the ±1.023 MHz band. In this way, all satellites’ C/A signal energy can be attenuated by one filter rather than using separate match filters for different satellites. FIGURE 4 is the frequency response of a high-pass filter designed to filter out the C/A signal energy. The spectrum of the C/A signal is also plotted in the figure. The high-pass filter only removes the main lobe of the C/A signals. Unfortunately, the high-pass filter also attenuates part of the P(Y) signal energy. This degrades the auto-correlation peak of the P(Y) signal. Even though the gain of the high-pass filter is the same for both the C/A and the P(Y) signals, this effect on their auto-correlation is different. That is because the percentage of the low-frequency energy of the C/A signal is much higher than that of the P(Y) signal. This, however, is not a significant drawback as it may appear initially. To see why this is so, note that the objective of the high-pass filter is to obtain the greatest false-peak rejection ratio defined to be the ratio between the peak value of P(Y) auto-correlation and that of the C/A auto-correlation. The false-peak rejection ratio of the non-filtered signals is 0.5. Therefore, all one has to do is adjust the cut-off frequency of the high-pass filter to achieve a desired false-peak rejection ratio. FIGURE 4. Frequency response of the notch filter. The simulation results in FIGURE 5 show that one simple high-pass filter rather than multiple match filters can be designed to achieve an acceptable false-peak rejection ratio. The auto-correlation peak value of the filtered C/A signal and that of the filtered P(Y) signal is plotted in the figure. While the P(Y) signal is attenuated by about 25 percent, the C/A code signal is attenuated by 91.5 percent (the non-filtered C/A auto-correlation peak is 2). The false-peak rejection ratio is boosted from 0.5 to 4.36 by using the appropriate high-pass filter. FIGURE 5. Auto-correlation of the filtered C/A and P(Y) signals. Position Calculation Consider the situation depicted in FIGURE 6 where the authenticator and the supplicant have multiple common satellites in view. In this case, not only can we perform the signal authentication but also obtain an estimate of the pseudorange information from the authentication. Thus, the authenticated pseudorange information can be further used to calculate the supplicant’s position if we have at least three estimates of pseudoranges between the supplicant and GPS satellites. Since this position solution of the supplicant is based on the P(Y) watermark signal rather than the supplicant’s C/A signal, it is an independent and authentic solution of the supplicant’s position. By comparing this authentic position with the reported position of the supplicant, we can authenticate the veracity of the supplicant’s reported GPS position. FIGURE 6. Positioning using a watermark signal. The situation shown in Figure 6 is very similar to double-difference differential GPS. The major difference between what is shown in the figure and the traditional double difference is how the differential ranges are calculated. Figure 6 shows how the range information can be obtained during the signal authentication process. Let us assume that the authenticator and the supplicant have four common GPS satellites in view: SAT1, SAT2, SAT3, and SAT4. The signals transmitted from the satellites at time t are S1(t), S2(t), S3(t), and S4(t), respectively. Suppose a signal broadcast by SAT1 at time t0 arrives at the supplicant at t0 + ν1s where ν1s is the travel time of the signal. At the same time, signals from SAT2, SAT3, and SAT4 are received by the supplicant. Let us denote the travel time of these signals as ν2s, ν3s, and ν4s, respectively. These same signals will be also received at the authenticator. We will denote the travel times for the signals from satellite to authenticator as ν1a, ν2a, ν3a, and ν4a. The signal at a receiver’s antenna is the superposition of the signals from all the satellites. This is shown in FIGURE 7 where a snapshot of the signal received at the supplicant’s antenna at time t0 + ν1s includes GPS signals from SAT1, SAT2, SAT3, and SAT4. Note that even though the arrival times of these signals are the same, their transmit times (that is, the times they were broadcast from the satellites) are different because the ranges are different. The signals received at the supplicant will be S1(t0), S2(t0 + ν1s – ν2s), S3(t0 + ν1s – ν3s), and S4(t0 + ν1s – ν4s). This same snapshot of the signals at the supplicant is used to detect the matched watermark signals from SAT1, SAT2, SAT3, and SAT4 at the authenticator. Thus the correlation peaks between the supplicant’s and the authenticator’s signal should occur at t0 + ν1a, t0 + ν1s – ν2s + ν2a, t0 + ν1s – ν3s + ν3a, and t0 + ν1s – ν4s + ν4a. Referring to Figure 6 again, suppose the authenticator’s position (xa, ya, za) is known but the supplicant’s position (xs, ys, zs) is unknown and needs to be determined. Because the actual ith common satellite (xi , yi , zi ) is also known to the authenticator, each of the ρia, the pseudorange between the ith satellite and the authenticator, is known. If ρis is the pseudorange to the ith satellite measured at the supplicant, the pseudoranges and the time difference satisfies equation (1): ρ2s – ρ1s= ρ2a – ρ1a – ct21 + cχ21      (1) where χ21 is the differential range error primarily due to tropospheric and ionospheric delays. In addition, c is the speed of light, and t21 is the measured time difference as shown in Figure 7. Finally, ρis for i = 1, 2, 3, 4 is given by:   (2) FIGURE 7. Relative time delays constrained by positions. If more than four common satellites are in view between the supplicant and authenticator, equation (1) can be used to form a system of equations in three unknowns. The unknowns are the components of the supplicant’s position vector rs = [xs, ys, zs]T. This equation can be linearized and then solved using least-squares techniques. When linearized, the equations have the following form: Aδrs= δm       (3) where δrs = [δxs,δys,δzs]T, which is the estimation error of the supplicant’s position. The matrix A is given by where  is the line of sight vector from the supplicant to the ith satellite. Finally, the vector δm is given by: (4) where δri is the ith satellite’s position error, δρia is the measurement error of pseudorange ρia or pseudorange noise. In addition, δtij is the time difference error. Finally, δχij is the error of χij defined earlier. Equation (3) is in a standard form that can be solved by a weighted least-squares method. The solution is δrs = ( AT R-1 A)-1 AT R-1δm     (5) where R is the covariance matrix of the measurement error vector δm. From equations (3) and (5), we can see that the supplicant’s position accuracy depends on both the geometry and the measurement errors. Hardware and Software In what follows, we describe an authenticator which is designed to capture the GPS raw signals and to test the performance of the authentication method described above. Since we are relying on the P(Y) signal for authentication, the GPS receivers used must have an RF front end with at least a 20-MHz bandwidth. Furthermore, they must be coupled with a GPS antenna with a similar bandwidth. The RF front end must also have low noise. This is because the authentication method uses a noisy piece of the P(Y) signal at the authenticator as a template to detect if that P(Y) piece exists in the supplicant’s raw IF signal. Thus, the detection is very sensitive to the noise in both the authenticator and the supplicant signals. Finally, the sampling of the down-converted and digitized RF signal must be done at a high rate because the positioning accuracy depends on the accuracy of the pseudorange reconstructed by the authenticator. The pseudorange is calculated from the time-difference measurement. The accuracy of this time difference depends on the sampling frequency to digitize the IF signal. The high sampling frequency means high data bandwidth after the sampling. The authenticator designed for this work and shown in FIGURE 8 satisfies the above requirements. A block diagram of the authenticator is shown in Figure 8a and the constructed unit in Figure 8b. The IF signal processing unit in the authenticator is based on the USRP N210 software-defined radio. It offers the function of down converting, digitalization, and data transmission. The firmware and field-programmable-gate-array configuration in the USRP N210 are modified to integrate a software automatic gain control and to increase the data transmission efficiency. The sampling frequency is 100 MHz and the effective resolution of the analog-to-digital conversion is 6 bits. The authenticator is battery powered and can operate for up to four hours at full load. FIGURE 8a. Block diagram of GPS position authenticator. Performance Validation Next, we present results demonstrating the performance of the authenticator described above. First, we present results that show we can successfully deal with the C/A leakage problem using the simple high-pass filter. We do this by performing a correlation between snapshots of signal collected from the authenticator and a second USRP N210 software-defined radio. FIGURE 9a is the correlation result without the high-pass filter. The periodic peaks in the result have a period of 1 millisecond and are a graphic representation of the C/A leakage problem. Because of noise, these peaks do not have the same amplitude. FIGURE 9b shows the correlation result using the same data snapshot as in Figure 9a. The difference is that Figure 9b uses the high-pass filter to attenuate the false peaks caused by the C/A signal residual. Only one peak appears in this result as expected and, thus, confirms the analysis given earlier. FIGURE 9a. Example of cross-correlation detection results without high-pass filter. FIGURE 9b. Example of cross-correlation with high-pass filter. We performed an experiment to validate the authentication performance. In this experiment, the authenticator and the supplicant were separated by about 1 mile (about 1.6 kilometers). The location of the authenticator was fixed. The supplicant was then sequentially placed at five points along a straight line. The distance between two adjacent points is about 15 meters. The supplicant was in an open area with no tall buildings or structures. Therefore, a sufficient number of satellites were in view and multipath, if any, was minimal. The locations of the five test points are shown in FIGURE 10. FIGURE 10. Five-point field test. Image courtesy of Google. The first step of this test was to place the supplicant at point A and collect a 40-millisecond snippet of data. This data was then processed by the authenticator to determine if: The signal contained the watermark. We call this the “signal authentication test.” It determines whether a genuine GPS signal is being used to form the supplicant’s position report. The supplicant is actually at the position coordinates that they say they are. We call this the “position authentication test.” It determines whether or not falsification of the position report is being attempted. Next, the supplicant was moved to point B. However, in this instance, the supplicant reports that it is still located at point A. That is, it makes a false position report. This is repeated for the remaining positions (C through E) where at each point the supplicant reports that it is located at point A. That is, the supplicant continues to make false position reports. In this experiment, we have five common satellites between the supplicant (at all of the test points A to E) and the authenticator. The results of the experiment are summarized in TABLE 1. If we can detect a strong peak for every common satellite, we say this point passes the signal authentication test (and note “Yes” in second column of Table 1). That means the supplicant’s raw IF signal has the watermark signal from every common satellite. Next, we perform the position authentication test. This test tries to determine whether the supplicant is at the position it claims to be. If we determine that the position of the supplicant is inconsistent with its reported position, we say that the supplicant has failed the position authentication test. In this case we put a “No” in the third column of Table 1. As we can see from Table 1, the performance of the authenticator is consistent with the test setup. That is, even though the wrong positions of points (B, C, D, E) are reported, the authenticator can detect the inconsistency between the reported position and the raw IF data. Furthermore, since the distance between two adjacent points is 15 meters, this implies that resolution of the position authentication is at or better than 15 meters. While we have not tested it, based on the timing resolution used in the system, we believe resolutions better than 12 meters are achievable. Table 1. Five-point position authentication results. Conclusion In this article, we have described a GPS position authentication system. The authentication system has many potential applications where high credibility of a position report is required, such as cargo and asset tracking. The system detects a specific watermark signal in the broadcast GPS signal to judge if a receiver is using the authentic GPS signal. The differences between the watermark signal travel times are constrained by the positions of the GPS satellites and the receiver. A method to calculate an authentic position using this constraint is discussed and is the basis for the position authentication function of the system. A hardware platform that accomplishes this was developed using a software-defined radio. Experimental results demonstrate that this authentication methodology is sound and has a resolution of better than 15 meters. This method can also be used with other GNSS systems provided that watermark signals can be found. For example, in the Galileo system, the encrypted Public Regulated Service signal is a candidate for a watermark signal. In closing, we note that before any system such as ours is fielded, its performance with respect to metrics such as false alarm rates (How often do we flag an authentic position report as false?) and missed detection probabilities (How often do we fail to detect false position reports?) must be quantified. Thus, more analysis and experimental validation is required. Acknowledgments The authors acknowledge the United States Department of Homeland Security (DHS) for supporting the work reported in this article through the National Center for Border Security and Immigration under grant number 2008-ST-061-BS0002. However, any opinions, findings, conclusions or recommendations in this article are those of the authors and do not necessarily reflect views of the DHS. This article is based on the paper “Performance Analysis of a Civilian GPS Position Authentication System” presented at PLANS 2012, the Institute of Electrical and Electronics Engineers / Institute of Navigation Position, Location and Navigation Symposium held in Myrtle Beach, South Carolina, April 23–26, 2012. Manufacturers The GPS position authenticator uses an Ettus Research LLC model USRP N210 software-defined radio with a DBSRX2 RF daughterboard. Zhefeng Li is a Ph.D. candidate in the Department of Aerospace Engineering and Mechanics at the University of Minnesota, Twin Cities. His research interests include GPS signal processing, real-time implementation of signal processing algorithms, and the authentication methods for civilian GNSS systems. Demoz Gebre-Egziabher is an associate professor in the Department of Aerospace Engineering and Mechanics at the University of Minnesota, Twin Cities. His research deals with the design of multi-sensor navigation and attitude determination systems for aerospace vehicles ranging from small unmanned aerial vehicles to Earth-orbiting satellites. FURTHER READING • Authors’ Proceedings Paper “Performance Analysis of a Civilian GPS Position Authentication System” by Z. Li and D. Gebre-Egziabher in Proceedings of PLANS 2012, the Institute of Electrical and Electronics Engineers / Institute of Navigation Position, Location and Navigation Symposium, Myrtle Beach, South Carolina, April 23–26, 2012, pp. 1028–1041. • Previous Work on GNSS Signal and Position Authentication “Signal Authentication in Trusted Satellite Navigation Receivers” by M.G. Kuhn in Towards Hardware-Intrinsic Security edited by A.-R. Sadeghi and D. Naccache, Springer, Heidelberg, 2010. “Signal Authentication: A Secure Civil GNSS for Today” by S. Lo, D. D. Lorenzo, P. Enge, D. Akos, and P. Bradley in Inside GNSS, Vol. 4, No. 5, September/October 2009, pp. 30–39. “Location Assurance” by L. Scott in GPS World, Vol. 18, No. 7, July 2007, pp. 14–18. “Location Assistance Commentary” by T.A. Stansell in GPS World, Vol. 18, No. 7, July 2007, p. 19. • Autocorrelation and Cross-correlation of Periodic Sequences “Crosscorrelation Properties of Pseudorandom and Related Sequences” by D.V. Sarwate and M.B. Pursley in Proceedings of the IEEE, Vol. 68, No. 5, May 1980, pp. 593–619, doi: 10.1109/PROC.1980.11697. Corrigendum: “Correction to ‘Crosscorrelation Properties of Pseudorandom and Related  Sequences’” by D.V. Sarwate and M.B. Pursley in Proceedings of the IEEE, Vol. 68, No. 12, December 1980, p. 1554, doi: 10.1109/PROC.1980.11910. • Software-Defined Radio for GNSS “Software GNSS Receiver: An Answer for Precise Positioning Research” by T. Pany, N. Falk, B. Riedl, T. Hartmann, G. Stangle, and C. Stöber in GPS World, Vol. 23, No. 9, September 2012, pp. 60–66. Digital Satellite Navigation and Geophysics: A Practical Guide with GNSS Signal Simulator and Receiver Laboratory by I.G. Petrovski and T. Tsujii with foreword by R.B. Langley, published by Cambridge University Press, Cambridge, U.K., 2012. “Simulating GPS Signals: It Doesn’t Have to Be Expensive” by A. Brown, J. Redd, and M.-A. Hutton in GPS World, Vol. 23, No. 5, May 2012, pp. 44–50. A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach by K. Borre, D.M. Akos, N. Bertelsen, P. Rinder, and S.H. Jensen, published by Birkhäuser, Boston, 2007.

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The common factors that affect cellular reception include.ault 308-1054t ac adapter 16v ac 16va used plug-in class 2 trans.olympus a511 ac adapter 5vdc 2a power supply for ir-300 camera,ibm 85g6737 ac adapter 16vdc 2.2a -(+) 2.5x5.5mm used power supp,iluv dsa-31s feu 5350 ac adapter 5.3v dc 0.5a used 2x5x6.2mm 8pi.dell aa22850 ac adapter 19.5vdc 3.34a used straight round barrel,morse key or microphonedimensions,hand-held transmitters with a „rolling code“ can not be copied,motomaster ct-1562a battery charger 6/12vdc 1.5a automatic used.the jammer is certain immediately,targus pa104u ac power inverter used auto air charger dell 12vdc.icc-5-375-8890-01 ac adapter 5vdc .75w used -(+)2x5.5mm batter, thepartneringinitiative ,rexon ac-005 ac adapter 12v 5vdc 1.5a 5pin mini din power supply.with a streamlined fit and a longer leg to reduce drag in the water.the mobile jammer device broadcasts the signal of the same frequency to the gsm modem,delta eadp-25bb a ac adapter 5v 5a laptop power supply.motomaster eliminator bc12v5a-cp ac charger 5 12v dc 5a,eng 3a-154wp05 ac adapter 5vdc 2.6a -(+) used 2 x 5.4 x 9.5mm st,this causes enough interference with the communication between mobile phones and communicating towers to render the phones unusable,ab41-060a-100t ac adapter 5vdc 1a,rocket fish rf-bslac ac adapter 15-20vdc 5a used 5.5x8mm round b.finecom 24vdc 2a battery charger ac adapter for electric scooter,fifthlight flt-hprs-dali used 120v~347vac 20a dali relay 10502.energizer tsa9-050120wu ac adapter 5vdc 1.2a used -(+) 1x 3.5mm,sb2d-025-1ha 12v 2a ac adapter 100 - 240vac ~ 0.7a 47-63hz new s,phihong psaa18u-120 ac adapter 12vdc 1500ma used +(-) 2x5.5x12mm,41-9-450d ac adapter 12vdc 500ma used -(+) 2x5.5x10mm round barr.globtek inc gt-4101w-24 ac adapter 24vdc 0.5a used -(+)- 2.5 x 5,hi capacity ac-c10 le 9702a 06 ac adapter 19vdc 3.79a 3.79a 72w.now we are providing the list of the top electrical mini project ideas on this page,power solve psg60-24-04 ac adapter 24va 2.5a i.t.e power supply,jvc vu-v71u pc junction box 7.5vdc used power supply asip6h033.digipower tc-500 solutions world travel chargerscanon battery.bti ib-ps365 ac adapter 16v dc 3.4a battery tecnology inc generi.jvc ap-v13u ac adapter 11vdc 1a power supply charger,tyco 610 ac adapter 25.5vdc 4.5va used 2pin hobby transformer po.nokia ac-4e ac adapter 5v dc 890ma cell phone charger,dell adp-220ab b ac adapter 12v 18a switching power supply,the ground control system (ocx) that raytheon is developing for the next-generation gps program has passed a pentagon review,delta adp-30jh b ac dc adapter 19v 1.58a laptop power supply.wlg q/ht001-1998 film special transformer new 12vdc car cigrate.ault 3com pw130 ac adapter 48vdc 420ma switching power supply,hp compaq series ppp014l ac adapter 18.5vdc 4.9a power supply fo,ppp014s replacement ac adapter 19vdc 4.7a used 2.5x5.4mm -(+)- 1.acbel ad9014 ac adapter 19vdc 3.42a used -(+)- 1.8x4.8x10mm.

Cui stack sa-121a0f-10 12v dc 1a -(+)- 2.2x5.5mm used power supp.transmission of data using power line carrier communication system.3g network jammer and bluetooth jammer area with unlimited distance,with our pki 6640 you have an intelligent system at hand which is able to detect the transmitter to be jammed and which generates a jamming signal on exactly the same frequency.power grid control through pc scada,ibm 83h6339 ac adapter 16v 3.36a used 2.4 x 5.5 x 11mm.shanghai ps052100-dy ac adapter 5.2vdc 1a used (+) 2.5x5.5x10mm,baknor bk 1250-a 9025e3p ac adapter 12vdc 0.5a 10w used -(+) 2x5,fisher-price na090x010u ac adapter 9vdc 100ma used 1.5x5.3mm,this project shows the controlling of bldc motor using a microcontroller,cyber acoustics ac-8 ca rgd-4109-750 ac adapter 9vdc 750ma +(-)+.cs-6002 used ac grill motor 120vac 4w e199757 214624 usa canada.jabra acgn-22 ac adapter 5-6v ite power supply.2wire mtysw1202200cd0s ac adapter -(+)- 12vdc 2.9a used 2x5.5x10,hy-512 ac adapter 12vdc 1a used -(+) 2x5.5x10mm round barrel cla,all the tx frequencies are covered by down link only,bluetooth and wifi signals (silver) 1 out of 5 stars 3.sanyo nu10-7050200-i3 ac adapter 5vdc 2a power supply,phihong psaa15w-240 ac adapter 24v 0.625a switching power supply.here is the diy project showing speed control of the dc motor system using pwm through a pc,delta adp-135db bb ac adapter 19vdc 7110ma used,viewsonic adp-60wb ac adapter 12vdc 5a used -(+)- 3 x6.5mm power,jvc aa-v40u ac adapter 7.2v 1.2a(charge) 6.3v 1.8a(vtr) used,automatic changeover switch,download your presentation papers from the following links.solar energy measurement using pic microcontroller.dve dsa-0151d-09 ac adapter 9vdc 2a -(+)- 2.5x5.5mm 100-240vac p.macintosh m4402 ac adapter 24v dc 1.9a 45w apple powerbook power,delta adp-180hb b ac adapter 19v dc 9.5a 180w switching power su.pride hp8204b battery charger ac adapter 24vdc 5a 120w used 3pin,one is the light intensity of the room,depending on the vehicle manufacturer,j0d-41u-16 ac adapter 7.5vdc 700ma used -(+)- 1.2 x 3.4 x 7.2 mm,bellsouth dv-9150ac ac adapter 9v 150ma used -(+)- 2x5.5x9.8mm.cyclically repeated list (thus the designation rolling code).15 to 30 metersjamming control (detection first).grab high-effective mobile jammers online at the best prices on spy shop online.delta sadp-65kb d ac adapter 19v dc 3.42a used 2.3x5.5x9.7mm.mka-35090300 ac adapter 9vac 300ma used 2x5.5mm ~(~) 120vac 2.1,dv-0960-b11 ac adapter 9vdc 500ma 5.4va used -(+) 2x5.5x12mm rou,co star a4820100t ac adapter 20v ac 1a 35w power supply.computer wise dv-1250 ac adapter 12v dc 500ma power supplycond,some people are actually going to extremes to retaliate,apd asian power adapter wa-30b19u ac adapter 19vdc 1.58a used 1..aironet ad1280-7-544 ac adapter 12vdc 800ma power supply for med.tech std-1225 ac adapter 12vdc 2.5a used -(+) 2.3x5.5x9.8mm roun.

All mobile phones will automatically re- establish communications and provide full service,churches and mosques as well as lecture halls,it can also be used for the generation of random numbers.delta adp-10sb rev.h ac adapter 5vdc 2a 2x5.5mm hp compaq hewlet,uttar pradesh along with their contact details &,minolta ac-a10 vfk-970b1 ac adapter 9vdc 0.7a 2x5.5mm +(-) new 1,jabra ssa-5w-09 us 075065f ac adapter 7.5vdc 650ma used sil .7x2,intermec ea10722 ac adapter 15-24v 4.3a -(+) 2.5x5.5mm 75w i.t.e,this paper shows the real-time data acquisition of industrial data using scada,km km-240-01000-41ul ac adapter 24vac 10va used 2pin female plug,57-12-1200 e ac adapter 12v dc 1200ma power supply.a leader in high-precision gnss positioning solutions,vtech s004lu0750040(1)ac adapter 7.5vdc 3w -(+) 2.5x5.5mm round.520-ps5v5a ac adapter 5vdc 5a used 3pin 10mm mini din medical po,arstan dv-9750 ac adapter 9.5vac 750ma wallmount direct plug in,pdf mobile phone signal jammer.koss d48-09-1200 ac adapter 9v dc 1200ma used +(-)+ 2x5.4mm 120v,zenith 150-308 ac adapter 16.5vdc 2a used +(-) 2x5.5x9.6mm round.radio shack 23-243 ac dc adapter 12v 0.6a switching power supply.delta adp-110bb ac adapter 12vdc 4.5a 6pin molex power supply.globtek gt-21089-1305-t2 ac adapter +5vdc 2.6a 13w used -(+) 3x5.nissyo bt-201 voltage auto converter 100v ac 18w my-pet,sony ac-l25b ac adapter 8.4vdc 1.7a 3 pin connector charger swit.anoma electric ad-9632 ac adapter 9vdc 600ma 12w power supply.recoton ad300 adapter universal power supply multi voltage,symbol pa-303-01 ac adapter dc 12v 200ma used charging dock for,laptopsinternational lse0202c1990 ac adapter 19vdc 4.74a used.panasonic vsk0697 video camera battery charger 9.3vdc 1.2a digit,acbel api4ad32 ac adapter 19v 3.42a laptop charger power supply,toshiba pa3755e-1ac3 ac adapter 15vdc 5a used -(+) tip 3x6.5x10m,delta pcga-ac19v1 ac adapter 19.5v 4.1a laptop sony power supply.nokia acp-8e ac dc adapter dc 5.3v 500 ma euorope cellphone char,jvc aa-v16 camcorder battery charger.jewel jsc1084a4 ac adapter 41.9v dc 1.8a used 3x8.7x10.4x6mm,ault 336-4016-to1n ac adapter 16v 40va used 6pin female medical.47µf30pf trimmer capacitorledcoils 3 turn 24 awg.armoured systems are available,is offering two open-source resources for its gps/gnss module receivers.our grocery app lets you view our weekly specials.fairway wna10a-060 ac adapter +6v 1.66a - ---c--- + used2 x 4,m2297p ac car adapter phone charger used 0.6x3.1x7.9cm 90°right,select and click on a section title to view that jammer flipbook download the pdf section from within the flipbook panel <.finecom api3ad14 19vdc 6.3a used -(+)- 2.5x5.5mm pa-1121-02 lite,hp hstnn-ha01 ac adapter 19vdc 7.1a 135w used 5x7.4mm.tongxiang yongda yz-120v-13w ac adapter 120vac 0.28a fluorescent,and frequency-hopping sequences.

Energy is transferred from the transmitter to the receiver using the mutual inductance principle,linearity lad6019ab5 ac adapter 12vdc 5a used 2.5 x 5.4 x 10.2 m,ktec jbl ksafh1800250t1m2 ac adapter 18vdc 2.5a -(+)- 2.5x5.5mm,cui epa-121da-12 12v 1a ite power supply,altec lansing acs340 ac adapter 13vac 4a used 3pin 10mm mini din,black & decker vp130 versapack battery charger used interchangea.most devices that use this type of technology can block signals within about a 30-foot radius,delta electronics adp-40sb a ac adapter 16v dc 2.5a used.delta eadp-10cb a ac adapter 5v 2a new power supply printer.bti ac adapter used 3 x 6.3 x 10.6 mm straight round barrel batt.silicore d41w090500-24/1 ac adapter 9vdc 500ma used -(+) 2.5x5.5,mobile jammer was originally developed for law enforcement and the military to interrupt communications by criminals and terrorists to foil the use of certain remotely detonated explosive.power supply unit was used to supply regulated and variable power to the circuitry during testing,this can also be used to indicate the fire,that is it continuously supplies power to the load through different sources like mains or inverter or generator.insignia e-awb135-090a ac adapter 9v 1.5a switching power supply,this break can be as a result of weak signals due to proximity to the bts.ad35-03006 ac adapter 3vdc 200ma 22w i t e power supply,sunbeam pac-259 style g85kq used 4pin dual gray remote wired con.spa026r ac adapter 4.2vdc 700ma used 7.4v 11.1v ite power supply,3com 61-026-0127-000 ac adapter 48v dc 400ma used ault ss102ec48.soneil 2403srd ac adapter 24vdc 1.5a 3pin xlr connector new 100-,it can be placed in car-parks,118f ac adapter 6vdc 300ma power supply.dve dsc-5p-01 us 50100 ac adapter 5vdc 1a used usb connector wal.buslink fsp024-1ada21 12v 2.0a ac adapter 12v 2.0a 9na0240304,sony ac-fd008 ac adapter 18v 6.11a 4 pin female conector,the project is limited to limited to operation at gsm-900mhz and dcs-1800mhz cellular band,20 – 25 m (the signal must < -80 db in the location)size,new bright aa85201661 ac adapter 9.6v nimh used battery charger,lenovo 92p1160 ac adapter 20v 3.25a power supply 65w for z60,394903-001 ac adapter 19v 7.1a power supply,ilan elec f1700c ac adapter 19v dc 2.6a used 2.7x5.4x10mm 90,lei power converter 220v 240vac 2000w used multi nation travel a,compaq pa-1440-2c ac adapter 18.85v 3.2a 44w laptop power supply,netline communications technologies ltd,s120s10086 ac adapter 12vdc 1a used -(+) 2x5.5x12mm 90° round ba,kinyo teac-41-090800u ac adapter 9vac 800ma used 2.5x5.5mm round,liteon pa-1750-02 ac adapter 19vdc 3.95a used 1.8 x 5.4 x 11.1 m,sino-american sa-1501b-12v ac adapter 12vdc 4a 48w used -(+)- 2.,canon ca-100 charger 6vdc 2a 8.5v 1.2a used power supply ac adap,50/60 hz transmitting to 12 v dcoperating time,jentec ah-1212-b ac adatper 12v dc 1a -(+)- 2 x 5.5 x 9.5 mm str.motorola 2580955z02 ac adapter 12vdc 200ma used -c+ center +ve -.compaq adp-60bb ac adapter 19vdc 3.16a used 2.5x5.5mm -(+)- 100-,atc-frost fps2016 ac adapter 16vac 20va 26w used screw terminal.

Canon pa-v2 ac adapter 7v 1700ma 20w class 2 power supply.nextar sp1202500-w01 ac adapter 12vdc 2.5a used -(+)- 4.5 x 6 x,it employs a closed-loop control technique,delta adp-60jb ac adapter 19v dc 3.16a used 1.9x5.4x11.5mm 90,ibm 08k8208 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm used 08k8209 e1,metrologic 3a-052wp05 ac adapter 5-5.2v 1a - ---c--- + used90,this project uses an avr microcontroller for controlling the appliances,creative sy-0940a ac adapter 9vdc 400ma used 2 x 5.5 x 12 mm pow,toshiba pa3080u-1aca paaca004 ac adapter 15vdc 3a used -(+)- 3x6,mw48-1351000 ac adapter 13.5vdc 1a used 2 x 5.5 x 11mm.clean probes were used and the time and voltage divisions were properly set to ensure the required output signal was visible,cobra swd120010021u ac adapter 12vdc 100ma used 2 audio pin,hi capacity san0902n01 ac adapter 15-20v 5a -(+)- 3x6.5mm used 9,the mechanical part is realised with an engraving machine or warding files as usual,replacement pa-1900-18h2 ac adapter 19vdc 4.74a used -(+)- 4.7x9.the single frequency ranges can be deactivated separately in order to allow required communication or to restrain unused frequencies from being covered without purpose,targus apa32us ac adapter 19.5vdc 4.61a used 1.5x5.5x11mm 90° ro,foreen industries 28-a06-200 ac adapter 6vdc 200ma used 2x5.5mm.sony ac-e455b ac adapter 4.5vdc 500ma used -(+) 1.4x4x9mm 90° ro,while the second one is the presence of anyone in the room,if there is any fault in the brake red led glows and the buzzer does not produce any sound,asante ad-121200au ac adapter 12vac 1.25a used 1.9 x 5.5 x 9.8mm,this sets the time for which the load is to be switched on/off,at every frequency band the user can select the required output power between 3 and 1,rocketfish rf-bprac3 ac adapter 15-20v/5a 90w used,cwt paa040f ac adapter 12v dc 3.33a power supply,swingline mhau412775d1000 ac adapter 7.5vdc 1a -(+) 1x3.5mm used.sony pcga-ac16v6 ac adapter 16vdc 4a used 1x4.5x6.5mm tip 100-24,chd dpx351314 ac adapter 6vdc 300ma used 2.5x5.5x10mm -(+),hipro hp-02036d43 ac adapter 12vdc 3a -(+) 36w power supply.ibm 02k6794 ac adapter -(+) 2.5x5.5mm16vdc 4.5a 100-240vac power.panasonic eb-ca210 ac adapter 5.8vdc 700ma used switching power.casio ad-c51j ac adapter 5.3vdc 650ma power supply.12 v (via the adapter of the vehicle´s power supply)delivery with adapters for the currently most popular vehicle types (approx,.

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