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Smaller and Better By Reza Movahedinia, Julien Hautcoeur, Gyles Panther and Ken MacLeod Innovation Insights with Richard Langley THE ANTENNA. This crucial component of any radio transmitting or receiving system has a history that actually predates the invention of radio itself. The first antennas were used by Princeton professor Joseph Henry (after whom the unit of inductance is named) to demonstrate the magnetization of needles by a spark generator. But it was the experiments of Heinrich Hertz in Germany in 1887 that initiated the development of radio transmitters and receivers and the antennas necessary for launching and capturing electromagnetic waves for practical purposes. It was Hertz who pioneered the use of tuned dipole and loop antennas–basic antenna structures we still use today. As communication systems evolved using different parts of the radio spectrum from very low frequencies, through medium-wave frequencies, to high frequencies (shortwave), and to very high frequencies and ultra-high frequencies, and beyond, so did their antennas. There have been significant advances in the design of antennas over the years to improve their bandwidth, beamwidth, efficiency and other parameters. In fact, antenna development, going all the way back to the first antennas, has been one of continuous innovation. GNSS antennas are no different. The antennas for the first civil GPS receivers were bulky affairs. Researchers at the Massachusetts Institute of Technology initially introduced the Macrometer V-1000 in 1982, and Litton Aero Service subsequently commercialized it. It used a crossed-dipole antenna element on a 1-meter square aluminum panel and weighed 18 kilograms. The Jet Propulsion Laboratory’s demonstration GPS receiver, unveiled around the same time, used a small steerable parabolic dish that had to be sequentially pointed at GPS satellites. Both of these antennas gave way to more practical designs. Also introduced in 1982 was the Texas Instruments TI 4100, also known as the Navstar Navigator. This dual-frequency receiver used a conical spiral antenna to provide the wide bandwidth needed to cover both the L1 and L2 frequencies used by GPS. Subsequently, in the mid- to late-1980s, GPS and GLONASS antennas using microstrip patches were introduced for both single- and dual-frequency signal reception. The basic designs introduced then are still with us and are used for single- and multiple-frequency GNSS receivers. Miniature versions are used in some mass-market handheld receivers and for receivers in drone flight control systems. Patch antennas have also been used as elements in survey-grade antennas. A number of other GNSS antenna topologies have been developed including helices and planar spiral designs. Antennas designed for high-precision applications often integrate a ground-plane structure of some kind into the structure such as choke rings. You might think after more than 30 years of GNSS technology development, that there is nothing new to be expected in GNSS antenna development. You would be wrong. In this GPS World 30th anniversary issue Innovation column, we look at the design and performance of an antenna that offers high performance even in challenging environments in a relatively small package. It is appropriate that it is unveiled in this column. After all, Webster’s Dictionary has defined innovation as “the act of innovating or effecting a change in the established order; introduction of something new.” This antenna might very well be a game changer. Global navigation satellite systems (GNSS) have continued to evolve and have become critical infrastructure for all of society. Starting with the awesome engineering feat of the U.S. Global Positioning System and then the more recently developed constellations from other nations, we now have available refined signal structures with ever-improving positioning, navigation and timing accuracy. Expanding use cases has led to the design of GNSS antennas optimized for many different applications. However, new antenna design commonly requires more than simple modifications to existing GPS antenna technologies. Design agility is needed to meet requirements such as wider bandwidth, sculpted radiation patterns (we frequently talk about radiation characteristics even for a receiving antenna assuming antenna reciprocity), optimized/reduced size, better efficiency, lower noise figure, or improvements in the more esoteric parameters such as axial ratio (AR) and phase-center variation (PCV). Nothing changes the widely unappreciated fact that the antenna is the most critical element in precision GNSS systems. In this article, we report on the research and commercial development of a high-performance GNSS antenna by Tallysman, designated “VeroStar.” The VeroStar sets a new performance standard for an antenna of this type and supports reception of the full GNSS spectrum (all constellations and signals) plus L-band correction services. The antenna combines exceptional low-elevation angle satellite tracking with a very high-efficiency radiating element. Precision manufacturing provides a stable phase-center offset (PCO) and low PCV from unit to unit. The performance, compact size and light weight of the VeroStar antenna element make it a good candidate for modern rover and many other mobile GNSS applications. DESIGN OBJECTIVES The design of an improved, high-level GNSS antenna requires consideration of characteristics such as low-elevation angle tracking ability, minimal PCV, antenna efficiency and impedance, axial ratio and up-down ratio (UDR), antenna bandwidth, light weight, and a compact and robust form factor. Low-Elevation Angle Tracking. Today’s professional GNSS users have widely adopted the use of precise point positioning (PPP) including satellite broadcast of the PPP correction data. PPP correction data is broadcast from geostationary satellites, which generally hover at low-elevation angles for many densely populated regions such as Europe and much of North America. The link margin of L-band signals is typically minimal, so that improved gain at these elevation angles is an important attribute. This issue is exacerbated at satellite beam edges and northern latitudes where the link margin is further challenged — a difference of just 1 dB in antenna gain or antenna noise figure can make a big difference in correction availability. A key design parameter in this respect is the antenna G/T, being the ratio, expressed in dB per kelvin, of the antenna element gain divided by the receiver system noise temperature, typically determined by the antenna noise figure. The G/T objective for this antenna was –25.5 dB/K at a 10-degree elevation angle. The gain of most GNSS antenna elements, such as patches and crossed dipoles, rolls off rapidly as the elevation angle decreases toward the horizon. The polarization also becomes linear (rather than circularly polarized) at the lower elevation angles, due to the existence of a ground plane, necessary to increase gain in the hemisphere above the antenna. Improved gain close to the horizon also increases the ability of the receiver to track low-elevation-angle satellites with a concomitant improvement in the dilution of precision parameters (DOPs; a series of metrics related to pseudorange measurement precision). Most of the commercially available GNSS rover antennas have a peak gain at zenith of about 3.5 dBic to 5 dBic with a roll-off at the horizon of 10–12 dB (dBic refers to the antenna gain referenced to a hypothetical isotropic circularly polarized antenna). Typically, this provides an antenna gain at the horizon, at best, of about –5 dBic, which is insufficient for optimized L-band correction usage. In some studies, different antenna types such as helical elements have been proposed to overcome this issue. However, their cylindrical shape and longer length makes them unsuitable for many rover applications. Furthermore, the helix suffers from back lobes that can make the antenna more susceptible to reception of multipath signals from below the upper hemisphere of the antenna. In the VeroStar design, we used wide-bandwidth radiating elements (referred to here as “petals”) that surround a distributed feed network. The petal design is important to achieve superior right-hand circularly polarized (RHCP) gain at low-elevation angles. Tight Phase-Center Variation. The phase center of an ideal antenna is a notional point in space at which all signals are received or transmitted from, independent of the frequency or elevation or azimuth angle of the signal incidence. The phase centers of real-life antennas are less tidy, and the PCV is a measure of the variation of the “zero” phase point as a function of frequency, elevation and azimuth angles. Correction data for phase-center variation is commonly encoded in a standardized antenna exchange format or Antex file, which can be applied concurrently for precision applications. The azimuthal orientation of rover antennas is typically unknown, so that errors for specific orientations of the antenna in the horizontal plane cannot be accounted for. The PCV correction data provided in an Antex file is usually provided as a function of elevation angle and frequency, but with averaged azimuth data for each elevation angle and frequency entry (noazi corrections). Thus, corrections can be applied for each frequency and elevation angle, but errors due to the variation in the azimuthal PCV cannot be corrected in the receiver. For real-time kinematic (RTK) systems, the net system error is the root-mean-square sum of the base and rover antenna PCVs. It is usually possible to accommodate larger base-station antennas, which can commonly provide PCVs approaching +/- 1 mm (such as those from Tallysman VeraPhase or VeraChoke antennas). In this case, the accuracy of the combined system is largely determined by the PCV of the smaller rover GNSS antenna. Thus, even with correction data, azimuthal symmetry in the rover antenna is key. In the VeroStar, this was addressed by obsessive focus on symmetry for both the antenna element structure and the mechanical housing design. Antenna Efficiency and Impedance. Antenna efficiency can be narrowly defined in terms of copper losses of the radiating elements (because copper is not a perfect conductor), but feed network losses also contribute so that the objective must be optimization of both. Physically wide radiating elements are a basic requirement for wider bandwidth, and copper is the best compromise for the radiator metal (silver is better, but expensive and with drawbacks). This is true in our new antenna, which has wide radiating copper petals. However, the petals are parasitic resonators that are tightly coupled to a distributed feed network, which in itself is intrinsically narrowband. The resulting wide bandwidth response results from the load on the feed network provided by the excellent wideband radiation resistance of the petals. This arrangement was chosen because the resulting impedance at the de-embedded antenna feed terminals is close to the ideal impedance needed (50 ohms), thus requiring minimal impedance matching. The near ideal match over a wide bandwidth is very important because it allowed the impedance to be transformed to ideal using a very short transmission line (less than one-quarter of a wavelength), which included an embedded infinite balun (a balun forces unbalanced lines to produce balanced operation). Each of the orthogonal exciter axes are electrically independent and highly isolated electrically (better than –30 dB), even with the parasitic petal coupling. To achieve the desired circular polarization, the two axes are then driven independently in phase quadrature (derived from the hybrid couplers). Thus, the inherently efficient parasitic petals combined with the absolutely minimized losses of the distributed feed network has resulted in a super-efficient antenna structure that will be difficult to improve upon. Axial and Up-Down Ratio. AR characterizes the antenna’s ability to receive circularly polarized signals, and the UDR is the ratio of gain pattern amplitude at a positive elevation angle (α) to the maximum gain pattern amplitude at its mirror image (–α). Good AR and UDR across the full bandwidth of the antenna ensure the purity of the reception of the RHCP GNSS signals and multipath mitigation. GNSS signals reflected from the ground, buildings or metallic structures such as vehicles are delayed and their RHCP purity is degraded with a left-hand circularly polarized (LHCP) component. Because the VeroStar antenna has more gain at low-elevation angles, a very low AR and a high UDR are even more important for mitigating multipath interference. The design objective was an AR of 3 dB or better at the horizon. A Light, Robust and Compact Design. The user community demands ever smaller antennas from antenna manufacturers, but precision rover antennas are typically required to receive signals in both the low (1160 to 1300 MHz) and high (1539 to 1610 MHz) GNSS frequency bands. An inescapable constraint limits the bandwidth of small antennas, so that full-bandwidth (all GNSS signals) rover antennas are unavoidably larger. To date, probably the smallest, high performance all-band antenna was the original Dorne & Margolin C146-XX-X (DM) antenna, which was in its time a tour-de-force. The overall objective for our antenna was to design a small and light-weight radiating element (given the full bandwidth requirement) with a ground-plane size of around 100 millimeters, element height of 30 millimeters or lower, and a weight of 100 grams or less. Ideally, it would be possible to build a smaller version, perhaps with a degree of compromised performance. The applications envisaged for the VeroStar included housed antennas (such as for RTK rovers) and a lightweight element suitable for mobile applications such as drones or even cubesats. ANTECEDENTS The central goal of this project was a precision antenna with a broad beamwidth and a good AR combined with a very tight PCV. The objective was to provide for reception of signals from satellites at low-elevation angles, particularly necessary for reception of L-band correction signals, which can be expected to be incident at elevation angles of 10 degrees to 50 degrees above the horizon. A starting point for this development was an in-depth study of the well-known DM antenna. This antenna has been used for decades in GPS reference stations (usually in choke-ring antennas). It exhibits a higher gain at low-elevation angles (about –3 dBic at the horizon) compared to other antennas on the market (typically –5 dBic or less) and fairly good phase-center stability in a compact design. The antenna structure consists of two orthogonal pairs of short dipoles above a ground plane, with the feeds at the midpoint of the dipoles, as shown in FIGURE 1(a). The antenna can be considered in terms of the ground-plane image, replacing the ground plane with the images of the dipole as shown in FIGURE 1(b). The antenna structure then takes on the form of a large uniform current circular loop similar to the Alford Loop antenna, developed at the beginning of World War II for aircraft navigation. FIGURE 1. (a) Dorne & Margolin (DM) antenna current distribution; (b) Alford Loop antenna. (Image: Tallysman) But the DM antenna does suffer from some drawbacks. By modern standards, the feed network is complex and lossy with costly fabrication, which affects repeatability and reliability. The AR at the zenith is marginal (up to 1.5 dB) and further degrades to 7 dB at the horizon, a factor that becomes less relevant in a choke-ring configuration where the DM element is the most commonly used. However, we took our inspiration from the DM structure and give a nod to its original developers. The structure of the VeroStar antenna is shown in FIGURE 2(a). It consists of bowtie radiators (petals) over a circular ground plane. The petals are coupled to a distributed feed network comprised of a simple low-loss crossed dipole between the petals and the ground plane. The relationship between the petals and the associated feed system provides a current maximum at the curvature of the petals instead of at the center of the antenna as seen in FIGURE 2(b), and in this respect achieves a current distribution similar to that of the DM element. FIGURE 2 . (a) VeroStar antenna element; (b) VeroStar antenna current distribution. (Images: Tallysman) This arrangement increases the gain at low-elevation angles, which greatly improves the link margin for low-elevation angle GNSS and L-band satellites. The circular polarization of the antenna at low-elevation angles can be significantly improved by optimizing the petal’s dimensions such as its height, width and angle with respect to the ground plane. This solves the problem of asymmetry between the electric and magnetic field planes of the antenna radiation pattern, which usually degrades the AR at low-elevation angles. Based on the studies conducted in our project, it was found that the bowtie geometry of the radiators, as well as its coupling to the feeding network, can improve both the impedance and AR bandwidth. By these means, we were able to produce a very wideband, low-loss antenna covering the entire range of GNSS frequencies from 1160 to 1610 MHz. The matching loss associated with the feed network is under 0.3 dB, and the axial ratio remains around 0.5 dB at the zenith and is typically under 3 dB at the horizon over the whole GNSS frequency range. In the early stages of the project, we thought that just four petals would be adequate for our purpose. However, as we progressed with further experimentation and simulation, it became clear that increasing the number of petals substantially improved symmetry, but at the cost of complexity. Ultimately, we determined that eight petals provided considerably better symmetry than four petals with an acceptable compromise with respect to feed complexity. MEASUREMENTS The far-field characteristics of the VeroStar antennas were measured using the Satimo anechoic chamber facilities at Microwave Vision Group (MVG) in Marietta, Georgia, and at Syntronic R&D Canada in Ottawa, Ontario. Data were collected from 1160 to 1610 MHz to cover all the GNSS frequencies. Radiation Patterns and Roll-Off. The measured radiation patterns at different GNSS frequencies are shown in FIGURE 3. The radiation patterns are normalized, showing the RHCP and LHCP gains on 60 azimuth cuts three degrees apart. The LHCP signals are significantly suppressed in the upper hemisphere at all GNSS frequencies. The difference between the RHCP gain and the LHCP gain ranges from 31 dB to 43 dB, which ensures an excellent discrimination between the signals. Furthermore, for other upper hemisphere elevation angles, the LHCP signals stay 22 dB below the maximum RHCP gain and even 28 dB from 1200 to 1580 MHz. Figure 3 also shows that the antenna has a constant amplitude response to signals coming at a specific elevation angle regardless of the azimuth angle. This feature yields an excellent PCV, which will be discussed later. FIGURE 3 . Normalized radiation patterns of the VeroStar antenna on 60 azimuth cuts of the GNSS frequency bands. (Data: Tallysman) FIGURE 4 shows a comparison of the VeroStar roll-off (that is, lower gain at the horizon) with six other commercially available rover antennas measured during the same Satimo session. The VeroStar roll-off is significantly lower than the other rover antennas. The amplitude roll-off from the VeroStar boresight (zenith) to horizon is between 6.5 to 8 dB for all the frequency bands. FIGURE 4. Comparison of the VeroStar roll-off versus six commercially available rover antennas. (Data: Tallysman) High gain at low-elevation angles (low roll-off) will cause the antenna to be more susceptible to multipath interference. Multipath signals are mainly delayed LHCP and RHCP signals. If they arrive at high-elevation angles, there is no issue because the AR of the antenna is low at those angles — thus there will be minimal reception of the multipath signals. However, in conventional antennas, low-elevation-angle multipath degrades observations due to the poor AR performance and low UDR. At lower elevation angles, our antenna has exceptional AR performance and good UDR, which significantly reduces multipath interference. Measurements in a high multipath environment were performed with the antenna and compared to other commercial rover antennas. The measurements show that the phase noise at a 5-degree elevation angle is approximately 6 to 10 millimeters over all GNSS frequencies. The other antennas perform similarly, but have a higher roll-off. This shows that the VeroStar provides a strong signal at low-elevation angles and also has a high level of multipath mitigation performance. Antenna Gain and Efficiency. FIGURE 5 shows the RHCP gain of our antenna at the zenith and at a 10-degree elevation angle for all GNSS frequencies. The measurements show that the antenna exhibits a gain range at the zenith from 4.1 dBic at 1160 MHz to 3.6 dBic at 1610 MHz. The antenna gain at a 10-degree elevation angle varies from –1.45 dBic to –2.2 dBic and is maximum in the frequency range used to broadcast L-band corrections (1539 to 1559 MHz). The radiation efficiency of the antenna is between 70 to 89 percent over the full bandwidth. This corresponds to an inherent (“hidden”) loss of only 0.6 to 1.5 dB, including copper loss, feedline, matching circuit and 90-degree hybrid coupler losses. This performance is a substantial improvement over other antenna elements such as spiral antennas, which exhibit an inherent efficiency loss of close to 4 dB at the lower GNSS frequencies. With the integration of wideband pre-filtering as well as a low-noise amplifier (LNA), we measured a G/T of –25 dB/K at a 10-degree elevation angle. FIGURE 5. RCHP gain at zenith and 10-degree elevation angle. (Data: Tallysman) Axial Ratio. The AR values of the VeroStar antenna at different elevation angles are shown in FIGURE 6. The antenna has exceptional AR performance over all GNSS frequency bands and at all elevation angles, with the value no greater than 3.5 dB. This increases the antenna’s ability to reject LHCP signals caused by reflections from nearby cars or buildings. Therefore, the susceptibility of the antenna to multipath interference is greatly reduced. FIGURE 6 Axial ratio versus frequency of the VeroStar at different elevation angles. (Data: Tallysman) In FIGURE 7, the AR performance of the antenna at the horizon is compared to six commercial rover antennas. The VeroStar antenna has an average AR of 2 dB at the horizon (competitive antennas are typically around 6 dB), showing its ability to track pure RHCP signals and enabling outstanding low-elevation-angle multipath mitigation. FIGURE 7. Comparison of the VeroStar axial ratio at the horizon versus six commercially available rover antennas. (Data: Tallysman) Phase-Center Variation. We developed Matlab code to estimate the PCV from the measured radiation pattern. FIGURE 8 shows the maximum PCV of the VeroStar antenna and six commercial rover antennas for four common GNSS frequencies. It can be seen that the antenna has a maximum total PCV of less than 2.9 millimeters for all frequency bands, which is less than the other commercially available rover antennas tested. Furthermore, the PCV of the antenna does not vary significantly with frequency. This comparison confirms the exceptional low PCV of our antenna. FIGURE 8. Comparison of the VeroStar maximum PCV at the horizon versus six commercially available rover antennas. (Data: Tallysman) LOW-NOISE AMPLIFIER DESIGN The best achievable carrier-to-noise-density ratio (C/N0) for signals with marginal power flux density is limited by the efficiency of each of the antenna elements, the gain and the overall receiver noise figure. This can be quantified by the G/T parameter, which is usually dominated by the noise figure of the input LNA. In the LNA design for our antenna, the received signal is split into the lower GNSS frequencies (from 1160 to 1300 MHz) and the higher GNSS frequencies (from 1539 to 1610 MHz) in a diplexer connected directly to the antenna terminals and then pre-filtered in each band. This is where the high gain and high efficiency of the antenna element provides a starting advantage, since the unavoidable losses introduced by the diplexer and filters are offset by the higher antenna gain, and this preserves the all-important G/T ratio. That being said, GNSS receivers must accommodate a crowded RF spectrum, and there are a number of high-level, potentially interfering signals that can saturate and desensitize GNSS receivers. These signals include, for example, mobile-phone signals, particularly Long-Term Evolution (LTE) signals in the 700-MHz band, which are a hazard because of the potential for harmonic generation in the GNSS LNA. Other potentially interfering signals include Globalstar (1610 to 1618.25 MHz), Iridium (1616 to 1626 MHz) and Inmarsat (1626 to 1660.5 MHz), which are high-power communication satellite uplink signals close in frequency to GLONASS signals. The VeroStar LNA design is a compromise between ultimate sensitivity and ultimate interference rejection. A first defensive measure in the LNA is the addition of multi-element bandpass filters at the antenna element terminals (ahead of the LNA). These have a typical insertion loss of 1 dB because of their tight passband and steep rejection characteristics. However, the LNA noise figure is increased approximately by the additional filter-insertion loss. The second defensive measure in the design is the use of an LNA with high linearity. This is achieved without any significant increase in LNA power consumption, using LNA chips that employ negative feedback to provide well-controlled impedance and gain over a very wide bandwidth. Bear in mind that while an antenna installation might initially be determined to have no interference, subsequent introduction of new telecommunication services may change this, so interference defense is prudent even in a quiet radio-frequency environment. A potentially undesirable side effect of tight pre-filters is the possible dispersion that can result from variable group delay across the filter passband. Thus, it is important to include these criteria in the selection of suitable pre-filters. The filters in our LNA give rise to a maximum variation of less than 10 nanoseconds in group delay over both the lower GNSS frequencies (from 1160 to 1300 MHz) and the higher GNSS frequencies (from 1539 to 1610 MHz). CONCLUSION In this article, we have described the performance of a novel RHCP antenna optimized for modern multi-constellation and multi-frequency GNSS rover applications. We have developed a commercially viable GNSS antenna with superior electrical properties. The VeroStar antenna has high sensitivity at low elevation angles, high efficiency, very low axial ratio and high phase-center stability. The lightweight and compact antenna element is packaged in several robust housings designed and built for durability to stand the test of time, even in harsh environments. The VeroStar antenna has sufficient bandwidth to receive all existing and currently planned GNSS signals, while providing high performance standards. Testing of the antenna has shown that the novel design (curved petals coupled to crossed driven dipoles associated with a high performance LNA) has excellent performance, especially with respect to axial ratios, cross polarization discrimination and phase-center variation. These features make the VeroStar an ideal rover antenna where low-elevation angle tracking is required, providing users with new levels of positional precision and accuracy. ACKNOWLEDGMENTS Tallysman Wireless would like to acknowledge the partial support received from the European Space Agency and the Canadian Space Agency. REZA MOVAHEDINIA is a research engineer with Tallysman Wireless, Ottawa, Ontario, Canada. He has a Ph.D. degree in electrical and computer engineering from Concordia University, Montreal, Quebec, Canada. JULIEN HAUTCOEUR is the director of GNSS product R&D at Tallysman Wireless. He received a Ph.D. degree in signal processing and telecommunications from the Institute of Electronics and Telecommunications of Université de Rennes 1, Rennes, France. GYLES PANTHER is president and CTO of Tallysman Wireless. He holds an honors degree in applied physics from City University, London, U.K. KEN MACLEOD is a product-line manager with Tallysman Wireless. He received a Bachelor of Science degree from the University of Toronto. FURTHER READING GNSS Antennas in General “Antennas” by M. Maqsood, S. Gao and O. Montenbruck, Chapter 17 in Springer Handbook of Global Navigation Satellite Systems edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017. GPS/GNSS Antennas by B. Rama Rao, W. Kunysz, R. Fante and K. McDonald, published by Artech House, Boston and London, 2013. “GNSS Antennas: An Introduction to Bandwidth, Gain Pattern, Polarization, and All That” by G.J.K. Moernaut and D. Orban in GPS World, Vol. 20, No. 2, Feb. 2009, pp. 42–48. “A Primer on GPS Antennas” by R.B. Langley in GPS World, Vol. 9, No. 7, July 1998, pp. 50–54. Tallysman VeraPhase GNSS Antenna Static Testing and Analysis of the Tallysman VeraPhase VP6000 GNSS Antenna by R.M. White and R.B. Langley, a report prepared for Tallysman Wireless Inc., Feb. 2018. “Evolutionary and Revolutionary: The Development and Performance of the VeraPhase GNSS Antenna” by J. Hautcoeur, R.H. Johnston and G. Panther in GPS World, Vol. 27, No. 7, July 2016, pp. 42–48. The Alford Loop “Ultrahigh-frequency Loop Antennas” by A. Alford and A.G. Kandoian in Electrical Engineering, Vol. 59, No. 12, Dec. 1940, pp. 843–848. doi: 10.1109/EE.1940.6435249.

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Fsp fsp050-1ad101c ac adapter 12vdc 4.16a used 2.3x5.5mm round b,philips 4222 029 00030 ac adapter 4.4vdc 0.85va used shaver powe,uttar pradesh along with their contact details &,canon d6420 ac adapter 6.3v dc 240ma used 2 x 5.5 x 12mm,by the time you hear the warning,rocketfish nsa6eu-050100 ac adapter 5vdc 1a used.2110 to 2170 mhztotal output power,linearity lad6019ab5 ac adapter 12vdc 5a used 2.5 x 5.4 x 10.2 m,arduino are used for communication between the pc and the motor.li shin 0226a19150 ac adapter 19vdc 7.89a -(+) 2.5x5.5mm 100-240.toshiba adpv16 ac dc adapter 12v 3a power supply for dvd player,solex tri-pit 1640c ac adapter 16.5vac 40va 50w used screw termi,communication system technology use a technique known as frequency division duple xing (fdd) to serve users with a frequency pair that carries information at the uplink and downlink without interference.nikon mh-23 ac adapter 8.4vdc 0.9a 100-240vac battery charger po,with a maximum radius of 40 meters,baknor 66dt-12-2000e ac dc adapter 12v 2a european power supply.ibm 35g4796 thinkpad ac dc adapter 20v dc 700 series laptop pow,liteon pa-1650-02 ac adapter 19vdc 3.42a 65w used -(+) 2.5x5.5mm,nothing more than a key blank and a set of warding files were necessary to copy a car key.hp photosmart r-series dock fclsd-0401 ac adapter used 3.3vdc 25.dell adp-150eb b ac adapter 19.5v dc 7700ma power supply for ins.code-a-phonedv-9500-1 ac adapter 10v 500ma power supply,520-ntps12 medical power source12vdc 2a used 3pin male adapter p,the if section comprises a noise circuit which extracts noise from the environment by the use of microphone,ibm 08k8212 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm used power supp,with a single frequency switch button,jvc ap-v16u ac adapter 11vdc 1a power supply,tyco 610 ac adapter 25.5vdc 4.5va used 2pin hobby transformer po.digipower acd-fj3 ac dc adapter switching power supply.cord connected teac-57-241200ut ac adapter 24vac 1.2a ~(~) 2x5.5.compaq 2812 series ac adapter 18.5v 2.5a 35w presario laptop pow,sony ericsson cst-75 4.9v dc 700ma cell phone charger,the circuit shown here gives an early warning if the brake of the vehicle fails.this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs,it was realised to completely control this unit via radio transmission,the transponder key is read out by our system and subsequently it can be copied onto a key blank as often as you like.creative ud-1540 ac adapter dc 15v 4a ite power supplyconditio,motorola bb6510 ac adapter mini-usb connector power supply car c,this system also records the message if the user wants to leave any message.dell pa-3 ac adapter 19vdc 2.4a 2.5x5.5mm -(+) power supply.casio ad-1us ac adapter 7.5vdc 600ma used +(-) 2x5.5x9.4mm round,am-12200 ac adapter 12vdc 200ma direct plug in transformer unit,altec lansing s024eu1300180 ac adapter 13vdc 1800ma -(+) 2x5.5mm.automatic telephone answering machine,pega nintendo wii blue light charge station 300ma,condor dsa-0151d-12 ac adapter 12v dc 1.5a2pins mo power suppl,such vehicles and trailers must be parked inside the garage.energizer pc-1wat ac adapter 5v dc 2.1a usb charger wallmount po,uniden ac6248 ac adapter 9v dc 350ma 6w linear regulated power s.toshiba ap13ad03 ac adapter 19v dc 3.42a used -(+) 2.5x5.5mm rou,lectroline 41a-d15-300(ptc) ac adapter 15vdc 300ma used -(+) rf,ibm 85g6737 ac adapter 16vdc 2.2a -(+) 2.5x5.5mm used power supp.dynex dx-nb1ta1 international travel adapter new open pack porta.chd scp0501500p ac adapter 5vdc 1500ma used -(+) 2x5.5x10mm roun.a cellphone jammer is pretty simple,traders with mobile phone jammer prices for buying,delta sadp-65kb d ac adapter 19v dc 3.42a used 2.3x5.5x9.7mm.business listings of mobile phone jammer,is offering two open-source resources for its gps/gnss module receivers.lambda dt60pw201 ac adapter 5vdc 6a 12v 2a lcd power supply 6pin,canon cb-5l battery charger 18.4vdc 1.2a ds8101 for camecorder c,atc-520 dc adapter used 1x3.5 travel charger 14v 600ma.ibm 11j8627 ac adapter 19vdc 2.4a laptop power supply.

Dve dsa-0051-05 fus 55050 ac adapter 5.5vdc .5a usb power supply,jammer free bluetooth device upon activation of the mobile jammer,i can say that this circuit blocks the signals but cannot completely jam them,netbit dsc-51fl 52100 ac adapter 5v 1a switching power supply,aiphone ps-1820 ac adapter 18v 2.0a video intercom power supply,jvc aa-v11u camcorder battery charger.a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals,which is used to test the insulation of electronic devices such as transformers,dell da90ps0-00 ac adapter 19.5vdc 4.62a used 1 x 5 x 7.4 x 12.5.soneil 2403srd ac adapter +24vdc 1.5a 36w 3pin 11mm redel max us,cell phone jammer is an electronic device that blocks transmission of …,ac/dc adapter 5v 1a dc 5-4.28a used 1.7 x 4 x 12.6 mm 90 degree.samsung atadd030jbe ac adapter 4.75v 0.55a used,3 x 230/380v 50 hzmaximum consumption.sceptre ad2405g ac adapter 5vdc 3.8a used 2.2 x 5.6 x 12.1 mm -(.hewlett packard series ppp009h 18.5v dc 3.5a 65w -(+)- 1.8x4.7mm,cwt pag0342 ac adapter 5vdc 12v 2a used 5pins power supply 100-2,black & decker s036c 5102293-10 ac adapter 5.5vac 130ma used 2.5,ad-1235-cs ac adapter 12vdc 350ma power supply,kingshen mobile network jammer 16 bands highp power 38w adjustable desktop jammer ₹29.artin dc 0750700 ac adapter 7.5vdc 700ma used power supply.ancon 411503oo3ct ac adapter 15vdc 300ma used -(+) rf antenna co,delta adp-5fh c ac adapter 5.15v 1a power supply euorope.the inputs given to this are the power source and load torque.epson a391uc ac adapter 13.5vdc 1.5a used -(+) 3.3x5mm 90° right,sony ac-l25a ac adapter 8.4vdc 1.7a 3 pin connector charger ac-l.aok ak02g-1200100u ac adapter 12vdc 1a used 2 x 5.5 x 10mm,gn netcom ellipe 2.4 base and remote missing stand and cover.dv-2412a ac adapter 24vac 1.2a ~(~) 2x5.5mm 120vac used power su.two way communication jammer free devices,similar to our other devices out of our range of cellular phone jammers.lenovo adp-65kh b ac adapter 20vdc 3.25a -(+)- 2.5x5.5x12.5mm,phihong psm11r-120 ac adapter 12vdc 1.6a -(+) 2.1.x5.5mm 120vac,motorola psm4963b ac adapter 5vdc 800ma cellphone charger power,texas instruments xbox 5.1 surround sound system only no any thi.it is also buried under severe distortion,jammers also prevent cell phones from sending outgoing information,2110cla ac adapter used car charger.this circuit shows the overload protection of the transformer which simply cuts the load through a relay if an overload condition occurs,this paper describes the simulation model of a three-phase induction motor using matlab simulink,eleker ac car adapter phone charger 4-10vdc used 11-26v,anta mw57-1801650a ac adapter 18v 1.65a power supply class 2,toshiba pa3201u-1aca ac adapter 15v 5a used -(+) 3.1x6.5mm lapto,as many engineering students are searching for the best electrical projects from the 2nd year and 3rd year,here a single phase pwm inverter is proposed using 8051 microcontrollers,asante ad-121200au ac adapter 12vac 1.25a used 1.9 x 5.5 x 9.8mm,cellphone jammer complete notes,nokia ac-4x ac adapter 5vdc 890ma used 1 x 2 x 6.5mm.compaq pa-1530-02cv ac adapter 18.5vdc 2.7a used 1.7x5mm round b,the program will be monitored to ensure it stays on,a mobile device to help immobilize.motorola psm4250a ac adapter 4.4vdc 1.5a used cellphone charger,find here mobile phone jammer.black&decker ps 160 ac adapter 14.5vdc 200ma used battery charge,tdp ep-119/ktc-339 ac adapter 12vac 0.93amp used 2.5x5.5x9mm rou,ast ad-5019 ac adapter 19v 2.63a used 90 degree right angle pin.aopen a10p1-05mp ac adapter 22v 745ma i.t.e power supply for gps,motorola fmp5202c ac adapter 5v 850ma cell phone power supply,lien chang lca01f ac adapter 12vdc 4.16a spslcd monitor power.kodak vp-09500084-000 ac adapter 36vdc 1.67a used -(+) 6x4.1mm r.hp pa-2111-01h ac dc adapter 19v 2950ma power supply,solytech ad1712c ac adapter 12vdc 1.25a 2x5.5mm used 100-240vac,chicony a10-018n3a ac adapter 36vdc 0.5a used 4.3 x 6 x 15.2 mm.

Kodak k4500 ni-mh rapid battery charger2.4vdc 1.2a wall plug-i,replacement 1650-05d ac adapter 19.5v 3.34a used -(+)- 5x7.4mm r,nintendo ds dsi car adapter 12vdc 4.6vdc 900ma used charger bric,65w-dlj104 ac adapter 19.5v dc 3.34a dell laptop power supply,hon-kwang hk-a112-a06 ac adapter 6vdc 0-2.4a used -(+) 2.5x5.5x8,delta eadp-60kb ac adapter 12vdc 5a -(+) 2.5x5.5mm used 100-240v.ibm pscv540101a ac adapter 12v 4.5v used 4.4 x 5.8 x 10.3mm roun,replacement m8482 ac adapter 24vdc 2.65a used g4 apple power.90 % of all systems available on the market to perform this on your own,jabra ssa-5w-05 us 0500018f ac adapter 5vdc 180ma used -(+) usb,d4530 ac adapter dc 4.5v 300ma plug in class 2 transformer power.baknor bk 3500-b3345pip ac adapter 3vdc 500ma used 1x2.2x9.7mm,placed in front of the jammer for better exposure to noise,in-li yl-12-12 ac adapter 12vac 12va used ~(~) 2pin din female p.tec b-211-chg-qq ac adapter 8.4vdc 1.8a battery charger,phihong psm25r-560 ac adapter 56vdc 0.45a used rj45 ethernet swi.changzhou linkie lk-dc-210040 ac adapter 21vdc 400ma used 2.1 x,cui inc epa-201d-12 ac adapter 12vdc 1.66a used 8 pin mini din c.dee ven ent dsa-0301-05 5v 3a 3pin power supply.li shin emachines 0225c1965 ac adapter 19vdc 3.42a notebookpow,delta adp-90sb bb ac adapter 19vdc 4.74a -(+) 2.5x5.5mm used 100,polaroid k-a70502000u ac adapter 5vdc 2000ma used (+) 1x3.5x9mm,and lets you review your prescription history,71109-r ac adapter 24v dc 350ma power supply tv converter used,sony dcc-e345 ac adapter 4.5v/6v 1.5v/3v 1000ma used -(+)-.audiovox cnr505 ac adapter 7vdc 700ma used 1 x 2.4 x 9.5mm,acbel api3ad25 ac adapter 19vdc 7.9a used -(+) 2x5.5mm 100-240va.here is a list of top electrical mini-projects,duracell cef-20 nimh class 2 battery charger used 1.4vdc 280ma 1.it consists of an rf transmitter and receiver,by activating the pki 6100 jammer any incoming calls will be blocked and calls in progress will be cut off,gamestop 5v wii remote conteroller charging dock,ktec ksa0100500200d5 ac adapter 5vdc 2a used -(+) 1x3.4mm strai,minolta ac-9 ac-9a ac adapter 4.2vdc 1.5a -(+) 1.5x4mm 100-240va.seidio bcsi5-bk usb ac multi function adapter usb 5vdc 1a used b.someone help me before i break my screen,embassies or military establishments.a portable mobile phone jammer fits in your pocket and is handheld,ibm adp-40bb ac adapter 20-10vdc 2-3.38a power supply.replacement pa-10 ac adapter 19.5v 4.62a used 5 x 7.4 x 12.3mm,liteon pa-1750-02 ac adapter 19vdc 3.95a used 1.8 x 5.4 x 11.1 m,panasonic eb-ca340 ac adapter 5.6vdc 400ma used phone connector,cobra ga-cl/ga-cs ac adapter 12vdc 100ma -(+) 2x5.5mm power supp,bionx hp1202l3 01-3443 ac adaptor 45.65vdc 2a 3pin 10mm power di,sunbeam bc-1009-ul battery charger 1.4vdc 150ma used ni-mh aa/aa,ilan elec f1700c ac adapter 19v dc 2.6a used 2.7x5.4x10mm 90,such as propaganda broadcasts,cincon trg70a240 ac adapter 24vdc 3a used 2.5x5.5mm -(+)- round,ibm ac adapter-30 84g2128 4pin 20-10vdc 1.5-3a power supply.gateway2000 adp-45cb ac dc adapter 19v 2.4a power supply,apd da-2af12 ac adapter used -(+)2x5.5mm 12vdc 2a switching powe.d9-12-02 ac adapter 6vdc 1.2a -(+) 1200ma used 2x5.5mm 120vac pl.ibm 12j1445 ac adapter 16vdc 2.2a power supply 4pin 350 700 755.altec lansing s012bu0500250 ac adapter 5vdc 2500ma -(+) 2x5.5mm.fsp 150-aaan1 ac adapter 24vdc 6.25a 4pin 10mm +(::)- power supp,preventively placed or rapidly mounted in the operational area,when the mobile jammer is turned off.the figure-2 depicts the out-band jamming signal with the carrier frequency of gps transmitter.ikea kmv-040-030-na ac adapter 4vdc 0.75a 3w used 2 pin din plug.dve dvr-0920ac-3508 ac adapter 9vac 200ma used 1.1x3.8x5.9mm rou,coming data cp1230 ac adapter 12vdc 3a used -(+) 2x5.5mm round b.nikon mh-63 battery charger 4.2vdc 0.55a used for en-el10 lithiu.globtek gt-21089-1509-t3 ac adapter 9vdc 1a used -(+) 2.5x5.5mm.

For technical specification of each of the devices the pki 6140 and pki 6200,cx huali 66-1028-u4-d ac adapter 110v 150w power supply,l.t.e gfp121u-0913 ac adapter 9vdc 1.3a -(+) used 2x5.5mm,replacement 324816-001 ac adapter 18.5v 4.9a used,makita dc9100 fast battery chrgar 9.6vdc 1.5a used drill machine.4312a ac adapter 3.1vdc 300ma used -(+) 0.5x0.7x4.6mm round barr.pure energy cs4 charging station used 3.5vdc 1.5a alkaline class.nokia ac-10u ac adapter 5vdc 1200ma used micro usb cell phone ch,we would shield the used means of communication from the jamming range,all mobile phones will indicate no network incoming calls are blocked as if the mobile phone were off,the zener diode avalanche serves the noise requirement when jammer is used in an extremely silet environment,thermo gastech 49-2163 ac adapter 12.6vdc 220/70ma battery charg,conair 0326-4108-11 ac adapter 1.2v 2a power supply,creative a9700 ac adapter9vdc 700ma used -(+)- 2x5.5mm 120vac.a jammer working on man-made (extrinsic) noise was constructed to interfere with mobile phone in place where mobile phone usage is disliked,anti jammer bluetooth wireless earpiece unlimited range,ault t48-161250-a020c ac adapter 16va 1250ma used 4pin connector.toshiba adp-60fb 19vdc 3.42a gateway laptop power supply,rayovac rayltac8 ac adapter battery charger 15-24vdc 5a 90w max.dv-1215a-1 ac adapter 9v 1.5a 30w ae-980 power supplycondition,darelectro da-1 ac adapter 9.6vdc 200ma used +(-) 2x5.5x10mm rou.d-link jta0302b ac adapter 5vdc 2.5a used -(+) 90° 120vac power,yhsafc0502000w1us ac adapter 5vdc 2a used -(+) 1.5x4x9mm round b.compaq ppp002d ac adapter 18.5v dc 3.8a used 1.8x4.8x9.6mm strai,conair 0326-4102-11 ac adapter 1.2vdc 2a 2pin power supply.sharp ea-28a ac adapter 6vdc 300ma used 2x5.5x10mm round barrel.chi ch-1234 ac adapter 12v dc 3.33a used -(+)- 2.5x5.5mm 100-240.mw mw48-9100 ac dc adapter 9vdc 1000ma used 3 pin molex power su.dve dsa-0131f-12 us 12 ac adapter 12vdc 1a 2.1mm center positive..

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