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An Answer for Precise Positioning Research By Thomas Pany, Nico Falk, Bernhard Riedl, Tobias Hartmann, Günter Stangl, and Carsten Stöber INNOVATION INSIGHTS by Richard Langley WHAT IS THE IDEAL GNSS RECEIVER? Well, that depends on what you mean by “ideal.” If we take it to mean the simplest, conceptually, yet the most capable and adaptable receiver, then we would just connect an analog-to-digital converter (ADC) to an antenna and pass the converter’s output to a digital signal processor whose software would transform the received signal into the desired result with the utmost speed and precision. There are certain technological limitations that currently preclude fully developing such a device but we are getting very close to the ideal and practical implementations already exist. Such a GNSS receiver is an example of a software-defined radio — a radio-communications architecture in which as much of the operation of a receiver (or a transmitter) as feasible is performed by software in an embedded system or on a personal computer (PC). Now, we can’t simply connect an ADC to an antenna since the strength of GNSS signals falls well below the sensitivity threshold of real ADCs and those that can directly digitize microwave radio frequencies are rather power hungry. Therefore, the front end of a real software GNSS receiver includes a low-noise preamplifier, filters, and one or more downconverters to produce an analog intermediate-frequency signal that passes to a high-speed ADC. The digitized signal is provided at the output of the front end in a convenient format, which, for processing signals on a PC, is typically USB 2.0 with its maximum signaling rate of 480 megabits per second. All baseband signal processing is then carried out in the programmable microprocessor. Software GNSS receivers offer a number of advantages over their hardware cousins. Foremost is their flexibility, which permits easy and rapid changes to accommodate new radio frequency bands, signal modulation types and bandwidths, and baseband algorithms. This flexibility is beneficial not only for multi-GNSS operation but also for prototyping algorithms for conventional hardware designs. Another advantage is their use in embedded systems such as smartphones and wireless personal digital assistants. Software GNSS receivers are also a boon for teaching, where a student can tweak a particular operating parameter and immediately see the effect. And given their remarkable flexibility, software GNSS receivers can be adapted to a variety of special scientific and engineering research applications such as reflectometry and signal analysis. In this month’s “Innovation,” we look into the development and capabilities of one modern software GNSS receiver in an effort to answer the question “What is the ideal GNSS receiver for precise positioning research?” “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. Personal-computer-based software receivers have found broad use as R&D tools for testing new signal processing algorithms, for analyzing received GNSS signals, and for integrating various sensors with GNSS. Software receivers also provide a consistent framework for GNSS signal samples, correlator values, pseudoranges, positions, assistance data, and sensor (inertial) data, and often act as integration platforms for prototype navigation systems. The distinctive feature of PC-based software receivers is their ability to work in post-processing mode in addition to real-time operation and the support of high-performance central processing units (CPUs). So far, software receivers are typically not used as operational receivers — neither in the mass market, nor in the professional sector, nor as a reference station where a PC would already be available. The last point can be explained by the fact that most software receivers can only process a limited number of frequency bands (sometimes just L1) and are often limited to small bandwidth signals (such as that of the L1 C/A-code signal or the L2 civil signal (L2C)). Improvements of the PC-based software receiver SX-NSR achieved at the end of 2010 and in early 2011 try to overcome these limitations. They include the first real-time implementation of P-code processing on L2, a unique method for processing the ultra-wide Galileo AltBOC signals on E5, and a method to synchronize two NavPort-4 frontends (each supporting four frequency bands of 15 MHz bandwidth) via a hardware link. The SX-NSR, which has been developed in cooperation with the Universität der Bundeswehr München in Munich, Germany, runs under the Windows operating system (XP or 7) and supports processing of GNSS signals plus sensor data (such as that from an inertial measurement unit, or IMU) in real time and in post-processing mode. It supports all the civil GPS, GLONASS, Galileo, and Compass signals. User-defined signals can be included by providing the pseudorandom noise (PRN) codes and the associated tracking parameters. The computational real-time performance can be characterized by two rules-of-thumb for acquisition and tracking. Acquisition is based on a flexible coherent and noncoherent integration and may be accelerated by a graphics card based on the Compute Unified Device Architecture (CUDA) — a parallel-computing architecture developed by Nvidia for graphics processing but also useful for accelerating non-graphics applications. Depending on the graphics card type, a few million or many millions of equivalent correlators are available to detect even the weakest signals quickly. Stable tracking is done with multiple correlators. An x86 CPU core supports around 20 channels (for a laptop) to 30 channels (for a PC) at an average CPU load below 50–60 percent. With that CPU load, the software has enough reserve (in terms of the size of the sample buffer) to cope with latencies introduced by the non-real-time Windows operating system. In post-processing, a virtually unlimited number of channels or correlators is available. The SX-NSR software typically connects to the NavPort-4 front end via a single USB 2.0 connector. One front end supports four RF paths with 15-MHz bandwidth in the L-band. One band is sampled at 40.96 MHz with 12-bit precision. Small batches of samples are transferred with 12 bits at regular intervals to the PC for increased spectral analysis possibilities but the continuous transfer is usually done with just 2 bits. Decimation by a factor of two (yielding a sample rate of 20.48 MHz) and/or bit reduction are options to limit the data transfer bandwidth on the USB bus. The NavPort also includes configurable notch and finite-impulse-response (FIR) filters working with 12-bit precision and 40.96-MHz data rate. The SX-NSR further supports standard output formats (such as Receiver Independent Exchange (RINEX) format or that of the Radio Technical Commission for Maritime Services (RTCM)), has a graphical user interface, and a freely user-accessible application programming interface (API) in the C programming language. A reference station was established with the SX-NSR for the International GNSS Service (IGS) Multi-GNSS Experiment (M-GEX) starting on February 1, 2012, at the Observatory Graz in Austria (marker name GRAB). The data is routinely processed by the European Reference Frame analysis center at Observatory Lustbuehel, Graz, Austria, with Bernese Software 5.0, and shows results with a quality that is virtually no different than that of commercial hardware receivers. All-in-view tracking of the four GNSS constellations on all frequencies (see TABLE 1) has been achieved with an off-the-shelf $1,000 PC, two synchronized NavPorts, and the SX-NSR software. In particular, the front end receives Compass B1, B2, and B3 signals and currently the software is tracking two of the geostationary Earth orbit (GEO) satellites, a few of the inclined geosynchronous orbit (IGSO) satellites, and the medium Earth orbit (MEO) satellites at Graz on B1 and B2. There are plans to implement tracking of the B3 signal for the M1 satellite and that of satellite-based augmentation system (SBAS) satellites on L5. Table 1. Frequency bands supported by the dual NavPort-4 receiver. Typical received carrier-to-noise-density-ratio (C/N0) values recorded at station GRAB are shown in FIGURE 1. Freely accessible GRAB data in RINEX format can be downloaded from several data archive sites (see Further Reading online). The SX-NSR software receiver provides a GNSS development and research framework with the API opening it up for user-implemented algorithms. The user may implement only small portions of new code (such as a special acquisition technique) and for the rest of the receiver rely on the well-known behavior of the SX-NSR’s framework. A number of applications are possible using the flexibility of a software receiver; some of them are described in this article. Figure 1. C/N0 values for five typical satellites, one each for GPS, GLONASS, Galileo, Compass, and the European Geostationary Navigation Overlay Service (EGNOS) SBAS as recorded at Observatory Graz. The Front End The front-end frequency plan was adjusted to have a clean spectrum free of internal interference. This is of utmost importance as software receivers are often used to detect and mitigate interference especially for the Galileo E5 and E6 frequency bands due to overlapping radio navigation services. An inter-front-end link enables synchronization of two NavPort-4 devices. It generates a synchronous reference clock for a proper phase relationship. Moreover, a trigger is used to adjust the digital data stream of both devices. One possible application of the inter-front-end link technology is to easily double the number of available GNSS frequencies. Another possible application is the building of a dual-antenna solution. For this purpose, each NavPort-4 device handles the same GNSS frequencies, but from different antennas. Whereas within each NavPort, a quad analog-to-digital converter (ADC) synchronously samples the four received GNSS signals, the synchronicity between two NavPorts is more complex. For the inter-front-end link, both devices have to use the same 10-MHz clock reference for a synchronous setup. This is reached by using the reference clock output of the master device as reference clock input of the slave device as depicted in FIGURE 2. It is also possible to connect both NavPort-4 devices to a single external clock reference. Each device generates its own 40.96-MHz sample rate from this reference. The phase difference of the 40.96-MHz sample rate is measured in the master and slave with a phase detector. The first input of the detector is the local 40.96-MHz clock. The second input is the 40.96-MHz clock from the other NavPort-4 with a different phase alignment due to ambiguities in its generation and cable delay. The phase detector measures the phase difference between both clocks. The low-pass-filtered output of this measurement is digitized with an ADC. If this measurement is within a phase range of ±7 degrees at 40.96 MHz, which corresponds to ±14 centimeters, the coarse synchronization is finished. If the value is not within this range, the synchronization algorithm repeats. After starting the data processing for both devices simultaneously with an implemented digital trigger, the phase difference between master and slave clock could be measured continuously for later fine-tuning in the SX-NSR to achieve an accuracy of much below 1 degree at 40.96 MHz, which corresponds to ±2 centimeters. The synchronization algorithm is verified by connecting two L1-capable NavPorts to the same antenna. The phase and code delay can then be determined from receiver single-differences of GPS L1 C/A-code-derived phase and code measurements. Actually, this delay estimation is part of an attitude solution (see below) and an example is shown in FIGURE 3. The code delay here is around 50 centimeters and includes the RF filter delay difference of around 40 centimeters (which can be calibrated and is stable over power cycles) in addition to the synchronization delay (here around 10 centimeters). The phase delay is naturally determined modulo one cycle and shows warm-up effects of 1.4 centimeters during the first few minutes of operation. Figure 3. Inter-front-end hardware delay variation on a GPS L1 signal. GNSS Reference Station Although the GPS modernization process is ongoing and more and more L2C-capable satellites are in orbit, tracking of the encrypted P-code signal on L2 is still a key element for any receiver to be considered as a reference station or geodetic receiver. Dual-frequency observations need to be available for the full GPS constellation. A possible option to retrieve full wavelength carrier-phase observations and code ranges on L2 is cross-correlation tracking of the encrypted P-code signal. The receiver computes the cross-correlation function between the raw L1 and L2 samples over a long coherent interval as shown in FIGURE 4. The encrypted P-code stream, identical on L1 and L2, is represented by c(tµ). Figure 4. Cross-correlation block diagram. A receiver internal complex carrier is generated (see frequency compensation in Figure 4), whose frequency equals the Doppler shift frequency plus the intermediate-frequency difference between L1 and L2. This frequency is generally different for each satellite. The L1 signal is delayed to compute the cross-correlation function for several code-phase taps. The cross-correlation function is computed using the predicted Doppler difference based on the Doppler frequency estimated from L1 with complex-valued baseband samples. A number of batches are collected and a post-correlation fast Fourier transform is applied. The parameter values shown in TABLE 2 result in a total coherent integration time of 6.4 seconds. Table 2. SX-NSR cross-correlation parameter values. The result is the cross-correlation function as a function of code phase and Doppler. Using interpolation techniques, the position of the peak is determined, which then gives the delay and Doppler shift of the L2 signal with respect to the L1 signal. The complex argument of the peak value gives the L2-L1 carrier-phase differences. Those differences are filtered and are then added to the L1 parameters to give the L2P code estimates. We use two first-order Kalman filters (one for the code, one for the phase) to smooth the cross-correlation estimates. The code filter is updated with the estimated delay and the Doppler; the phase filter is updated with the estimated Doppler and phase. Cycle slips are detected if the L1-L2 phase changes are too high. Loss-of-lock is detected by comparing the estimated L2 C/N0 value against a threshold. After several Kalman filter tuning steps, the L2P signal is tracked down to low elevation angles. For example, the GPS Block IIF satellite PRN1 was tracked over a whole pass without cycle slips as shown in the code-minus-carrier plot in FIGURE 5.  Figure 5. Code minus carrier-phase measurements for GPS PRN1 at site GRAB on day of year 106, 2012. One of the key applications of a professional GNSS receiver is its use as a GNSS reference station. Using a software receiver for this purpose would also provide increased monitoring capabilities to detect (un)intentional inference via RF spectral analysis or to detect signal anomalies due to satellite failures or multipath. Furthermore, it is useful for a number of scientific experiments and research topics such as scintillation monitoring or atmospheric occultation studies. Other GNSS Signals The inclusion of new GNSS signals in a software receiver is typically straightforward. The PRN codes need to be loaded and the tracking parameters (such as carrier frequency, integration time, error correction scheme, phase relation of signal components data/pilot, correlator positions, and discriminator type) can be selected without source code modification. If a hand-over from a different signal is performed (such as from GPS L1 to GPS L5) and if the first signal has already been synchronized to the transmit time by decoding the time-of-week, then it is possible to directly resolve the code ambiguity of the new signal. If this is not possible, a navigation message decoder has to be implemented to retrieve the time-of-week, which mostly has to be in the source code. Galileo AltBOC. An important exception to this rule is the Galileo AltBOC signal due to its high bandwidth. A conventional view on the AltBOC signal processing would require a sample rate of at least two times the total signal bandwidth. Depending on how many outer AltBOC side lobes are considered, this results in a sampling rate of 102 megasamples per second or more. This is undesirable for a cost-efficient software receiver solution, regarding the data transfer and the CPU load. The AltBOC processing inside the SX-NSR relies on the fact that both frequency bands E5a and E5b are sampled coherently and this coherency can be exploited to reconstruct the full AltBOC signal. The accuracy of the AltBOC navigation signal is concentrated in the main BOC sidelobes itself. More specifically, the thermal noise and multipath performance are dependent on the Gabor bandwidth, which represents the curvature of the correlation function at the tracking point. Thus a similar Gabor bandwidth can be obtained by sampling the E5a and the E5b band separately. This is the key idea of the resulting AltBOC processing scheme. The E5a and E5b signal samples are generated synchronously inside the same ADC chip and are transferred via the USB bus to the PC running the SX-NSR. The SX-NSR first acquires and tracks the signal separately on E5a and E5b. As it is quite efficient to run the E5a and E5b tracking on separate threads (and on separate CPU cores), the combination of E5a and E5b correlation values to E5 correlation values is done at the post-correlation level. There is no feedback from the E5 channel to the E5a/b channels. The channel maintains its own numerically controlled oscillator (NCO). A dedicated transformation is used to account for NCO differences between the E5a/b NCO values and the E5 NCO values. It is basically a sinc-interpolation in the code-phase direction and accounts for Doppler and carrier-phase differences. The transformed correlation values are added and yield an approximation to the AltBOC correlation function. The E5 correlation values are used to compute the discriminator values to update the E5 tracking loops. The E5 NCO values are used to compute the code pseudoranges and carrier-phase measurements, the Doppler frequency, and the C/N0 values, which are the primary outputs of the E5 receiver. Although the E5 receiver is a somehow a virtual receiver (that is, without correlators), it has the same user interface including most of the configuration parameters, output (for example, multi-correlator), and API. With AltBOC tracking, the Galileo satellites deliver code and phase measurements on five different carrier frequencies. A code-minus-carrier plot is shown in FIGURE 6. The code accuracy of the AltBOC signal is striking. The E6 signal is severely impacted by the present interference, and phase tracking is only possible for higher elevation angles. Figure 6. Code minus carrier-phase measurements for Galileo PRN12 at site GRAB on day of year 104, 2012. Polyfit and Vector Tracking A software receiver should provide a transparent way to retrieve pseudorange measurements that is well understood and can be well modeled. It should also provide a flexible input to control tracking NCO values. Both points are important if the receiver is part of larger navigation system (such as an integrated GNSS/INS system). Conventional delay-lock loop (DLL) / frequency-lock loop (FLL) / phase-lock loop (PLL) configuration is one option and is well understood by all GNSS researchers and engineers. It has, however, two major drawbacks. The loops introduce time correlations that cannot be easily modeled in a positioning Kalman filter, especially if low bandwidths (carrier aiding) are used. Second, the internal parameters of a DLL are difficult to match to a deeply coupled GPS/INS system. One way to overcome this is a method called polyfit tracking based on a rather old Jet Propulsion Laboratory patent (U.S. Patent No. 4821294). The idea behind this is to decouple pseudorange determination from the NCO counters. This is accomplished by forming the pseudoranges at the integrate-and-dump rate (such as 50 Hz) and to add the discriminator values to them. The resulting pseudorange is then obtained via a polyfit over the measurement interval. The time correlation of the measurements is solely determined by the discriminator values, and they compensate for the NCO correlations. A nice example is the application of this method to vector tracking. In vector tracking the NCO values are determined via a line-of-sight projection of the last position, velocity, and time (PVT) estimate and this estimate is usually slightly delayed. Furthermore, the line-of-sight projection is not perfect due to inevitable modeling errors (such as atmospheric delay errors). Thus the NCO does not follow the received signal as well as for DLL/FLL/PLL tracking. This is not a problem as the difference is captured in the discriminator values. FIGURE 7 shows the output of the method for a measurement interval of 0.5 second, one GPS C/A-code signal and for a dynamic user. The PVT update happens with a delay of about 100 milliseconds, changing the Doppler frequency. This resulting phase slope discontinuity is nicely compensated by the phase discriminator. The actual measurements are marked as brown stars in Figure 7. The method can also be applied to slave a channel to a master channel. This is useful for reflectometry, for example, where the master channel locks onto a line-of-sight signal and the slave channel tracks the reflected signal from sea surface. Figure 7. NCO-based phases (green) plus discriminator values (yellow) and polyfit for carrier-phase, code, and Doppler tracking (dynamic user, GPS C/A-code tracking). With multiple correlators (for example, nine correlators equally spaced from -0.5 to 0.3 chip for GPS C/A-code tracking), the polyfit method can be extended in a natural way to estimate and mitigate multipath. Using the polyfit carrier estimate, the multi-correlator values are coherently combined over the measurement interval and then a correlation function model is fitted to it. An eventually presented data bit is estimated and wiped off. The correlator fit starts with the assumption that only the line-of-sight signal is present. If the chi-squared value is above a certain threshold, the correlator fit is repeated assuming additionally one multipath signal. Up to two multipath signals can be estimated. The performance of this method can be tested with an RF signal generator. The scenario includes the line-of-sight signal (GPS C/A-code) and one multipath signal. The initial multipath delay is 0 meters and increases slowly (5.7 millimeters per second). The standard tracking method uses a multipath-mitigating double-delta code discriminator formed from four correlators (-0.2, -0.1, 0.1, 0.2) and an arctan carrier discriminator. Standard tracking is used to control the NCO values. FIGURE 8 shows that multipath is detected for delays larger than 15 meters. The detection performance depends on the carrier-phase difference of the line-of-sight and multipath signal, but for delays larger than 32 meters, multipath is always detected. If multipath is detected, the corrected ranges and C/N0 values are significantly improved. Figure 8. SX-NSR real-time carrier-phase multipath detection and mitigation performance for a GPS C/A-code signal with a -10 dB multipath signal (standard tracking shown in black, multipath-estimating discriminator output shown in red). The polyfit method is used routinely in the reference station and has also been tested in a dynamic scenario. A bus drive near the IFEN office in Poing, Germany, with the antenna mounted on the roof has been carried out. Even in this rural area, short-term shading and multipath severely distort single channel (DLL/PLL) tracking causing rather large position errors (red dots in FIGURE 9). With a simple switch in the software, the NCO control can be switched from DLL/PLL to vector tracking (polyfit tracking is always on with the same fit parameters). If the standard point positioning (SPP) solution is used to control the NCO values (yellow dots), the errors are already drastically reduced because the NCOs follow the position and not the reflected signals. Also, erratic NCO jitter preceding loss-of-lock events is now eliminated. A further improvement is achieved if the PVT solution is computed by a Kalman filter (green dots), giving finally the typical high-navigation accuracy of modern GNSS receivers even with partial signal blocking. Dual-Antenna Heading Determination The bus drive mentioned above has actually been carried out with two antennas on the roof top with the aim of demonstrating the dual-antenna performance of the software receiver to determine heading. Two synchronized NavPorts have been used, both receiving GPS C/A-code signals (more frequencies would even be more beneficial and possible, but such a test has not yet been carried out). The software is fully prepared to handle data streams from two antennas and one option is to use the same NCO for both antennas. That is, the master antenna data is used to realize vector tracking and the discriminators of the slave channels capture the relative movement of the slave antenna to the master antenna. Again, polyfit tracking provides a natural framework to cope with this data. Attitude is determined with receiver single-difference observations. It is beneficial to form this difference as early as possible in the receiver processing, that is, immediately after correlation. Thus carrier-phase tracking is based on receiver single-difference correlators, being the product of the complex-conjugate master prompt correlator and the slave prompt correlator (both obviously for the same GNSS signal). The heading is shown in FIGURE 10. As reference, a GPS/INS system was used that calibrated the IMU during the first 300 seconds. One sees that the polyfit plus difference correlator is able to track the carrier phase continuously over 400 seconds in the rural test drive, although there is high multipath and some shading even for the high-elevation-angle satellites. Switching off only one option (vector tracking or the difference correlator) introduces cycle slips and corrupts the heading solution. Figure 10. Heading and heading error for the dual-antenna test.  Conclusions Currently, we see two main applications for software receivers. First, they may replace hardware receivers if the increased software receiver performance/flexibility justifies the increased power consumption and size. Several features have been shown in this article, and the possibility to do post-processing and the high-power CPU for customized algorithms are striking arguments for software receivers. On the other hand, software receivers may be customized by inserting user-specific code via the API offering enormous possibilities. Acknowledgments The research leading to the AltBOC results and the difference correlator results has received funding from the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement numbers 248151 and 247866, respectively. This article is based, in part, on the award-winning paper “Wide-band Signal Processing Features for Reference Station use of a PC-based Software Receiver: Cross-correlation Tracking on GPS L2P, AltBOC and the Inter-frontend Link for up to Eight Frequency Bands” presented at ION GNSS 2011, the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation, held in Portland, Oregon, September 19–23, 2011. Manufacturers The IFEN GmbH NavPort/SX-NSR receiver at station GRAB is fed by a Leica Geosystems AG LEIAR25.R4 antenna with a LEIT radome. The kinematic test used a NovAtel Inc. SPAN GNSS/inertial system. THOMAS PANY works for IFEN GmbH in Poing, Germany, as a senior research engineer in the GNSS receiver department. He also works as a lecturer (Priv.-Doz.) at the Universität der Bundeswehr München (UniBwM) in Munich, Germany. NICO FALK works for IFEN GmbH in the receiver technology department. BERNHARD RIEDL works for IFEN GmbH as product manager for SX-NSR. TOBIAS HARTMANN works for IFEN GmbH in the receiver technology department. GÜNTER STANGL is an officer of the Austrian Federal Office for Metrology and Surveying and works half time at the Space Research Institute of the Austrian Academy of Sciences. CARSTEN STÖBER is a research associate at UniBwM.   FURTHER READING • Authors’ Proceedings Paper “Wide-band Signal Processing Features for Reference Station Use of a PC-based Software Receiver: Cross-correlation Tracking on GPS L2P, AltBOC and the Inter-frontend Link for up to Eight Frequency Bands” by T. Pany, N. Falk, B. Riedl, T. Hartmann, J. Winkel, and G. Stangl in Proceedings of ION GNSS 2011, the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, September 19–23, 2011, pp. 753–766. • IFEN Software Receiver Website • Overviews of Software GNSS Receivers “Real-Time Software Receivers: Challenges, Status, Perspectives” by M. Baracchi-Frei, G. Waelchli, C. Botteron, and P.-A. Farine in GPS World, Vol. 20, No. 9, September 2009, pp. 40–47. “GNSS Software Defined Radio: Real Receiver or Just a Tool for Experts?” by J.-H. Won, T. Pany, and G. Hein in Inside GNSS, Vol. 1, No. 5, July–August 2006, pp. 48–56 “Satellite Navigation Evolution: The Software GNSS Receiver” by G. MacCougan, P.L. Normark, and C. Ståhlberg in GPS World, Vol. 16, No. 1, January 2005, pp. 48–55. • Software GNSS Receiver Algorithms and Implementations 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. Navigation Signal Processing for GNSS Software Receivers by T. Pany, published by Artech House, Norwood, Massachusetts, 2010. 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. “GNSS Radio: A System Analysis and Algorithm Development Research Tool for PCs” by J.K. Ray, S.M. Deshpande, R.A. Nayak, and M.E. Cannon in GPS World, Vol. 17, No. 5, May 2006, pp. 51–56. Fundamentals of Global Positioning System Receivers: A Software Approach, 2nd Edition, by J. B.-Y. Tsui, published by John Wiley & Sons, Inc., Hoboken, New Jersey, 2005. • Galileo Signal Tracking “Performance Evaluation of Single Antenna Interference Suppression Techniques on Galileo Signals using Real-time GNSS Software Receiver” by A.S. Ayaz, R. Bauernfeind, J. Jang, I. Kraemer, D. Dötterbock, B. Ott, T. Pany, and B. Eissfeller in Proceedings of ION GNSS 2010, the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, September 21–24, 2010, pp. 3330–3338. • Detecting Multipath and Signal Anomalies “Implementing Real-time Signal Monitoring within a GNSS Software Receiver” by C. Stöber, F. Kneißl, I. Krämer, T. Pany, and G. Hein in Proceedings of ENC-GNSS 2008, Toulouse, April 23–25, 2008. • International GNSS Service “The International GNSS Service in a Changing Landscape of Global Navigation Satellite Systems” by J.M. Dow, R.E. Neilan, and C. Rizos in Journal of Geodesy special issue, “The International GNSS Service (IGS) in a Changing Landscape of Global Navigation Satellite Systems,” Vol. 83, Nos. 3-4, 2009, pp. 191–198, doi: 10.1007/s00190-008-0300-3. “The International GNSS Service: Any Questions?” by A.W. Moore in GPS World, Vol. 18, No. 1, January 2007, pp. 58–64. IGS Multi-GNSS Experiment (M-GEX) website: http://www.igs.org/mgex. Software receiver data archive for site GRAB: ftp://olggps.oeaw.ac.at/pub/igsmgex/.        

signal jammer 100m

The pocket design looks like a mobile power bank for blocking some remote bomb signals,dve dsa-0251-05 ac adapter 5vdc 5a used 2.5x5.5x9mm 90 degree.redline tr 48 12v dc 2.2a power supply out 2000v 15ma for quest_.samsung atadm10cbc ac adapter 5v 0.7a usb travel charger cell ph.vipesse a0165622 12-24vdc 800ma used battery charger super long.car charger 2x5.5x10.8mm round barrel ac adapter.kensington system saver 62182 ac adapter 15a 125v used transiet.phihong psm11r-120 ac adapter 12vdc 1.6a -(+) 2.1.x5.5mm 120vac,1800 to 1950 mhz on dcs/phs bands,1920 to 1980 mhzsensitivity,here is the circuit showing a smoke detector alarm,specificationstx frequency.eng epa-201d-07 ac adapter 7vdc 2.85a used -(+) 2x5.5x10mm round.nokia acp-9u ac adapter 6.2v 720ma new 1.2 x 3.4 x 7.7mm round.replacement 324816-001 ac adapter 18.5v 4.9a used,htc psaio5r-050q ac adapter 5v dc 1a switching usb power supply.the complete system is integrated in a standard briefcase,this page contains mobile jammer seminar and ppt with pdf report,patients with diabetic foot ulcer (dfu) have a high risk of limb amputation as well as higher five-year mortality rates than those for several types of cancer,power solve up03021120 ac adapter 12vdc 2.5a used 3 pin mini din,milwaukee 48-59-2401 12vdc lithium ion battery charger used,cyber acoustics d41-09-600 ac adapter 9vdc600ma 3h33 e144991,btc adp-305 a1 ac adapter 5vdc 6a power supply.extra shipping charges for international buyers partial s&h paym,baknor bk 1250-a 9025e3p ac adapter 12vdc 0.5a 10w used -(+) 2x5.eng 3a-161da12 ac adapter 12vdc 1.26a used 2x5.5mm -(+)- 100-240,fone gear 01023 ac adapter 5vdc 400ma used 1.1 x 2.5 x 9mm strai,depending on the vehicle manufacturer,black and decker etpca-180021u2 ac adapter 26vdc 210ma class 2,bionx hp1202l3 01-3444 ac adaptor 37vdc 2a 4pin xlr male used 10.finecom ad-6019v replacement ac adapter 19vdc 3.15a 60w samsung,lg pa-1900-08 ac adapter 19vdc 4.74a 90w used -(+) 1.5x4.7mm bul,for any further cooperation you are kindly invited to let us know your demand.qun xing ac adapter 1000ma used 100vac 2pin molex power supply,startech usb2sataide usb 2.0 to sata ide adapter,dell la90pe1-01 ac adapter 19.5vdc 4.62a used -(+) 5x7.4mm 100-2.cet technology 48a-18-1000 ac adapter 18vac 1000ma used transfor.by the time you hear the warning.pace fa-0512000su ac adapter 5.1vdc 2a used -(+) 1.5x4x9mm round.toshiba pa3378e-2aca ac adapter 15vdc 5a used -(+)- 3x6.5mm,cyber acoustics md-75350 ac adapter 7.5vdc 350ma power supply.cincon tr100a240 ac adapter 24vdc 4.17a 90degree round barrel 2.,mobile jammers block mobile phone use by sending out radio waves along the same frequencies that mobile phone use,black & decker fs18c 5103069-12 ac adapter 21.75v dc 210ma used,dve dsc-5p-01 us 50100 ac adapter 5vdc 1a used usb connector wal,load shedding is the process in which electric utilities reduce the load when the demand for electricity exceeds the limit,brother epa-5 ac adapter 7.5vdc 1a used +(-) 2x5.5x9.7mm round b,nokia no5100 6100 car power adapter 1x3.5mm round barrel new cha,nec adp52 ac adapter 19vdc 2.4a 3pin new 100-240vac genuine pow.this device is the perfect solution for large areas like big government buildings,ibm aa20530 ac adapter 16vdc 3.36a used 2.5 x 5.5 x 11mm.hi capacity ea1050a-190 ac adapter 19vdc 3.16a used 5 x 6 x 11,ault t57-182200-j010g ac adapter 18v ac 2200ma used.bellsouth u090050a ac adapter 9vac 500ma power supply class 2.

Sony ac-fd008 ac adapter 18v 6.11a 4 pin female conector.tpt jsp033100uu ac adapter 3.3vdc 1a 3.3w used 3x5.5mm round bar,hk-b518-a24 ac adapter 12vdc 1a -(+)- ite power supply 0-1.0a,accordingly the lights are switched on and off,sceptre ad2405g ac adapter 5vdc 3.8a used 2.2 x 5.6 x 12.1 mm -(,hallo ch-02v ac adapter dc 12v 400ma class 2 power supply batter,hipro hp-o2040d43 ac adapter 12vdc 3.33a used -(+) 2.5x5.5mm 90,it is efficient in blocking the transmission of signals from the phone networks,which is used to provide tdma frame oriented synchronization data to a ms,duracell dr130ac/dc-b ac adapter 0-24v dc 0.6a 0.7a 130w used po,fujitsu nu40-2160250-i3 ac adapter 16vdc 2.5a used -(+)- 1 x 4.6.casio ad-1us ac adapter 7.5vdc 600ma used +(-) 2x5.5x9.4mm round,high power hpa-602425u1 ac adapter 24vdc 2.2a power supply,lei mt20-21120-a01f ac adapter 12vdc 750ma new 2.1x5.5mm -(+)-,15.2326 ac adapter 12vdc 1000ma -(+) used 2.4 x 5.5 x 8.3.5mm,buslink fsp024-1ada21 12v 2.0a ac adapter 12v 2.0a 9na0240304.while the second one shows 0-28v variable voltage and 6-8a current.upon activation of the mobile jammer,dell fa90pe1-00 ac adapter 19.5vdc 4.62a used -(+) 5x7.3x12.5mm.lighton pb-1200-1m01 ac adapter 5v 4a switching ac power supply,sceptre ad1805b 5vdc 3.7a used 3pin mini din ite power supply.finecom ac dc adapter 15v 5a 6.3mmpower supply toshiba tec m3,you may write your comments and new project ideas also by visiting our contact us page,when communication through the gsm channel is lost.liteon pa-1900-24 ac adapter 19v 4.74a acer gateway laptop power.when vt600 anti- jamming car gps tracker detects gsm jammer time continue more than our present time,samsung atads30jbs ac adapter 4.75vdc 0.55a used cell phone trav,dell ad-4214n ac adapter 14vdc 3a power supply,hp ppp017l ac adapter 18.5vdc 6.5a 5x7.4mm 120w pa-1121-12h 3166.dv-0960-b11 ac adapter 9vdc 500ma 5.4va used -(+) 2x5.5x12mm rou.ingenico pswu90-2000 ac adapter 9vdc 2a -(+) 2.5x5.5 socket jack,and eco-friendly printing to make the most durable,sony ericsson cst-18 ac adapter 5vdc 350ma cellphone charger,sony vgp-ac19v57 19.5v dc 2a used -(+)- 4.5x6mm 90° right angle.the cockcroft walton multiplier can provide high dc voltage from low input dc voltage,we hope this list of electrical mini project ideas is more helpful for many engineering students.ad35-04505 ac dc adapter 4.5v 300ma i.t.e power supply.hp pa-1181-08 series hstnn-la03 ac adapter 180w 19.5v 9.2a ite.li shin lse9802a1240 ac adapter 12vdc 3.33a 40w round barrel.battery mc-0732 ac adapter 7.5v dc 3.2a -(+) 2x5.5mm 90° 100-240,dve dsa-6pfa-05 fus 070070 ac adapter +7vdc 0.7a used.hp pa-1650-32hj ac adapter 19.5vdc 3.5a used 5 x 7.4 x 12.6 mm s.panasonic kx-tca1 ac adapter 9vdc 350ma +(-) 2x5.5mm used cordle,110 to 240 vac / 5 amppower consumption.finecom api3ad14 19vdc 6.3a used -(+)- 2.5x5.5mm pa-1121-02 lite.ap 2700 ac dc adapter 5.2v 320ma power supply.compaq pp007 ac adapter 18.5vdc 2.7a used -(+)- 1.7x4.8mm auto c.dell scp0501000p ac adapter 5vdc 1a 1000ma mini usb charger,atlinks 5-2418a ac adapter 9vac 400ma ~(~) 2x5.5mm 90° used 120v,motorola spn4474a ac adapter 7vdc 300ma cell phone power supply,compaq 239427-003 replacement ac adapter 18.5vdc 3.5a 65w power.astrodyne spu16a-105 ac adapter 12vdc 1.25a -(+)- 2x5.5mm switch,ad-4 ac adapter 6vdc 400ma used +(-) 2x5.5mm round barrel power.2100 to 2200 mhz on 3g bandoutput power.

Dve dsa-0101f-05 up ac adapter 5v 2a power supply.madcatz 2752 ac adapter 12vdc 340ma used -(+) class 2 power supp,chd ud4120060060g ac adapter 6vdc 600ma 14w power supply,ibm 85g6733 ac adapter 16vdc 2.2a 4 pin power supply laptop 704.brushless dc motor speed control using microcontroller,dve dsa-0601s-121 1250 ac adapter 12vdc 4.2a used 2.2 x 5.4 x 10,samsung pscv420102a ac adapter 14vdc 3a power supply.ault 5305-712-413a09 ac adapter 12v 5vdc 0.13a 0.5a power supply.access to the original key is only needed for a short moment.an optional analogue fm spread spectrum radio link is available on request,meadow lake tornado or high winds or whatever,thus any destruction in the broadcast control channel will render the mobile station communication,after years of campaigning for the dissolution of the long-gun registry,ge nu-90-5120700-i2 ac adapter 12v dc 7a used -(+) 2x5.5mm 100-2.eng 3a-122du12 ac adapter 12vdc 1a -(+) 2x5.5mm used power suppl.delta adp-30ar a ac adapter 12vdc 2.5a used 2x5.5x9mm 90°round b.black & decker s036c 5102293-10 ac adapter 5.5vac 130ma used 2.5,cui inc epas-101w-05 ac adapter 5vdc 2a (+)- 0.5x2.3mm 100-240va.all these security features rendered a car key so secure that a replacement could only be obtained from the vehicle manufacturer,qualcomm taaca0101 ac adapter 8.4vdc 400ma used power supply cha.be possible to jam the aboveground gsm network in a big city in a limited way,nec adp-50mb ac adapter 19v 2.64a laptop power supply.sony ac-l200 ac adapter 8.4vdc 1.7a camcorder power supply.lenovo 42t4434 ac adapter 20vdc 4.5a new -(+) 5.1x8x11.3mm,apple powerbook m1893 ac adapter 16vdc 1.5a 16v 1a used 4 pin di,.

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