All photos courtesy of the author.
Where Is It?
By Paul Alves, Carmen Wong, Matthew Clampitt, Eric Davis and Eunju Kwak
INNOVATION INSIGHTS with Richard Langley
WE LIVE IN A POLLUTED WORLD. Sometimes even pristine environments are desecrated.
No, I’m not talking here about the rubbish on Mount Everest, nor the leaching of heavy metals from tailing ponds, nor the plastic trash in the oceans, nor the sulfur dioxide in the atmosphere.
I’m talking about radio-frequency pollution. Just as we would like to have our physical environment free of pollution for our better health and that of the ecosystem, we would like the radio spectrum to be free of pollution so that its users — virtually everyone on the planet — can have a better RF experience, whether it be when listening to the radio, using a cell phone or operating a GNSS receiver. We usually call RF pollution interference, or RFI for short, as it interferes with the signal we are trying to receive.
RFI can be accidental or deliberate, in which case we call it jamming. As a shortwave radio enthusiast, I am familiar with both types of RFI. Although the majority of the world’s radio stations attempt to coordinate their broadcasts to ensure that two stations don’t try to beam their signals to a particular area on the same or an adjacent frequency at the same time, it does happen, ruining reception. And if a country doesn’t want its citizens listening to certain foreign radio broadcasts, it might attempt to jam them as the Soviet Union did in the past and as China, North Korea, Cuba and several other countries still do.
In this month’s column, we look at GNSS interference. In many cases, GNSS interference is accidental, with a nearby radio device putting out a signal at a fundamental frequency or a harmonic, which lies within the passband of one of the GNSS frequencies.
It could be intentional, too, and we’ve all heard about GPS jammers including the so-called personal privacy devices that deliberately interfere with GPS signal reception. Is there any way to detect GNSS interference and to find its source so that remedial action can be taken? Yes and yes. A team of authors from NovAtel tell us how.
Interference is a growing concern among GNSS users, particularly in parts of the world where radio frequency transmission is not strictly regulated. Intentional interference and jamming is cheap and relatively easy to obtain in the form of personal privacy devices (PPDs). These devices can sometimes cause unintended interference and jamming to important infrastructure such as an airport. In this article, we describe a method for creating an interference map using the NovAtel OEM7 Interference Tool Kit (ITK). The ITK is capable of detecting and eliminating interference, and can be used to measure the power of a received interferer. When data is collected for an area around a static and continuously operating interference source, it can be used to map out the interference over the affected area. We overview a method for mapping the interference and, using a model of power loss over distance, creating a map of the interferer’s likely position. We also discuss simulated results and three case studies with live (real-data) interference sources from India, Canada and Japan.
NovAtel introduced the ITK in 2016. The ITK’s interference detection provides a list of sources, which includes an estimate of the frequency, bandwidth and power of the measured interference. It also provides the power levels across the entire frequency band of the front end. Either of these can be used as measurements of the received interference power levels. When the power levels for a given frequency are combined from multiple locations, they can be used to estimate the power and location of the interference source. The received power levels can also be combined to estimate the interference power as a function of location. The performance degradation experienced by one receiver at a given interference level can be extrapolated to other receivers at the estimated interference levels.
INTERFERENCE DETECTION
The ITK tools include the ability to visualize the power received across the input frequencies (front-end) bands. This can be used to quickly and easily identify any irregularities in the spectrum. These irregularities could be caused by internal interference, which is interference between electrical components introduced through hardware integration or installation. It can also be caused by external interference, such as by a PPD or other nearby radio transmitter.
The ITK’s detection feature identifies potential interference and provides a list of the interference power, frequency and bandwidth. This makes it easier for integrators to automate responses to potential interference without the need to scan the spectrum themselves. FIGURE 1 shows the received signal power and interference detection threshold for the GPS L1 frequency band. In this case there is no interference detected.
FIGURE 1. Received signal power (blue) and interference detection threshold (red) for L1.
The detection threshold is adjustable. However, if it is set too high, it can cause interference to be undetected; if it is set too low, it can cause false detection. For this example, a fairly low value was chosen because we were willing to manually identify the interference source and ignore any false detection.
The ITK also includes tools to mitigate interference, limiting or eliminating its impact. This includes a high dynamic range mode, which is effective in reducing the impact of interference. If this is not sufficient, then notch or low-pass filters also can be applied to completely cut out parts of the spectrum to neutralize the impact of interference or jamming.
FREE-SPACE LOSS
The mapping algorithm, which will be discussed later, requires a model of the power loss as a function of distance (d) to the transmitter. As the wave spreads from the transmission source, the power is lost according to:
(1)
where Lp (dB) is the power loss in dB, d is the distance in meters, and λ is the wavelength in meters. This equation can be expanded into a function of frequency (f, in Hz) and distance (d, in millimeters). Changing the units in this equation changes the constants.
(2)
For example, if the transmitter is broadcasting at 1.237 GHz, then Equation (2) gives
(3)
This ideal power loss is significantly increased by physical obstructions that are common, such as vehicles, buildings, trees or the terrain type. Different materials can have significantly different impacts on the power loss.
Some researchers have used a precomputed power map and map matching for indoor positioning. This method uses the expected received power to position a receiver. The same algorithm that is used to position the receiver could also be used to position the transmitter.
FIGURE 2 shows the received power as a function of distance that was observed for the Calgary test. There is a large variability in the power, likely due to natural obstructions.
FIGURE 2. Received power as a function of distance from the transmitter.
The equation for the line of best fit of this data is significantly different from Equation (3). This is likely due to the obstructions and limited number of data points. Due to problems with inaccuracies with this data fit, any further power calculations will use Equation (2).
MAPPING THE INTERFERENCE IMPACT
Using a single observation of the received interference power, a profile of the transmit power as a function of location can be created using a power decay curve similar to that shown in Figure 2. If we assume that the transmitter is at a given position and use the decay curve through the observed power, then we can estimate the transmit power at that location. When we do this for multiple locations, a power profile is created. This process is shown in FIGURE 3. When these plotted estimates are connected continuously, then we get a power profile.
FIGURE 3. Received power as a function of distance from the transmitter.
This power profile could pertain to a lower power transmitter that is relatively close to the receiving antenna or could be a stronger transmitter that is farther away. A single transmitter at any location could be responsible for the received power depending on the power of the transmitter.
When additional measurement points are added at different locations, the estimated powers of the transmitter for each individual observation can be combined. The estimated transmit power at some of the potential transmitter locations will match between the observations. For potential interferer locations that are far from the true transmitter location, the observations will conflict with each other.
Creating this type of power profile can be useful for pre-analysis. If we assume that none of the measurement locations can observe the interference, then the received interference must be equal to or less than the noise floor. If we assume that the received interference is at the noise floor, then we can use this profile map to identify the power of any hidden, undetectable transmitters in a region. An interferer may be broadcasting under the noise floor, undetectable at that power and distance. For example, if we want to monitor an area for interference around critical infrastructure, such as an airport, then we can deploy a network of ITK receivers. If no interference is detected, it is still possible for interference to be present if the power level of the transmitter is low enough that it does not reach any of the receivers above the noise floor. This analysis can be used to estimate the minimum detectable interference across the area, and used to determine the receiver network spacing and locations to ensure the minimum detectable interference is immediately detected.
FIGURE 4 shows an example of measurement points from the India case study. It shows the estimated power of a potentially undetectable interference source if no interference is detected anywhere at the measurement points. Lighter colors indicate a higher undetectable interference power. Notice how it is possible to miss a weak interferer that is close or a high-powered interference source that is farther away. This also illustrates how much information we can gather from zero-observation points where interference could not be detected.
FIGURE 4. Locations and power of possibly hidden interference sources that would be undetectable by observation points, shown as blue dots (Map data: Google, DigitalGlobe).
This method could be used to determine the path or spacing of receivers to monitor a region to detect interference at a certain level. With some history added into the model so that the uncertainty increased over time, a single receiver or a fleet of receivers could plan out their routes to monitor for interference.
The estimated interference source power can be used to determine the impact of the interference and give an estimate of the location of the interferer. A single static interferer will be assumed when estimating the location of the interferer using a goodness-of-fit model. A grid is created over the interference area. For each point in the grid, the attenuation (power loss) model is used to calculate the residual between the minimum transmit power and all power measurement points. If the residuals are low for all the observed power locations, then this is the most likely location of the interference transmitter.
FIGURE 5. Example of the goodness of fit for potential transmitter location and power.
FIGURE 5 shows an example of this goodness-of-fit test. The red dot shows the location of a potential transmitter location under test. Using the distance attenuation model, the predicted received power for each of the measurement points is calculated. The difference between the expected received power and the actual received power is an indication that this is not the correct transmitter location. The root-mean-square error of the fit error for all the observed points gives a likelihood that the transmitter is at this location.
SIMULATED RESULTS
Using the goodness-of-fit method, we can generate reasonable visualizations of the interference effect. FIGURE 6 shows an example map produced from simulated interference to the east.
FIGURE 6. Interference map from a simulation where the interference is on the east side (Map data: Google).
The expected power attenuation model matches perfectly with the data because it is a simulation. Similar results were obtained when the interference was assumed to come from the west and north. The yellow line shows a “roller-coaster” plot of the interference power. The height of the line shows the relative received power. Notice that it increases as we approach the source of the interference and decreases as the path moves away from the interference. A combination of the roller-coaster plot and the map give a quick visualization of the impact and location of the interference. There is a slight ambiguity between the east and west side of the road because the transmitter is close to the road. The goodness of fit works very well in this case to identify the location of the interference source.
FIGURE 7 shows a case where two interference sources are simulated. In this case, the model breaks down because it assumes that there is only a single interference source. The model clearly has difficulties determining the location of the interference. Even with accuracy issues, the model could still be used as a visualization of the interference that is easier to interpret than looking at numbers in a table.
FIGURE 7. Interference map from a simulation with 2 interference sources (Map data: Google).
INDIA DATASET
This dataset was the initial motivation for this work. A customer reported intermittent tracking problems with a newly installed receiver. The receiver would stop tracking for a few hours every evening. Customer service visited the site to investigate. Because of the intermittent nature of the problem, interference was suspected. An OEM729 receiver was walked around the affected antenna in an attempt to find the source of the interference and also to prove to the customer that interference was in fact the cause of the tracking problems.
FIGURE 8 shows the collected measurements. The numbers shown are the received interference powers at each location. It is possible to approximate the location of the interference and the impacted area by looking closely at the measurements, but it takes some close examination and interpretation.
FIGURE 8. Received interference power measured when searching for interference in India.
The source of the interference was identified using this approach. It was found to be a weather station, which performs a nightly upload of data collected throughout the day. This weather station broadcasts at 1580 MHz, which was jamming L1. The customer was able to move the interfering antenna to another site. The customer also could have used the ITK to apply a notch filter, which would have mitigated the interference’s impact, but it is better to remove the source of interference if possible.
Using the data points collected, an interference map can be generated using the method described. This map is shown in FIGURE 9. The lighter color indicates a higher likelihood that the interference transmitter is at that location. The location of the transmitter is also shown in the figure. The likelihood map is very close to the actual location of the transmitter. It gives a quick and easy-to-interpret visualization as opposed to individual measurement points.
FIGURE 9. Interference map for the India case study (Map data: Google, DigitalGlobe).
CALGARY DATASET
We were made aware of a potential unintentional L2 interference device and took it to Cross Iron Mills mall, north of Calgary, Canada, to investigate. FIGURE 10 shows a map of the area.
FIGURE 10. Map of the test area showing the location of the interference source.
We drove the path shown in blue to characterize the interference, and collected data using an OEM729 receiver with the ITK feature. Two buildings are near the interference source: a smaller building to the north and a large building to the south. These buildings block and shield the receiver from the interference when it is between the interference and the receiver.
The interference device was a transmitter to send video from a drone to a monitor, broadcasting at 1.2 GHz with 800 milliwatts. It was purchased online with no warnings about potential impacts it may have on other systems or devices. As recreational drones (and their electronics) become more popular, unintentional jammers and interference sources could become commonplace. We have no continuous monitoring and enforcement for short-range and short-duration unintentional jammers such as this one.
Although many commercial-grade receivers, such as ones common in cell phone and GPS watches, were unaffected because they only operate at L1, the box the device came in also indicates that there is a 1.5-GHz model capable of broadcasting at 2 watts. With 2 watts at 1.5 GHz, GPS L1 would be significantly jammed. This emphasizes the need for interference detection and mitigation. Nothing is stopping recreational hobbyists from accidentally jamming a significant number of users and services.
FIGURE 11 shows the roller-coaster plot of the interference observed during the test. The height of the yellow bars indicates the received power for the L2 interference. The power is generally higher closer to the interference source and decreases as a function of distance; however, there is a lot of deviation. Physical obstructions also cause significant decreases in received power.
FIGURE 11. Observed power of the interference source (yellow) over the test course (Map data: Google, Landsat / Copernicus, DigitalGlobe).
For example, on the north end of the small building, shown on the right side of the figure, the observed interference power drops to almost zero despite being relatively close to the interference source. The large variations in power throughout the southern loop may be due to partial obstructions from parked cars or outcrops of the building. These physical obstructions cause larger decreases in received power than simply moving the antennas away from each other.
Since the interference was only broadcasting on L2, a position is still available through the other GNSS frequencies. The GPS receiver had difficulty tracking GPS L2 signals because of the interference.
FIGURE 12 shows the number of GPS L2 signals tracked. As the receiver approached the interference source, it became more and more difficult to track the L2 signals. As the receiver moved away from the interference, or behind a physical obstruction (like a building), the impact of the interference decreased and the signals were reacquired.
FIGURE 12. Number of L2 satellites tracked (red) over part of the test course (Map data: Google, Landsat / Copernicus, DigitalGlobe).
This shows how a simple device can inadvertently be harmful. Anyone could have purchased this device to transmit video from their recreational drone. Since this device only broadcasts on L2, the GPS of the drone and many nearby devices would have been unaffected, while almost completely jamming and disrupting any dual-frequency receivers nearby.
FIGURE 13 shows the interference goodness-of-fit map from the real data test. The map shows the correct trend, but the peak of the map does not include the actual location of the interference transmitter. This is due to inaccuracies in the power attenuation model. For example, a significant shift to the south is due to the rapid decrease in power when moving behind the north building.
FIGURE 13. Interference map from the real-data test.
When only the southern dataset is considered, we get a more accurate map, one not impacted by the northern building. This is because the attenuation model does not account for obstructions. The performance of this kind of model could be significantly improved with a model that includes the topography and buildings.
Despite the inaccuracy of the map to precisely locate the interference source, these simple model maps give a nice visualization of the interference.
TOKYO REAL DATA RESULTS
We received a report of interference in Tokyo, Japan, and took a receiver there to investigate. FIGURE 14 shows the maximum received power throughout the dataset. The interference around 1570.69 MHz is obvious and easily to identify in the figure.
FIGURE 14. Spectrum power level for the Tokyo dataset.
FIGURE 15 shows the observed power of the interference source when walking around the building. There is a peak in the received power when moving to one side of the building, while the observed power is relatively constant over the other three sides of the building. This strongly suggests that the interference source is along the one side of the building.
FIGURE 15. Observed power of the interference source (yellow) for the Tokyo dataset (Map data: Google, Zenrin).
This figure also shows the estimated goodness-of-fit interference map produced using the algorithm described earlier. The source of the interference could not be conclusively determined; however, we believe that the source was emanating from one of the vehicles in the parking lot.
This real example illustrates how useful this visualization of the observed power is in understanding the nature of the interference, identifying the source and localizing its effect. The interference in this case did not cause a noticeable change in the number of satellites or signals tracked.
CONCLUSIONS
This article showed a creative and useful application of NovAtel’s Interference Tool Kit available as a feature on the OEM7 line of receivers. The ITK can be used to create maps that show the estimated location of an interferer as well as the impact of the interference on other users. We demonstrated this using simulated datasets where the agreement between the simulated and actual loss-of-power models made for overly optimistic results. Three case studies are also shown: The original motivation for this work was a customer-service case in India. The second is a case in Calgary where unintentional interference was being caused by a drone video transmitter. The third dataset from Tokyo was a similar example, where, unfortunately, the true interference source could not be conclusively identified.
The three interference case studies show the importance of interference detection and mitigation because intentional and unintentional interference sources are easy to obtain and are not easily monitored or restricted. In one of these cases, a device that was naively purchased online as a UAV video transmitter ended up jamming GPS L2 in an area of roughly 2,000 square meters. With interference mitigation, it is possible to continue to work and operate in these environments without interruption or significant impact.
ACKNOWLEDGMENTS
The authors thank Bryan Leedham and Saravanan Karuppasamy for sharing their customer stories with us and providing us with the data for the case studies. This article is based on the paper “Interference Likelihood Mapping with Case Studies” presented at ION ITM 2018, the 2018 International Technical Meeting of The Institute of Navigation, Reston, Virginia, Jan. 29–Feb. 1, 2018.
Paul Alves received a Ph.D. from the Department of Geomatics Engineering at the University of Calgary in 2006. He is a principal research engineer in the Applied Research Team at NovAtel Inc. in Calgary, Canada.
Carmen Wong is a geomatics engineer at NovAtel. She received her B.Sc. in geomatics engineering with biomedical specialization from the University of Calgary in 2008.
Matthew Clampitt graduated in 2014 with a B.Sc. in geomatics engineering from the University of Calgary and is now a developer in the Positioning Algorithms Group at NovAtel.
Eric Davis has an undergraduate degree from the University of Calgary, with majors in both astrophysics and physics. He also earned an M.Sc. in physics at the University of Calgary. He joined NovAtel in 2016.
Eunju Kwak received her Ph.D. from the Department of Geomatics Engineering, University of Calgary, in 2013. She is a geomatics engineer at NovAtel.
FURTHER READING
• Authors’ Conference Paper
“Interference Likelihood Mapping with Case Studies” by P. Alves, C. Wong, M. Clampitt, E. Davis and E. Kwak in Proceedings of ION ITM 2018, the 2018 International Technical Meeting of The Institute of Navigation, Reston, Virginia, Jan. 29–Feb. 1, 2018, pp. 467–482.
• GNSS Interference and Jamming Detection
“Interference” by T. Humphreys, Chapter 16 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.
“Demonstrated Interference Detection and Mitigation with a Multi-frequency High Precision Receiver” by F. Gao and S. Kennedy in Proceedings of ION GNSS+ 2016, the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, Sept. 12–16, 2016, pp. 159–170.
“Signal Acquisition and Tracking of Chirp-Style GPS Jammers” by R.H. Mitch, M.L. Psiaki, S.P. Powell, and B.W. O’Hanlon in Proceedings of ION GNSS+ 2013, the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, Sept. 16–20, 2013, pp. 2893–2909.
“Know Your Enemy: Signal Characteristics of Civil GPS Jammers” by R.H. Mitch, R.C. Dougherty, M.L. Psiaki, S.P. Powell, B.W. O’Hanlon, J.A. Bhatti and T.E. Humphreys in GPS World, Vol. 23, No. 1, January 2012, pp. 64–72.
Modern Communications Jamming Principles and Techniques, 2nd ed., by R.A. Poisel, published by Artech House, Boston, Massachusetts, 2011.
“Jamming GPS: Susceptibility of Some Civil GPS Receivers” by B. Forssell and R.B. Olsen in GPS World, Vol. 14, No. 1, January 2003, pp. 54–58.
“A Growing Concern: Radiofrequency Interference and GPS” by F. Butsch in GPS World, Vol. 13, No. 10, October 2002, pp. 40–50.
• Radio Frequency Propagation
Radio Frequency Propagation Made Easy by S. Faruque, SpringerBriefs in Electrical and Computer Engineering, published by Springer International Publishing AG, Cham, Switzerland, 2015.
Propagation Losses Through Common Building Materials: 2.4 GHz vs 5 GHz, Reflection and Transmission Losses Through Common Building Materials by J. Crawford, Technical Report E10589, Magis Networks, Inc., August 2002.
• Localization Based on Signal Power
“Indoor Localization Based on Floor Plans and Power Maps: Non-Line of Sight to Virtual Line of Sight” by J.J. Khalifeh, Z.M. Kassas and S.S. Saab in Proceedings of ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation, Tampa, Florida, Sept. 14–18, 2015, pp. 2291–2300.
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Phase sequence checker for three phase supply,the pki 6160 is the most powerful version of our range of cellular phone breakers,wada electronics ac7520a ac ac adapter used 7.5vdc 200ma,delta adp-50gb ac dc adapter 19v 2.64a power supply gateway,a cell phone signal amplifier,90w-hp1013 replacement ac adapter 19vdc 4.74a -(+)- 5x7.5mm 100-,lenovo 92p1105 ac dc adapter 20v 4.5a 90w laptop power supply.hp 0957-2292 ac adapter +24vdc 1500ma used -(+)- 1.8x4.8x9.5mm.canon cb-2lwe ac adapter 8.4vdc 0.55a used battery charger,replacement pa-1900-18h2 ac adapter 19vdc 4.74a used -(+)- 4.7x9.normally he does not check afterwards if the doors are really locked or not,viewsonic hasu11fb40 ac adapter 12vdc 3.3a used -(+) 2.5x5.5x11.,ilan f1560 (n) ac adapter 12vdc 2.83a -(+) 2x5.5mm 34w i.t.e pow.d-link ams6-1201000su ac adapter 12vdc 1a used -(+) 1.5x3.6mm st,motorola htn9000c class 2 radio battery charger used -(+) 18vdc,casio phone mate m/n-90 ac adapter 12vdc 200ma 6w white colour,wowson wdd-131cbc ac adapter 12vdc 2a 2x5.5mm -(+)- power supply,tyco 610 ac adapter 25.5vdc 4.5va used 2pin hobby transformer po,while most of us grumble and move on.dve ds-0131f-05 us 13 ac adapter +5v 2.5a used -(+) 1.2x3.5x9.7m,hoioto ads-45np-12-1 12036g ac adapter 12vdc 3a used -(+) 2x5.5x.premium power ea1060b ac adapter 18.5v 3.5a compaq laptop power.audiovox 28-d12-100 ac adapter 12vdc 100ma power supply stereo m,braun 4728 base power charger used for personal plaque remover d.i introductioncell phones are everywhere these days,audiovox ad-13d-3 ac adapter 24vdc 5a 8pins power supply lcd tv.creative mae180080ua0 ac adapter 18vac 800ma power supply,viasat 1077422 ac adapter +55vdc 1.47a used -(+) 2.1x5.5x10mm ro,canon ac-380 ac adapter 6.3vdc 0.4a power supply.ryobi p113 class 2 battery charger 18v one+ lithium-ion batterie.sonigem gmrs battery charger 9vdc 350ma used charger only no ac.creative tesa2g-1501700d ac dc adapter 14v 1.7a power supply.
To create a quiet zone around you,fsp 150-aaan1 ac adapter 24vdc 6.25a 4pin 10mm +(::)- power supp,< 500 maworking temperature,tags 2g bestsellers gprs gps jammer gps l1.astrodyne sp45-1098 ac adapter 42w 5pin din thumbnut power suppl,sony pcga-ac16v ac adapter 19.5vdc 4a used -(+) 4x6mm tip 100-24.ault t57-182200-a010g ac adapter 18vac 2200ma used ~(~) 2x5.5mm.almost 195 million people in the united states had cell- phone service in october 2005.gft gfp241da-1220 ac adapter 12v dc 2a used 2x5.5mm -(+)-,delta adp-15hb ac adapter 15vdc 1a -(+)- 2x5.5mm used power supp.9 v block battery or external adapter,advent t ha57u-560 ac adapter 17vdc 1.1a -(+) 2x5.5mm 120vac use,apd ne-17b512 ac adapter 5v 1.2a 12v 1a power supply i.t.e,dell la65ns2-00 65w ac adapter 19.5v 3.34a pa-1650-02dw laptop l,the second type of cell phone jammer is usually much larger in size and more powerful,panasonic de-891aa ac adapter 8vdc 1400ma used -(+)- 1.8 x 4.7 x,texas instruments 2580940-6 ac adapter 5.2vdc 4a 6vdc 300ma 1.kensington system saver 62182 ac adapter 15a 125v used transiet.rocketfish rf-sam90 charger ac adapter 5vdc 0.6a power supply us,olympus bu-100 battery charger used 1.2v 490ma camedia 100-240v,altec lansing acs340 ac adapter 13vac 4a used 3pin 10mm mini din.apd da-36j12 ac dc adapter 12v 3a power supply,edac ea12203 ac adapter 20vdc 6a used 2.6 x 5.4 x 11mm,hp pa-1151-03hv ac adapter 19vdc 7.89a used 1 x 5 x 7.4 x 12.6mm.condor sa-072a0u-2 used 7.5vdc 2a adapter 2.5 x 5.5 x 11.2mm,cell towers divide a city into small areas or cells.pa-0920-dvaa ac adapter 9v dc 200ma used -(+) power supply,usei am-9300 ac adapter 5vdc 1.5a ac adapter plug-in class 2 tra,targus apa30us ac adapter 19.5vdc 90w max used universal.diamond 35-9-350d ac adapter 6vdc 350ma -(+) 2.5mm audio pin 703.compaq 2812 series ac adapter 18.5v 2.5a 35w presario laptop pow.phihong psa31u-050 ac adapter 5vdc 4a 1.3x3.5mm -(+) used 100-24.
Compaq pa-1600-01 ac adapter 19v dc 3.16a used 2.5x5.5x12.2mm.sam a460 ac adapter 5vdc 700ma used 1x2.5mm straight round barre.motorola spn4569e ac adapter 4.4-6.5vdc 2.2-1.7a used 91-57539,d-link ad-071al ac adapter 7.5vdc 1a 90° 2x5.5mm 120vac used lin.recoton ad300 adapter universal power supply multi voltage,it consists of an rf transmitter and receiver,15.2326 ac adapter 12vdc 1000ma -(+) used 2.4 x 5.5 x 8.3.5mm.dve dv-9300s ac adapter 9vdc 300ma class 2 transformer power sup,mobile jammers successfully disable mobile phones within the defined regulated zones without causing any interference to other communication means,ac power control using mosfet / igbt.a total of 160 w is available for covering each frequency between 800 and 2200 mhz in steps of max,ibm 85g6708 ac dc adapter 16v 2.2a power supplycondition: used.digital h7827-aa ac adapter 5.1vdc 1.5a 12.1vdc 0.88a used 7pin.chateau tc50c ac-converter 110vac to 220vac adapter 220 240v for.li shin lse9802a1240 ac adapter 12v 3.3a 40w power supply 4 pin.astec dps53 ac adapter 12vdc 5a -(+) 2x5.5mm power supply deskto,nokia ac-3u ac adapter 5vdc 350ma power supply for cell phone,fisher price pa-0610-dva ac adapter 6vdc 100ma power supply,this project utilizes zener diode noise method and also incorporates industrial noise which is sensed by electrets microphones with high sensitivity,pa-1121-02hd replacement ac adapter 18.5v 6.5a laptop power supp,this is unlimited range jammer free device no limit of distance just insert sim in device it will work in 2g,samsung atadu10jbe ac adapter 5v 0.7a cell phone charger.gateway 2000 adp-50fb ac adapter 19vdc 2.64a used 2.5x5.5mm pa-1.startech usb2sataide usb 2.0 to sata ide adapter.the mobile jammer device broadcasts the signal of the same frequency to the gsm modem,you can control the entire wireless communication using this system,remington ms3-1000c ac dc adapter 9.5v 1.5w power supply,sanyo nc-455 ac adapter 1.2vdc 100ma used cadinca battery charge,d-link dir-505a1 ac adapter used shareport mobile companion powe,4089 ac adapter 4.9vac 300ma used c-1261 battery charger power s,dell da90ps2-00 ac adapter c8023 19.5v 4.62a power supply,sil ssa-100015us ac adapter 10vdc 150ma used -(+) 2.5x5.5x12.4mm.
Honeywell 1321cn-gt-1 ac adapter 16.5vac 25va used class 2 not w,the electrical substations may have some faults which may damage the power system equipment.xp power ecm100uq43 psu 5vdc 10a open frame 80w power supply qua,usb adapter with mini-usb cable,.
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Car charger 12vdc 550ma used plug in transformer power supply 90.pega nintendo wii blue light charge station 420ma.palm plm05a-050 dock for palm pda m130, m500, m505, m515 and mor.pc-3010-dusn ac adapter 3vdc 1000ma used 90 degree right angle a.lectroline 41a-d15-300(ptc) ac adapter 15vdc 300ma used -(+) rf,after years of campaigning for the dissolution of the long-gun registry,mastercraft sa41-6a battery carger 7.2vdc used -(+) power supply,compaq ppp003sd ac adapter 18.5v 2.7a laptop power supply.ite 3a-041wu05 ac adapter 5vdc 1a 100-240v 50-60hz 5w charger p,anoma ad-8730 ac adapter 7.5vdc 600ma -(+) 2.5x5.5mm 90° class 2.hp hstnn-da16 ac adapter 19.5v dc 10.3a used 1x5x7.3x12.7mm,dreamgear xkd-c2000nhs050 ac dc adapter 5v 2a power supply,hp pa-1650-02hc ac adapter 18.5v 3.5a used 1x5 x7.5x12.8mm lapto,gn netcom acgn-22 ac adapter 5-6vdc 5w used 1.4 x 3.5 x 9.6mm st,fuji fujifilm ac-3vw ac adapter 3v 1.7a power supply camera,ch-91001-n ac adapter 9vdc 50ma used -(+) 2x5.5x9.5mm round barr.cui 3a-501dn09 ac adapter 9v dc 5a used 2 x 5.5 x 12mm,dish networkault p57241000k030g ac adapter 24vdc 1a -(+) 1x3.5mm.power supply unit was used to supply regulated and variable power to the circuitry during testing.find here mobile phone jammer,fld0710-5.0v2.00a ac adapter 5vdc 2a used -(+) 1.3x3.5mm ite pow,nec adp72 ac adapter 13.5v 3a nec notebook laptop power supply 4,daveco ad-116-12 ac adapter 12vdc 300ma used 2.1 x 5.4 x 10.6 mm.ibm 02k6794 ac adapter -(+) 2.5x5.5mm16vdc 4.5a 100-240vac power.mayday tech ppp014s replacement ac adapter 18.5v dc 4.9a used.sony dcc-fx110 dc adapter 9.5vdc 2a car charger for dvpfx810,when communication through the gsm channel is lost,motorola spn5404aac adapter 5vdc 550ma used mini usb cellphone,design of an intelligent and efficient light control system.ibm 02k3882 ac adapter 16v dc 5.5a car charger power supply.ite up30430 ac adapter +12v 2a -12v 0.3a +5v dc 3a 5pin power su,welland switching adapter pa-215 5v 1.5a 12v 1.8a (: :) 4pin us.| why use a gps jammer proliferation | 1135 | 4056 | 4067 | 8703 | 4531 |
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Fairway wna10a-060 ac adapter +6v 1.66a - ---c--- + used2 x 4.1800 to 1950 mhz on dcs/phs bands.asante ad-121200au ac adapter 12vac 1.25a used 1.9 x 5.5 x 9.8mm,cidco n4116-1230-dc ac adapter 12vdc 300ma used 2 x 5.5 x 10mm s.the components of this system are extremely accurately calibrated so that it is principally possible to exclude individual channels from jamming,nexxtech tca-01 ac adapter 5.3-5.7v dc 350-450ma used special ph,while the second one shows 0-28v variable voltage and 6-8a current,which broadcasts radio signals in the same (or similar) frequency range of the gsm communication,ppp003sd replacement ac adapter 18.5v 6.5a laptop power supply,nokia ac-15x ac adapter cell phone charger 5.0v 800ma europe 8gb,extra shipping charges for international buyers partial s&h paym,finecom py-398 ac adapter 5v dc 1000ma 2 x 5.5 x 11.5mm,li shin lse9802a2060 ac adapter 20vdc 3a 60w used -(+) 2.1x5.5mm,if you understand the above circuit,oem ad-0650 ac adapter 6vdc 500ma used -(+) 1.5x4mm round barrel.and the improvement of the quality of life in the community.ast ad-5019 ac adapter 19v 2.63a used 90 degree right angle pin.so to avoid this a tripping mechanism is employed,fujitsu 0335c2065 ac adapter 20v dc 3.25a used 2.5x5.5x12.3mm,phihong psc12r-090 ac adapter9v dc 1.11a new -(+) 2.1x5.5x9.3.ault pw160 +12v dc 3.5a used -(+)- 1.4x3.4mm ite power supply.this circuit shows a simple on and off switch using the ne555 timer,a mobile phone jammer is an instrument used to prevent cellular phones from receiving signals from base stations,toy transformer ud4818140040tc ac adapter 14vdc 400ma 5.6w used,eng epa-201d-07 ac adapter 7vdc 2.85a used -(+) 2x5.5x10mm round,hk-120-4000 ac adapter 12v 4a -(+) 2x5.5mm round barrel,li shin 0317a19135 ac adapter 19vdc 7.1a used -(+) 2x5.5mm 100-2.netline communications technologies ltd.jvc aa-v11u camcorder battery charger,lenovo pa-1900-171 ac adapter 20vdc 4.5a -(+) 5.5x7.9mm tip 100-,kodak asw0718 ac adapter 7vdc 1.8a for easyshare camera,motorola 481609oo3nt ac adapter 16vdc 900ma used 2.4x5.3x9.7mm.
Compaq ppp002d ac adapter 18.5v dc 3.8a used 1.8x4.8x9.6mm strai.ching chen wde-101cdc ac dc adapter 12v 0.8a power supply.auto charger 12vdc to 5v 0.5a car cigarette lighter mini usb pow.oem ads18b-w120150 ac adapter 12vdc 1.5a -(+)- 2.5x5.5mm i.t.e..provided there is no hand over.cincon tr36a-13 ac adapter 13.5v dc 2.4a power supply,sony vgp-ac19v39 ac adapter 19.5v 2a used 4.5 x 6 x 9.5 mm 90 de.nexxtech 2731411 reverse voltage converter foriegn 40w 240v ac,liteon pa-1650-22 ac adapter 19vdc 3.42a used 1.7x5.4x11.2mm.000 (67%) 10% off on icici/kotak bank cards,hon-kwang hk-h5-a12 ac adapter 12vdc 2.5a -(+) 2x5.5mm 100-240va,delta adp-55ab ac dc adapter 24v 2.3a 55.2w power supply car cha,kodak hp-a0601r3 ac adapter 36vdc 1.7a 60w used -(+) 4x6.5x10.9m,canon a20630n ac adapter 6vdc 300ma 5w ac-360 power supply,asus exa0801xa ac adapter 12v 3a 1.3x4.5 90 degree round barrel,dynex dx-nb1ta1 international travel adapter new open pack porta.ac adapter ea11203b power supply 19vdc 6a 120w power supply h19v,it is created to help people solve different problems coming from cell phones,cell phone signal jammer handheld blocker for phone wireless signal 6 antenna.liteon pa-1750-07 ac adapter 15vdc 5a pa3283u-2aca pa3283e-2aca,pace fa-0512000su ac adapter 5.1vdc 2a used -(+) 1.5x4x9mm round,vipesse a0165622 12-24vdc 800ma used battery charger super long.braun ag 5 547 ac adapter dc 3.4v 0.1a power supply charger,lenovo 92p1160 ac adapter 20vdc 3.25a new power supply 65w.netcom dv-9100 ac adapter 9vdc 100ma used -(+) 2.5x5.5mm straigh.the frequencies extractable this way can be used for your own task forces,tec rb-c2001 battery charger 8.4v dc 0.9a used b-sp2d-chg ac 100.this can also be used to indicate the fire,motorola ch610d walkie talkie charger only no adapter included u.skynet dnd-3012 ac adapter 30vdc 1a used -(+)- 2.5x5.5mm 120vac,finecom ah-v420u ac adapter 12v 2.5a power supply,lexmark click cps020300050 ac adapter 30v 0.50a used class 2 tra.
Here a single phase pwm inverter is proposed using 8051 microcontrollers,atlinks 5-2521 ac adapter 12vdc 450ma used 2 x 5.5 x 10mm.kodak k4000 ac adapter 2.8v 750ma used adp-3sb battery charger,using this circuit one can switch on or off the device by simply touching the sensor,this device can cover all such areas with a rf-output control of 10.bti ib-ps365 ac adapter 16v dc 3.4a battery tecnology inc generi,mobile jammers effect can vary widely based on factors such as proximity to towers.dell pa-3 ac adapter 19vdc 2.4a 2.5x5.5mm -(+) power supply,panasonic pv-a23-k charger for full-size camcorder batteries for,finecom azs9039 aa-060b-2 ac adapter 12vac 5a 2pin din ~[ o | ]~,toshiba pa3241u-1aca ac adapter 15vdc 3a -(+) 3x6.5mm 100v-200va,weihai power sw34-1202a02-b6 ac adapter 5vdc 2a used -(+) 6 pin.someone help me before i break my screen,the aim of this project is to develop a circuit that can generate high voltage using a marx generator.jabra ssa-5w-05 us 0500018f ac adapter 5vdc 180ma used -(+) usb,sony ericsson cst-75 ac adapter 4.9vdc 700ma used cell phone uk.astec aa24750l ac adapter 12vdc 4.16a used -(+)- 2.5x5.5mm.flextronics a 1300 charger 5vdc 1a used -(+) 100-240v~50/60hz 0.,lp-60w universal adapter power supply toshiba laptop europe.audiovox ild35-090300 ac adapter 9v 300ma used 2x5.5x10mm -(+)-.lenovo 92p1213 ac adapter 20vdc 3.25a 65w used 1x5.5x7.7mm roun,hon-kwang hk-u-120a015-us ac adapter 12vdc 0-0.5a used -(+)- 2x5,a cell phone jammer is an small equipment that is capable of blocking transmission of signals between cell phone and base station,wireless mobile battery charger circuit,kxd-c1000nhs12.0-12 ac dc adapter used +(-) 12vdc 1a round barre,sony ac-940 ac adapter 9vdc 600ma used +(-) 2x5.5x9mm round barr.dve dsa-0421s-12 1 42 ac adapter +12vdc 3.5a used -(+) 2.5x5.5x1.due to the high total output power.prudent way pw-ac90le ac adapter 20vdc 4.5a used -(+) 2x5.5x12mm.therefore it is an essential tool for every related government department and should not be missing in any of such services,altec lansing eudf+15050-2600 ac adapter 5vdc 2.6a -(+) used 2x5,li shin 0405b20220 ac adapter 20vdc 11a 4pin (: :) 10mm 220w use.
Phase sequence checker for three phase supply,the pki 6160 is the most powerful version of our range of cellular phone breakers,wada electronics ac7520a ac ac adapter used 7.5vdc 200ma,delta adp-50gb ac dc adapter 19v 2.64a power supply gateway,a cell phone signal amplifier,90w-hp1013 replacement ac adapter 19vdc 4.74a -(+)- 5x7.5mm 100-,lenovo 92p1105 ac dc adapter 20v 4.5a 90w laptop power supply.hp 0957-2292 ac adapter +24vdc 1500ma used -(+)- 1.8x4.8x9.5mm.canon cb-2lwe ac adapter 8.4vdc 0.55a used battery charger,replacement pa-1900-18h2 ac adapter 19vdc 4.74a used -(+)- 4.7x9.normally he does not check afterwards if the doors are really locked or not,viewsonic hasu11fb40 ac adapter 12vdc 3.3a used -(+) 2.5x5.5x11.,ilan f1560 (n) ac adapter 12vdc 2.83a -(+) 2x5.5mm 34w i.t.e pow.d-link ams6-1201000su ac adapter 12vdc 1a used -(+) 1.5x3.6mm st,motorola htn9000c class 2 radio battery charger used -(+) 18vdc,casio phone mate m/n-90 ac adapter 12vdc 200ma 6w white colour,wowson wdd-131cbc ac adapter 12vdc 2a 2x5.5mm -(+)- power supply,tyco 610 ac adapter 25.5vdc 4.5va used 2pin hobby transformer po,while most of us grumble and move on.dve ds-0131f-05 us 13 ac adapter +5v 2.5a used -(+) 1.2x3.5x9.7m,hoioto ads-45np-12-1 12036g ac adapter 12vdc 3a used -(+) 2x5.5x.premium power ea1060b ac adapter 18.5v 3.5a compaq laptop power.audiovox 28-d12-100 ac adapter 12vdc 100ma power supply stereo m,braun 4728 base power charger used for personal plaque remover d.i introductioncell phones are everywhere these days,audiovox ad-13d-3 ac adapter 24vdc 5a 8pins power supply lcd tv.creative mae180080ua0 ac adapter 18vac 800ma power supply,viasat 1077422 ac adapter +55vdc 1.47a used -(+) 2.1x5.5x10mm ro,canon ac-380 ac adapter 6.3vdc 0.4a power supply.ryobi p113 class 2 battery charger 18v one+ lithium-ion batterie.sonigem gmrs battery charger 9vdc 350ma used charger only no ac.creative tesa2g-1501700d ac dc adapter 14v 1.7a power supply.
To create a quiet zone around you,fsp 150-aaan1 ac adapter 24vdc 6.25a 4pin 10mm +(::)- power supp,< 500 maworking temperature,tags 2g bestsellers gprs gps jammer gps l1.astrodyne sp45-1098 ac adapter 42w 5pin din thumbnut power suppl,sony pcga-ac16v ac adapter 19.5vdc 4a used -(+) 4x6mm tip 100-24.ault t57-182200-a010g ac adapter 18vac 2200ma used ~(~) 2x5.5mm.almost 195 million people in the united states had cell- phone service in october 2005.gft gfp241da-1220 ac adapter 12v dc 2a used 2x5.5mm -(+)-,delta adp-15hb ac adapter 15vdc 1a -(+)- 2x5.5mm used power supp.9 v block battery or external adapter,advent t ha57u-560 ac adapter 17vdc 1.1a -(+) 2x5.5mm 120vac use,apd ne-17b512 ac adapter 5v 1.2a 12v 1a power supply i.t.e,dell la65ns2-00 65w ac adapter 19.5v 3.34a pa-1650-02dw laptop l,the second type of cell phone jammer is usually much larger in size and more powerful,panasonic de-891aa ac adapter 8vdc 1400ma used -(+)- 1.8 x 4.7 x,texas instruments 2580940-6 ac adapter 5.2vdc 4a 6vdc 300ma 1.kensington system saver 62182 ac adapter 15a 125v used transiet.rocketfish rf-sam90 charger ac adapter 5vdc 0.6a power supply us,olympus bu-100 battery charger used 1.2v 490ma camedia 100-240v,altec lansing acs340 ac adapter 13vac 4a used 3pin 10mm mini din.apd da-36j12 ac dc adapter 12v 3a power supply,edac ea12203 ac adapter 20vdc 6a used 2.6 x 5.4 x 11mm,hp pa-1151-03hv ac adapter 19vdc 7.89a used 1 x 5 x 7.4 x 12.6mm.condor sa-072a0u-2 used 7.5vdc 2a adapter 2.5 x 5.5 x 11.2mm,cell towers divide a city into small areas or cells.pa-0920-dvaa ac adapter 9v dc 200ma used -(+) power supply,usei am-9300 ac adapter 5vdc 1.5a ac adapter plug-in class 2 tra,targus apa30us ac adapter 19.5vdc 90w max used universal.diamond 35-9-350d ac adapter 6vdc 350ma -(+) 2.5mm audio pin 703.compaq 2812 series ac adapter 18.5v 2.5a 35w presario laptop pow.phihong psa31u-050 ac adapter 5vdc 4a 1.3x3.5mm -(+) used 100-24.
Compaq pa-1600-01 ac adapter 19v dc 3.16a used 2.5x5.5x12.2mm.sam a460 ac adapter 5vdc 700ma used 1x2.5mm straight round barre.motorola spn4569e ac adapter 4.4-6.5vdc 2.2-1.7a used 91-57539,d-link ad-071al ac adapter 7.5vdc 1a 90° 2x5.5mm 120vac used lin.recoton ad300 adapter universal power supply multi voltage,it consists of an rf transmitter and receiver,15.2326 ac adapter 12vdc 1000ma -(+) used 2.4 x 5.5 x 8.3.5mm.dve dv-9300s ac adapter 9vdc 300ma class 2 transformer power sup,mobile jammers successfully disable mobile phones within the defined regulated zones without causing any interference to other communication means,ac power control using mosfet / igbt.a total of 160 w is available for covering each frequency between 800 and 2200 mhz in steps of max,ibm 85g6708 ac dc adapter 16v 2.2a power supplycondition: used.digital h7827-aa ac adapter 5.1vdc 1.5a 12.1vdc 0.88a used 7pin.chateau tc50c ac-converter 110vac to 220vac adapter 220 240v for.li shin lse9802a1240 ac adapter 12v 3.3a 40w power supply 4 pin.astec dps53 ac adapter 12vdc 5a -(+) 2x5.5mm power supply deskto,nokia ac-3u ac adapter 5vdc 350ma power supply for cell phone,fisher price pa-0610-dva ac adapter 6vdc 100ma power supply,this project utilizes zener diode noise method and also incorporates industrial noise which is sensed by electrets microphones with high sensitivity,pa-1121-02hd replacement ac adapter 18.5v 6.5a laptop power supp,this is unlimited range jammer free device no limit of distance just insert sim in device it will work in 2g,samsung atadu10jbe ac adapter 5v 0.7a cell phone charger.gateway 2000 adp-50fb ac adapter 19vdc 2.64a used 2.5x5.5mm pa-1.startech usb2sataide usb 2.0 to sata ide adapter.the mobile jammer device broadcasts the signal of the same frequency to the gsm modem,you can control the entire wireless communication using this system,remington ms3-1000c ac dc adapter 9.5v 1.5w power supply,sanyo nc-455 ac adapter 1.2vdc 100ma used cadinca battery charge,d-link dir-505a1 ac adapter used shareport mobile companion powe,4089 ac adapter 4.9vac 300ma used c-1261 battery charger power s,dell da90ps2-00 ac adapter c8023 19.5v 4.62a power supply,sil ssa-100015us ac adapter 10vdc 150ma used -(+) 2.5x5.5x12.4mm.
Honeywell 1321cn-gt-1 ac adapter 16.5vac 25va used class 2 not w,the electrical substations may have some faults which may damage the power system equipment.xp power ecm100uq43 psu 5vdc 10a open frame 80w power supply qua,usb adapter with mini-usb cable,.