2021/07/31
Part 1 of a Two-Part Story. Read Part 2 here.
Cover: GPS World
By Bradford W. Parkinson and Stephen T. Powers, with Gaylord Green, Hugo Fruehauf, Brock Strom, Steve Gilbert, Walt Melton, Bill Huston, Ed Martin, James Spilker, Fran Natali, Joe Strada, Burt Glazer, Dick Schwartz, Tom Stansell, and others
The original system study, the key innovations, and the forgotten heroes of the world’s first — and still greatest — global navigation satellite system. True history, told by the people who made it. Part One of a Two-Part Special Feature.
The stealth utility: over the past 30 years, a new entity has steadily and stealthily crept into the fabric of worldwide society, creating capabilities and dependencies that did not exist before. This utility is known as the Global Positioning System, or GPS. With more than a billion GPS receivers in use, this stunning achievement has truly revolutionized the way the world functions in the 21st century. Virtually every cell-phone system relies on GPS for timing. Almost every ship and aircraft carries multiple GPS receivers to provide positioning information. Other applications span military targeting, transportation, object tracking, and resource identification. Today, the loss of GPS signals would have catastrophic consequences.
How did GPS come into being? What technologies were essential to its success? Who developed those technologies? Recently a number of GPS histories have appeared that are very inaccurate on these subjects. Our purpose in writing this account is to set the record straight, and in so doing to give credit to many of the original developers of GPS whose contributions have somehow been forgotten. Throughout this article you will find their names highlighted. Space does not permit us to name the many other individuals who deserve enormous credit for the subsequent refinement and invention of new GPS applications.
Figure 1 gives a summary view of the history of U.S. satellite-based navigation, particularly GPS. Details of the Russian GLONASS and the European Galileo systems are not included as they arrived later, and generally mimicked the GPS development albeit with their own, locally developed detailed designs.
Figure 1. The eras of satellite navigation. (Credit: Bradford W. Parkinson and Stephen T. Powers)
Dr. Richard Kershner, who led the development of Transit. On his left, young Col. Bradford Parkinson, who led the development of GPS. (Credit: Bradford W. Parkinson and Stephen T. Powers)
This history focuses on the period up to about 1980, when GPS was approved for full-scale development. Between that time and the date that GPS was declared fully operational, April 27, 1995, many additional contributions were made. The system withstood several early attempts by the Air Force to cancel it entirely. Fortunately, those attempts did not succeed, and the Air Force now fully embraces GPS as an essential part of virtually every weapon system in the inventory.
We call this a tribute to the almost-forgotten people whose intellectual labor and skill initially developed GPS. As we unveil this story, we will point out the original — and critical — system study, the 1966 Woodford/Nakamura Report, that became the essential blueprint for GPS. Many people are unaware of this study since, in its original form, it was classified U.S. Department of Defense (DoD) Secret. It was not declassified until August 1979, more than a year after the first launch of a GPS operational satellite in February 1978.
We also intend to describe and justify the key innovation that enabled the system. This keystone technology is the GPS code-division multiple-access (CDMA) signal. While CDMA was necessary for GPS success, it was by no means sufficient.
We will also define and describe the five major original challenges that had to be met to achieve the success that GPS now enjoys; that will come in the second installment of this history, to appear in next month’s issue.
Mathematician Bill Guier (l) and physicist George Weiffenbach (r), told APL Research Center director Frank T. McClure (c), about their success using Doppler tracking for satellites. “McClure’s brain started going into fast forward,” remembered John Dassoulas. “Knowing the navigational challenges the U.S. Navy faced, McClure said, ‘Well, if you can find out where the satellite is, you ought to be able to turn that problem upside down and find out where you are.’” (Credit: Bradford W. Parkinson and Stephen T. Powers)
GPS Predecessors: Transit
On October 4, 1957, the entire world was amazed by the launch of Russia’s Sputnik satellite. The American public greeted this event with both apprehension and curiosity. Both the Army and Navy had been quietly working on satellite projects for some years. In an attempt to catch up, the United States had a spectacular failed launch when the Naval Research Laboratory’s (NRL’s) TV-3 crashed on December 6, 1957. On January 31, 1958, the United States Army launched a grapefruit-sized satellite, Explorer 1. The NRL then achieved success with the launch of TV-4, renamed Vanguard-1, on March 27, 1958.
In 1958, the Applied Physics Laboratory (APL) of Johns Hopkins University employed an extremely competent team of engineers and scientists. Two of those scientists, Drs. William Guier and George Weiffenbach, began to study the orbits of the new Sputnik satellites. The satellites were broadcasting a continuous tone signal. Their velocity relative to the ground created a Doppler shift of that signal that was unique. After some innovative work, Guier and Weiffenbach discovered they could determine the Sputnik’s orbit with a single pass of the vehicle.
At that point Frank McClure of APL made a very creative suggestion: Why not turn the problem upside down? Using a known satellite position, a navigator could determine his location anywhere in the world after receiving and processing the satellite signal for 15 minutes. His insight became the basis for the Navy’s Transit satellite program, also known as the Navy Navigation Satellite System (Figure 2).
This pioneering system was developed under the leadership of Dr. Dick Kershner, head of the Space Department of APL. Transit’s main purpose was to provide position updates to the United States submarine ballistic-missile force then under development. These submarines were a major deterrent during the Cold War. Transit was first tested in 1960, and by 1964 the system was fully operational. Under Kershner, APL rapidly mastered the art of building long-life satellites. In fact, two of the vehicles continued operation for more than 20 years.
Figure 2. The Transit birdcage of operational orbits. (Credit: Bradford W. Parkinson and Stephen T. Powers)
Transit was a relatively small satellite that initially used solar power and gravity-gradient stabilization (Figure 3). It provided a position fix every few hours; fixes took 10 to 16 minutes of exposure of the submarine’s antenna on the surface. It achieved 25-meter accuracy, but only in two dimensions. Further, if the user was moving, accurate velocity measurement was critical: a 1-knot error would produce a 0.2-nautical mile position error.
All Navy ships could use the system, and in 1967 Transit was offered to the civilian community by Vice President Hubert Humphrey. Magnavox became the principal developer of civil user sets with Tom Stansell as an early expert in the technology.
Contributions to GPS. The Transit program developed a technique essential for GPS: the use of two frequencies to calibrate the time delay of the radio signal induced by the ionosphere. This dual-frequency technique was incorporated into GPS to attain the highest positioning accuracy. In addition, Transit also pio
neered the accurate prediction of satellite orbits, another essential GPS technology. Orbit prediction will be highlighted later, as one of the five fundamental challenges that faced GPS system designers.
In 1974, Transit made a further contribution to GPS development that we discuss in that approximate timeframe.
Figure 3. A Transit satellite showing the gravity-gradient boom that kept the antennas pointing at the earth. (Credit: Bradford W. Parkinson and Stephen T. Powers):
Program 621B
As early as 1962, Dr. Ivan Getting, president of the Aerospace Corporation, saw the need for a new satellite-based navigation system. He envisioned a more accurate positioning system that would be available in three dimensions, 24 hours a day, seven days a week. He had direct access to the highest levels of the Pentagon and was a tireless advocate for his vision.
Getting’s energy and foresight in the early 1960s were essential to gaining Air Force support to study system alternatives. As a result, the Air Force formed a new satellite navigation program that was later named 621B. Getting’s efforts were recognized in 2002 when he shared the Charles Stark Draper Prize of the National Academy of Engineering with Bradford Parkinson.
By 1962, engineers at Aerospace, under Air Force sponsorship, were heavily immersed in studying the system aspects of a new navigational satellite system. From 1964 to 1966, Aerospace carried out an extensive, formal system study whose principal authors were James Woodford and Hideyoshi Nakamura, both highly regarded space-systems engineers.
Their work was summarized as a DoD secret briefing in August 1966. As a result of the classification, it was unavailable to anyone outside the project until 13 years later, in 1979, when it was finally declassified (figure 4).
The Woodford/Nakamura Report was a complete system study that examined these issues:
capabilities and limitations of then-current DoD navigation systems;
tactical applications and utility of improved positioning accuracy;
comprehensive analysis of alternative system configurations and techniques for positioning, using satellites.
The report concluded with a set of recommendations for advanced technology development for navigation satellite programs.
Figure 4. Front page of the seminal GPS system study performed from 1964 to 1966 by USAF 621B Program. Originally classified secret, it was not declassified until after the initial GPS satellite had been launched. This was the essential foundation to the GPS System design. (Credit: Bradford W. Parkinson and Stephen T. Powers)
The detailed analysis of possible passive navigation techniques was extremely important. It pointed out that the most capable passive-ranging design, called triple delta rho, would eliminate the need for an extremely stable clock in the user equipment and would provide three-dimensional positioning. (In this article we use clock, oscillator, and frequency standard interchangeably. The timing community makes some distinctions among these words, but for purposes of this history the distinctions are not particularly important.) This later was selected as the fundamental GPS system concept of ranging to four satellites simultaneously.
Key conclusions of the 1966 study advocated:
passive ranging from the satellites (the issue was which ranging signal to use)
atomic clocks in space, and a technology program to develop space hardened atomic clocks
further system studies as well as experimental demonstrations.
Since the full survey of alternative system configurations was extremely important in selecting an optimum system configuration, we reproduce the summary in figure 5. Note that the “Computation Performed by User” is split into two columns. Focus on the columns of the one-way passive ranging techniques with the red outline. Inside, there are two “user boxes,” one with A and one with X. The A shows the user needs an atomic clock. The X shows the user needs only a crystal clock. The option later selected for GPS is designated as G. This technique is the 3Δρ (triple delta rho, or four satellites) that eliminated the need for the user atomic clock, and provided three-dimensional positioning (really four-dimensional since it also captured time).
In October 1970, more than four years after the completion of this study, Roger Easton of NRL applied for a patent on the two-satellite, ρ-ρ technique (option N) that required an atomic clock for the user and was only two-dimensional. The patent (U.S. 3,789,409) was granted in 1974, a year after the three-dimensional design of the GPS system had already been defined in the Lonely Halls Pentagon meeting to be described later.
Figure 5. Summary of the alternative satellite-based navigation techniques from the1964–66 USAF/621B study. The most capable option, circled in green, became the basis for the White Sands prototyping and testing, and then evolved into GPS. NRL applied for a patent on the less capable technique (red line) four years after the Woodford/Nakamura Study was completed. (Credit: Bradford W. Parkinson and Stephen T. Powers)
Credit: Bradford W. Parkinson and Stephen T. Powers
More 621B Studies. From 1966 to 1972, program 621B continued with trade-off studies including: signal modulation, user data processing techniques, orbital configuration, orbital prediction, receiver accuracy, error analysis, system cost, and comprehensive estimates of the tactical mission benefits. More than 90 reports completed by USAF/Aerospace during this period remain available in the Aerospace Corporation library.
PRN or CDMA Signal Structure. Of these studies, the most important were those aimed at selecting the best passive ranging technique for the navigation signal. By 1967, it appeared that the best technique was a variation of a new communications modulation known as CDMA. Pioneering this signal were several outstanding scientists, Dr. Fran Natali and Dr. Jim Spilker (both of Philco-Ford), and Dr. Charlie Cahn (of Magnavox).
Credit: Bradford W. Parkinson and Stephen T. Powers
This signal has many names. In addition to CDMA, it is sometimes called spread spectrum, since the energy of the signal was spread over a wide range of radio frequencies. It is also sometimes called PRN or pseudorandom noise because the encoded (and repeated) sequence appears to be random transitions of +1 and -1.
The name code-division is used because each satellite is assigned its own coded signal. Each was a binary (digital) sequence selected to be uncorrelated with other signals and also uncorrelated with time shifts of the signal itself. The expected, powerful advantage of this technique was that all satellites would broadcast on exactly the same frequency. It would clearly lend itself to digital signal processing. Furthermore, and very important, any time-shifts induced by the receiver for the various satellite signals would be effectively eliminated.
However, several significant questions concerning CDMA still needed resolution. These included:
Could such a signal be easily acquired in the face of time uncertainty and Doppler shifts?
Was there a technique to encrypt the military signal so that unauthorized users could not gain access?
How would the c
odes be easily selected to avoid a false lock and also allow additional satellites to be added without interfering with existing satellite signals?
Would the anticipated complexity of the receiver drive costs to unacceptable levels?
Was the signal resistant to accidental or deliberate interference?
Could this signal accommodate communication capability for satellite location, satellite clock correction, and other parameters?
Fortunately, in 1967 a technique for selecting orthogonal codes was invented by an accomplished applied mathematician, Dr. Robert Gold of the Magnavox Corp. Naturally these are now known as the Gold codes. His solution resolved the third CDMA issue stated above.
White Sands Tests. To address the remaining issues, the 621B program developed two prototype versions of CDMA navigation receivers (Magnavox and Hazeltine) for testing at the White Sands Missile Range (WSMR). For these initial 1971 tests, 621B arranged four transmitters in a configuration known as the inverted range. (Interestingly, the more capable receiver was the MX-450 that was only on loan from Magnavox.) These transmitters broadcast CDMA signals from locations that were similar to a satellite configuration except that they were broadcast from the ground. For the simulation of satellite geometry, a balloon-based transmitter was also included for the aircraft-landing tests. Al Gillogly of Aerospace spent many hours installing and troubleshooting the test configuration.
Al Gillogly, Aerospace engineer (left), setting up the critical tests of prototype GPS receivers at WSMR in 1970. (Credit: Bradford W. Parkinson and Stephen T. Powers)
By 1972, program 621B had successfully proven the effectiveness and accuracy of the CDMA signal by demonstrating that such a configuration would achieve 5-meter, 3-dimensional navigation accuracy. Much credit for the painstaking analysis of these results should go to Bill Fees of Aerospace who wrote the final detailed test report. These test results answered most of the remaining issues regarding the CDMA signal.
The tests also confirmed the power of the modulated signal by showing that all satellite signals could, indeed, be received simultaneously on the same frequency. These tests also corroborated the expectation that ranging to four satellites eliminated the need for a highly precise user atomic clock, while still supporting full, three-dimensional navigation. This became an extremely important feature of GPS. If each user had required an atomic-clock class frequency-standard, no inexpensive user equipment could have been produced within the technology horizon visible at that time. This is still true today.
All this evidence supported CDMA as the passive ranging signal of choice and was available to the Air Force’s 621B team when the system configuration was selected at the September 1973 Pentagon meeting that will be discussed later.
621B Demo, Operational Differences. From the time of the 1966 Woodford/Nakamura study on, the Air Force and Aerospace advocated the use of atomic clocks in the operational satellites with the modulation also originating in the satellites. There were two significant risks to placing atomic clocks in the satellites: First, the technology readiness risk: no hardened atomic clocks had yet been designed and flown; and second, the political/budgeting risk associated with gaining approval for a development/demonstration program for the full capability. The Air Force developed a plan to reduce both risks.
In late 1968, the Air Force’s NavSat program in the Plans Office (XR) at the Space and Missile Systems Organization (SAMSO) was redesignated as 621B. All of the various proposals that went forward from SAMSO to Headquarters came henceforth from the 621B office in XR. This included a proposal in early 1972 to deploy a four-satellite demonstration system. This proposal addressed both risks. It would reduce the technology readiness risk in the clocks by launching simple L-band transponders. At the same time, it would save substantial money, thereby reducing the political/budgeting risk.
QZSS (Credit: Bradford W. Parkinson and Stephen T. Powers)
In many circles, this proposal was erroneously thought of as 621B because it came from that office, but in fact, the operational concept for 621B never contemplated or advocated using transponders in the final operational system. Transponders had been rejected for the operational system because they could be easily jammed from the ground. Such a jamming signal would overpower the transponder and steal all of the transmitted energy away from the transponded navigational signal. This enemy jamming would shut down the entire system, clearly an unacceptable risk.
Proposed Initial Constellation. To demonstrate four-satellite, passive ranging capability, 621B had studied a number of orbital configurations, including geo-synchronous and lower inclined orbits. The program proposed to place a constellation of three or four synchronous satellites in orbits over the United States. This array would allow extended periods of four-satellite testing without committing to a full global employment. If this demonstration were successful, the next step would have been to add three more longitudinal sectors, each with its own array. Again, the principal redeeming feature of this approach was that there was some hope of it being funded. The Air Force in the Pentagon placed enormous pressure on the 621B program to come up with the absolutely cheapest way to demonstrate the four-satellite approach.
This proposed constellation design was a reasonable compromise, given the boundary conditions of a four-satellite demonstration and absolutely minimal cost. It is interesting that the Japanese, with a requirement to supplement GPS with satellite signals to improve coverage in urban areas (where there are high shading angles), have designed a very similar constellation. The Japanese configuration is intended to improve coverage restricted to their longitudinal sector of the globe. The new system is called Quasi-Zenith Satellite System (QZSS), and the Japanese appear to be well on the way to fielding it.
Timation and NRL
In 1964, the U.S. Navy initiated a second satellite program, named Timation, under the direction of Roger L. Easton, Sr., a long-time member of the NRL staff. The NRL’s Timation project was aimed at exploring techniques for passive ranging to satellites, as well as time transfer between various timing centers around the world. This project ran parallel to, and was in competition with, the Air Force Program. It subsequently developed a number of experimental satellites, the first of which was called Timation 1. This small satellite, weighing 85 pounds and producing 6 watts of power, was launched on May 27, 1967.
Timation 1, developed by NRL, was a miniaturized, innovative design. The quartz clock was less stable than expected, apparently due to temperature and cosmic-ray effects. (Credit: Bradford W. Parkinson and Stephen T. Powers)
The key feature of Timation 1 was that it included a very stable quartz clock. The fundamental ranging technique was to synchronize a clock at the user’s location with the clock on the satellite and use a passive-ranging signal structure called side-tone ranging. By 1968, NRL demonstrated single-satellite position fixes, accurate to about 0.3 nautical miles, that required about 15 minutes of data collection (Global Positioning System, Volume 1, chapter “Navigation Technology Program,” R.L. Easton, p.16). NRL engineers encountered two significant problems during their testing: sol
ar radiation caused shifts in the clock’s frequency, and ionospheric group delay created ranging errors.
The NRL launched a second satellite, Timation 2, into a 500-mile orbit on September 30, 1969. To calibrate ionospheric group delay, the satellite broadcast on two frequencies very similar to the technique pioneered by the Transit program. Its quartz oscillator was expected to be somewhat more stable, about one part in 1011. Again, a large frequency shift was observed in the clocks that was finally traced to a solar proton storm. NRL was able to demonstrate ranging accuracies of approximately 200 feet to a fixed location.
Timation NTS-1. The last satellite in the original Timation series was launched in July 1974. By that time the Timation program had been placed under the GPS Joint Program Office in Los Angeles, reporting through the Navy Deputy, Cdr. Bill Huston, to the Program Director Col. Bradford Parkinson. The JPO had renamed the satellite as Navigation Technology Satellite (NTS-1). The gross weight had been increased to 650 pounds with a power requirement of 125 watts. This satellite, developed by Pete Wilhelm of NRL, was placed at an orbital altitude of 7,500 nautical miles.
Timation NTS-1 carried two slightly modified commercial rubidium clocks. Unfortunately, attitude-stabilization problems induced temperature variations that masked any quantitative performance evalulation. The atomic clocks were not useful as prototypes for GPS. (Credit: Bradford W. Parkinson and Stephen T. Powers)
The NTS satellites were strictly technology-testing satellites. For many reasons, they had no role in the development of the operational satellites by the JPO and Rockwell. The latter were operational satellites and were called NDS, for Navigation Development Satellites. They were the only ones used in the operational testing during phase I of GPS.
NTS-1 included two small, lightweight rubidium oscillators as clocks. A German commercial company called Efratom had independently developed these models. Amazing at the time, they only consumed about 13 watts of power and weighed some four pounds each. Further Efratom involvement will be pointed out later. While NRL made some electronic modifications, the modified clocks were not in any sense able to withstand the radiation of the GPS orbits. The NTS-1 clocks were certainly not prototypes for the Rockwell clocks that were developed directly for the JPO and flown on the first block of GPS satellites.
NRL tests showed that the modified rubidium clocks had an unacceptable level of sensitivity to temperature variations. Al Bartholemew of the NRL later wrote that “the lack of attitude stabilization system on NTS-1 resulted in large temperature variations which ultimately masked any quantitative evaluation of rubidium standard performance.” (Global Positioning System, volume 1, chapter “Satellite Frequency Standards,” C.A. Bartholomew, p. 25.) This apparently occurred because the satellite used a two-axis gravity gradient stabilization system that does not function well at these altitudes. The Navigation Development Satellites (NDS) satellites, later developed by the JPO, avoided this by developing a new, full three-axis, attitude-control system. NTS-1 carried other space technology demonstrations including highly efficient solar cells.
Later, NRL developed a second (and last) satellite (NTS-II) for the GPS Program Office, after the Pentagon had approved the project in December 1973. The vehicle included two modified cesium beam oscillators developed by Frequency and Time Systems Inc. (FTS) of Danvers Massachusetts. The key atomic clock developer was the engineer and creative entrepreneur Robert Kern. This clock showed great initial promise but it was not yet a space prototype in terms of radiation hardening and parts life. In addition, the JPO provided a Rockwell-developed navigation payload for NTS-II that the JPO had developed for the operational GPS satellites. This would allow the NRL satellite to broadcast the GPS CDMA signal.
Credit: Bradford W. Parkinson and Stephen T. Powers
NTS-II was launched on June 23, 1977, from Vandenberg Air Force Base. Originally it was hoped that NTS-II would be a part of the initial GPS test constellation. It could then have supplemented the satellites being developed by Rockwell, providing another passive ranging signal for the user equipment tests at Yuma Proving Ground. Unfortunately, the NRL ranging transmitter in NTS-II failed prior to the launch of the first JPO NDS satellites, rendering the NRL satellite unusable for the Yuma Proving Ground testing. “Of the two experimental cesium standards carried on NTS-II,” Ron Beard of NRL wrote, “one experienced a power supply failure after a period of satisfactory operation.” It is known that the other cesium clock continued to operate for over a year, but quantitative drift rates on orbit were never available. As a result of these failures, the cesium clock tests were inconclusive. (Proceedings of the IEEE 43rd Annual Symposium on Frequency Control, 1989, R.L. Beard, p. 276.) Only tests with the first four JPO/Rockwell satellites were available to support the full-scale development approval on June 5, 1979.
For the next step, NRL defined a radiation-hardening program and contracted with FTS to develop a hardened cesium clock. This new clock was flown on the fourth operational GPS satellite (NDS 4, launched December 10, 1978). Unfortunately, the clock suffered a premature failure of the power supply after only 12 hours of operation. FTS soon found the root cause and fixed the design. Beginning with NDS 5, the on-board cesium clocks performed well and were equal or better in stability to the Rockwell rubidium oscillators.
Competition, Lonely Halls
By 1972, a few Pentagon authorities had recognized that a new satellite-based navigation system would be a valuable asset with multiple military applications. Literally hundreds of positioning and navigation systems in use by the DoD were expensive to maintain and upgrade. Obviously, a single replacement system offered significant cost savings. Unfortunately, the two competing concepts from 621B and NRL apparently confused the decision-makers. Discussions grew very acrimonious at times. As a result of this inter-service competition and a reluctance to commit the necessary monies, the Pentagon put off making any decision.
In November of 1972, Col. Bradford Parkinson was the director of engineering for the Advanced Ballistic ReEntry Systems Program (ABRES) at SAMSO. Brig. Gen. Bill Dunn, who led the advance planning group (XR), identified Parkinson as a potential candidate to head the floundering 621B program. At Dunn’s behest, Lt. Gen. Kenneth Schultz, commander of SAMSO, asked Parkinson if he would like to be assigned to the 621B program. Parkinson had a very relevant background in navigation, guidance, and control that included a Ph.D. from Stanford in astronautical engineering. He had been chair of the Astronautics Department at the U.S. Air Force Academy, spent three years as a guidance analyst at the Central Inertial Guidance Test Facility, and was operationally oriented with 26 combat missions in AC-130 gunships.
The background was a match, but Parkinson expressed an unwillingness to volunteer for the assignment if he were not assured that he would be the program director. Schultz said he could not yet make that promise. However, immediately after Parkinson left his office, the general reassigned him to the 621B program and effectively made him the director.
Beginning in December, immediately after he assumed control of 621B, Parkinson instituted a series of 7 a.m. educational meetings. At these gatherings, the program staff reexamined every aspect of the proposed 621B program, including alternatives. This educational process was a key to having everyone in the Program Office completely understand the technical issues they faced.
During this period Gen. Schultz supported the program in every way that he could. In particular, Parkinson was allowed to recruit Air Force officers whose background and experience were aligned with the needs of the fledgling program. All had advanced engineering degrees from the very best universities in the country including MIT, Michigan, and Stanford. In addition, virtually every officer had experience in developing real hardware or in testing inertial guidance systems. The first officer Parkinson brought aboard was Air Force Major Gaylord Green, who had worked for him on ABRES. Green’s creativity, focused on satellites and orbits, had an extremely important impact on the success of GPS.
The result of Parkinson’s hunting license was a cadre of about 25 of the best and brightest people that the Air Force had to offer.
In addition there was a small, carefully-selected group of Aerospace technical support personnel (led by Walt Melton from 1970 to 1972). This fine group of Aerospace engineers and scientists was experienced in an all technical aspects of space navigation programs and particularly skilled at issues relating to signal modulation, satellite position prediction, and building long-life satellites. Many of their names will be highlighted in Part Two of this story. The Aerospace contingent continued to enjoy the strong support of the president of the Aerospace Corporation, Ivan Getting.
Replacing Melton early in Phase One was Ed Lassiter, who had extensive space-flight experience and was a mainstay of the early GPS development.
Credit: Bradford W. Parkinson and Stephen T. Powers
During early spring of 1973, the director of Defense Research and Engineering (DDR&E), Dr. Malcolm Currie, formerly of Hughes Aircraft, who had just been appointed to the number three position in the DoD, found himself flying between Washington, D.C. and Los Angeles on most weekends. His secondary purpose was to oversee the relocation of his family, but he needed an official reason to travel to Los Angeles. So, each Friday afternoon he would visit SAMSO in Los Angeles for a presentation. After a few weeks, his host Gen. Schultz ran out of subjects to present, and instead invited Currie to spend an afternoon with his new program director, Col. Parkinson.
Schultz’s invitation led to an astonishing meeting, because a newly-promoted colonel does not usually have the opportunity to confer with the number three person in the DoD over an uninterrupted three- or four-hour period. This informal meeting was held in private, in a very small cubicle within the JPO offices. With a Ph.D. in physics, Currie was a very quick study, so the interaction was lively and deep, delving into every aspect of the 621B proposal. After that meeting, Currie became a good friend to and a sponsor of the new satellite-based navigation program. He later played a critical role in ensuring DoD support, particularly in light of the Air Force’s attempts to cancel the infant program.
DSARC 1. On August 17, 1973, Parkinson was invited to the Defense Systems Acquisition Review Council meeting to make a presentation on 621B. The meeting’s purpose was to determine whether to proceed with the concept demonstration program. It was held at the Pentagon, and attended by senior officers of all services, with Mal Currie presiding. At the meeting’s conclusion, the Council voted against approving the 621B program. Currie immediately invited Parkinson into his private office to tell him he wanted a new system proposal developed that would incorporate the best features of all the technical alternatives. He emphasized the need for a joint program involving all services.
Lonely Halls Meeting. Parkinson immediately called a meeting in the Pentagon over Labor Day weekend, September 1973. Over that weekend, the world’s largest office building appeared to be a series of poorly-lit, uninhabited tunnels because everyone was away on vacation. The light at end of those tunnels, both figuratively and literally, came from a small conference room on the top floor, seating about a dozen attendees, all Air Force officers except for three Aerospace Corporation engineers. The purpose of the meeting was to define modifications to the 621B proposal that would meet Currie’s directive. Parkinson wanted the isolation to ensure unfettered creativity in defining the new proposal.
Leading to this, the Analytical Sciences Corporation (TASC) under the guidance of Gaylord Green had completed a new systems study, a review and update of the earlier systems study directed by Jim Woodford and Hideyoshi Nakamura for project 621B in 1964–66.
After much deliberation, over that weekend the JPO defined the GPS with ten facets:
The fundamental 621B concept of simultaneous passive ranging to four satellites would be the underlying principle of the new system proposal, ensuring that user equipment would not require a synchronized atomic clock.
The signal structure would be the 621B CDMA modulation. It would include both a clear, acquisition modulation (C/A) and a precision military modulation (P/Y). The C/A modulation was to be freely available to civil users throughout the world.
There would be two GPS broadcast frequencies in the L band, using the same dual-frequency technique that Transit had employed to correct for ionospheric group delay, as well as providing redundancy.
Based on the progress that NRL had made in satellite clocks, the program committed to space-hardened atomic clocks on the first operational/demonstration GPS satellites (called Navigation Development Satellites, or NDS). At the Lonely Halls meeting, Parkinson concluded that the NRL technology was relatively low-risk, obviating the need to use the ground-relay, experimental demonstration scheme that 621B had previously proposed. It later turned out that the clock development was not as mature as it appeared, but the JPO backup clock development by Rockwell was available in time for the first launch.
The orbits for the satellites were to be inclined at 62º and not geosynchronous. Green proposed 11-hour, 58-minute (sidereal synchronous) orbits that gave about two hours of testing over the same United States test area each day. NRL had advocated similar 8- or 12-hour inclined orbits. Because of the need for an extensive testing program on an instrumented range, exact 8- or 12-hour orbits would have been unsatisfactory, because they would continuously shift relative to the Earth. While these orbits resembled those advocated by NRL, Green’s modification was critical to the success of the testing program.
Orbit prediction would be handled with modifications to the Transit-developed orbit-prediction programs called Celeste.
The initial test constellation would include four operational satellites, competitively procured, one of which would be a refurbished qualification model. They would be launched on refurbished Atlas-F rockets, which minimized cost, but also limited the number of solar panels that could be carried because of weight.
A family of user equipment prototypes would be procured competitively. This equipment would span all normal military uses, and also include a low-cost set that would prototype civilian use. Where affordable, competitive contracts would be let. Particular attention would be devoted to user equipment integration with inertial navigation units and demonstration of anti-jam capabilities.
The master control station and its backup would be on U.S. soil, but monitor stations would be placed around the world. >
The testing would be principally performed at the Army’s Yuma test range with accuracy measured from a tri-lateration laser configuration. Using three laser ranging devices at the same time would ensure that all test vehicles could be measured to about a meter of positioning error. It was expected (and later proven) that this technique could even calibrate Air Force or Navy fighter aircraft flying close to Mach 1. Testing would make use of the inverted range concept, with satellites replacing each range transmitter as each newly launched GPS satellite became operational on orbit.
Dual Use. One aspect should be strongly pointed out. Contrary to some versions of GPS history, from the very beginning, GPS was configured to be a dual-use system. Civilian users were to be given free access to the signal specification and were expected to use the so-called clear acquisition signal for navigation and other purposes. In fact, Parkinson highlighted civilian use when he testified before Congress on the proposed new system.
GPS Approval. That Labor Day weekend of September 1973 had been a very busy three days. With help from the Air Staff Program Element Monitor (PEM) Lt. Col. Paul Martin, the Lonely Halls gathering developed a seven-page Decision Coordinating Paper (DCP) and a presentation of the new concept. Over the next two-and-a-half months there was a flurry of activity as Parkinson made presentations and defended the concept before all those who could block the proposal in the Pentagon. This effort was culminated with the approval to proceed on December 14, 1973. There were no significant modifications to the proposal that had been developed during the Lonely Halls meeting in the Pentagon.
During the whole Phase I development, Parkinson resolved to avoid any conflict with the other original competitors to build a satellite-based navigation system. He deliberately ignored dubious claims of invention and statements regarding the origins of GPS technology. Until quite recently, he has overlooked these false claims by those who did not directly participate in determining the GPS architecture and did not participate in the specific GPS design and deployment. He felt the real purpose was to build the system, not to fight over credit.
Recently an article appeared that implied that the GPS design was essentially the same as Timation. (“In what ways did GPS improve on Timation?” Easton: “I can’t think of any ways in which GPS improved on Timation. Essentially, they are the same system.” Interview in High Frontier magazine.)
Aware that this incorrect statement denigrated the people who had first analyzed, advocated, and demonstrated the fundamental concept, as well as built the system, Parkinson resolved to correct the record, and highlight the names of those who deserve credit. This is a major purpose of this article. This article has been reviewed and approved for veracity by virtually all the key figures (still alive) who actually designed, built, and tested GPS.
End of Part One. Watch for Part Two in our June issue.
Some of the JPO Heroes at a Dining In. From left, Major Mel Birnbaum (made many important contributions. He was famous for marathon code reviews that could last 18 hours straight. He hated to miss schedules!); Col. Don Henderson (later Maj. Gen.), second Air Force Deputy; Major Ralph Tourino (later Maj. Gen.), Program Control; Lt. Col. Ken Juvette, director of procurement; and Lt. Cdr. Joe Strada, a key leader in the extensive test program. (Credit: Bradford W. Parkinson and Stephen T. Powers)
Our Story Continues
Part 2 of “The Origins of GPS” appears in the June 2010 issue of GPS World. GPS Phase I program approval meant that the real work could begin. By January 1974, the GPS program at the JPO was well underway. Of course there were many challenges, but Five Challenges, principally engineering, stand out as particularly daunting. Part Two also describes GPS’ most fundamental innovation, more on system origins, innovations of the Joint Program Office (see photo of key figures), and thoughts on the future of GPS and GNSS.
item: Cell phone jammer kit , how to make a simple cell phone jammer
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cell phone jammer kit
Apple design m2763 ac adapter 12vdc 750ma -(+) 2.5x5.5mm used 12,deer computer ad1605cw ac adapter 5.5vdc 2.3a power supply,viewsonic adp-80ab ac adapter 12vdc 6.67a 3.3x6.4mm -(+)- power.ault t48-161250-a020c ac adapter 16va 1250ma used 4pin connector,complete infrastructures (gsm,acbel ada017 ac adapter 12vdc 3.33a used -(+) 2.5x6.2x9mm round.ilan f1560 (n) ac adapter 12vdc 2.83a -(+) 2x5.5mm 34w i.t.e pow,canon ad-50 ac adapter -(+)- +24vdc 1.8a used 2x5.5mm straight r,additionally any rf output failure is indicated with sound alarm and led display.liteon pa-1151-08 ac adapter 19v 7.9a used 3.3 x 5.5 x 12.9mm,where shall the system be used,jutai jt-24v250 ac adapter 24vac 0.25a 250ma 2pin power supply,ttx23073001 ac adapter 5v 1a wallmount charger i.t.e power suppl.casio computers ad-c52s ac adapter 5.3vdc 650ma used -(+) 1.5x4x,65w-dlj104 ac adapter 19.5v dc 3.34a dell laptop power supply,delta eadp-45bb b ac adapter 56vdc 0.8a used -(+) 2.5x5.5x10.4mm,2100 to 2200 mhzoutput power,moso xkd-c2000ic5.0-12w ac adapter 5vdc 2a used -(+) 0.7x2.5x9mm,bomb threats or when military action is underway,targus pa104u ac power inverter used auto air charger dell 12vdc,religious establishments like churches and mosques,dve dsc-5p-01 us 50100 ac adapter 5vdc 1a used usb connector wal.altec lansing s012bu0500250 ac adapter 5vdc 2500ma -(+) 2x5.5mm.canon cb-2lv g battery charger 4.2vdc 0.65a used ite power suppl.cell phone jammer is an electronic device that blocks transmission of …,this causes enough interference with the communication between mobile phones and communicating towers to render the phones unusable.hp f1044b ac adapter 12vdc 3.3a adp-40cb power supply hp omnibo,dvacs dv-1250 ac adapter 12vdc 0.5a used 2 x 5.4 x 11.9mm.phihong psm11r-090 ac adapter 9vdc 1.12a -(+)- 2.5x5.5mm barrel,the electrical substations may have some faults which may damage the power system equipment,shanghai dy121-120010100 ac adapter 12v dc 1a used -(+) cut wire,yj yj-502
ac adapter 13.5v dc 1.3a used mini usb connector p,868 – 870 mhz each per devicedimensions.what is a cell phone signal jammer,hp hstnn-ha01 ac adapter 19vdc 7.1a 135w used 5x7.4mm.starting with induction motors is a very difficult task as they require more current and torque initially,liteon pa-1121-02 ac adapter 19vdc 6.3a 2mm -(+)- hp switching p,foxlink fa-4f020 ac adapter 6vdc 1a used -(+) 1.5x4x8.4mm 90° ro,deer ad1605cf ac adapter 4-5.5v 2.6 2.3a used -(+) 2.5x5.5mm rou.sanyo ad-177 ac adapter 12vdc 200ma used +(-) 2x5.5mm 90° round.condor dsa-0151d-12 ac adapter 12v dc 1.5a switching power suppl.honor ads-7.fn-06 05008gpcu ac adapter 5v 1.5a switching power.sharp ea-51a ac adapter 6vdc 200ma usedstraight round barrel p.delta adp-36jh b ac adapter 12vdc 3a used -(+)- 2.7x5.4x9.5mm.dell lite on la65ns2-01 ac adapter 19.5vdc 3.34a used -(+) pin,aps aps40-es-30 ac adapter +5v 6a +12v 1a -12v 0.5a used 5pin,delta adp-65jh db ac adapter 19v 3.42a acer travelmate laptop po,bothhand m1-8s05 ac adapter +5v 1.6a used 1.9 x 5.5 x 9.4mm,they operate by blocking the transmission of a signal from the satellite to the cell phone tower,universal 70w-a ac adapter 12vdc used 2.4 x 5.4 x 12.6mm detacha,panasonic pqlv219 ac adapter 6.5vdc 500ma -(+) 1.7x4.7mm power s,powerup g54-41244 universal notebook ac adapter 90w 20v 24v 4.5a,sos or searching for service and all phones within the effective radius are silenced.
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It consists of an rf transmitter and receiver,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,replacement vsk-0725 ac adapter 7.9vdc 1.4a power supply for pan.overload protection of transformer,mka-35090300 ac adapter 9vac 300ma used 2x5.5mm ~(~) 120vac 2.1,nextar fj-t22-1202500v ac adapter 12v 250ma switching power supp,dell adp-220ab b ac adapter 12v 18a switching power supply.ibm pa-1121-071 ac adapter 16vdc 7.5a used 4-pin female 02k7086.ottoman st-c-075-19000395ct ac adapter 19vdc 3.95a used3 x 5.4.motorola psm4250a ac adapter 4.4vdc 1.5a used cellphone charger,ibm 35g4796 thinkpad ac dc adapter 20v dc 700 series laptop pow.in this blog post i'm going to use kali linux for making wifi jammer,khu045030d-2 ac adapter 4.5vdc 300ma used shaver power supply 12,motorola ssw-2285us ac adapter 5vdc 500ma cellphone travel charg.good grounding rules are followed in the design,there are many types of interference signal frequencies,toshiba pa2400u ac adapter 18v 1.1a notebook laptop power supply,hp ac adapter c6320-61605 6v 2a photosmart digital camera 315,ryobi p113 ac adapter 18vdc used lithium ion battery charger p10,neosonic power express charger ac adapter 24v dc 800ma used,motorola 481609oo3nt ac adapter 16vdc 900ma used 2.4x5.3x9.7mm,braun 4729 ac adapter 250vac ~ 2.5a 2w class 2 power supply,panasonic pqlv208 ac adapter 9vdc 350ma -(+)- used 1.7 x 4.7 x 9.creative ys-1015-e12 12v 1.25a switching power supply ac adapter,over time many companies originally contracted to design mobile jammer for government switched over to sell these devices to private entities.hipower a0105-225 ac adapter 16vdc 3.8a used -(+)- 1 x 4.5 x 6 x.apple powerbook m1893 ac adapter 16vdc 1.5a 16v 1a used 4 pin di,this system also records the message if the user wants to leave any message.to create a quiet zone around you.bi zda050050us ac adapter 5v 500ma switching power supply.when the temperature rises more than a threshold value this system automatically switches on the fan,the latest 5g signal jammers are available in the jammer -buy store,dish networkault p57241000k030g ac adapter 24vdc 1a -(+) 1x3.5mm.matsushita etyhp127mm ac adapter 12vdc 1.65a 4pin switching powe.fld0710-5.0v2.00a ac adapter 5vdc 2a used -(+) 1.3x3.5mm ite pow.we have designed a system having no match,motorola ch610d walkie talkie charger only no adapter included u.this article shows the circuits for converting small voltage to higher voltage that is 6v dc to 12v but with a lower current rating,sun fone actm-02 ac adapter 5vdc 2.5a used -(+)- 2 x 3.4 x 9.6 m,chd ud4120060060g ac adapter 6vdc 600ma 14w power supply.smart charger h02400015-us-1 ac adapter battery pack charger,armaco ba2424 ac adapter 24vdc 200ma used 117v 60hz 10w power su.edac ea10523c-120 ac adapter 12vdc 5a used 2.5 x 5.5 x 11mm.compaq evp100 ac dc adapter 10v 1.5a 164153-001 164410-001 4.9mm.new bright a519201194 ac dc adapter 7v 150ma charger,-20°c to +60°cambient humidity.condor hka-09100ec-230 ac adapter 9vdc 1000ma 9va used 2.4x5.5mm,rocketfish rf-mcb90-t ac adapter 5vdc 0.6a used mini usb connect,power rider sf41-0600800du ac adapter 6vdc 800ma used 2 pin mole,we have already published a list of electrical projects which are collected from different sources for the convenience of engineering students,grundig nt473 ac adapter 3.1vdc 0.35a 4vdc 0.60a charging unit l.-10°c – +60°crelative humidity.motorola dch3-050us-0303 ac adapter 5vdc 550ma used usb mini ite.
Sanyo scp-01adtac adapter 5.5v 950ma travel charger for sanyo,phihong psa31u-050 ac adapter 5vdc 4a 1.3x3.5mm -(+) used 100-24,considered a leading expert in the speed counter measurement industry.hp hstnn-la01-e ac adapter 19.5vdc 6.9a 135w used -(+) 0.6x5x7.5,changzhou un-d7.2v200 ac dc adapter 7.2vdc 200ma -(+) used 120va,this paper uses 8 stages cockcroft –walton multiplier for generating high voltage,a mobile phone jammer is an instrument used to prevent cellular phones from receiving signals from base stations,umec up0451e-15p ac adapter 15vdc 3a 45w like new -(+)- 2x5.5mm,ibm 85g6704 ac adapter 16v dc 2.2a power supply 4pin 85g6705 for,dynex dx-nb1ta1 international travel adapter new open pack porta,motorola psm5185a cell phone charger 5vdc 550ma mini usb ac adap,viii types of mobile jammerthere are two types of cell phone jammers currently available,recoton adf1600 voltage converter 1600w 500watts.even temperature and humidity play a role,hipro hp-a0652r3b ac adapter 19v 3.42a used 1.5x5.5mm 90°round b,intelink ilp50-1202000b ac adapter 12vdc 2a used -(+)- 2.3 x 5.3,finecom py-398 ac dc adapter 12v dc 1000ma2.5 x 5.5 x 11.6mm.cisco adp-30rb ac adapter 5v 3a 12vdc 2a 12v 0.2a 6pin molex 91-,finecom ky-05036s-12 ac adpter 12vdc 5v dc 2a 5pin 9mm mini din,goldfear ac adapter 6v 500ma cellphone power supply,trendnet tpe-111gi(a) used wifi poe e167928 100-240vac 0.3a 50/6.group west 3a-251dn12 ac adapter 12vdc 2a -(+) used2.5x5.5mm r,shun shing dc12500f ac adapter 12vdc 500ma used -(+) 2x5.5x8mm r.finecom gt-21089-1305-t2 ac adapter 5v 2.6a new 3pin din power.ibm 73p4502 ac adapter 16vdc 0 - 4.55a 72w laptop power supply.condor a9-1a ac adapter 9vac 1a 2.5x5.5mm ~(~) 1000ma 18w power,variable power supply circuits,cool-lux ad-1280 ac adapter 12vdc 800ma battery charger.ibm 08k8204 ac adapter 16vdc 4.5a -(+) 2.5x5.5mm 100-240vac used,vi simple circuit diagramvii working of mobile jammercell phone jammer work in a similar way to radio jammers by sending out the same radio frequencies that cell phone operates on,chuan ch35-4v8 ac adapter 4.8v dc 250ma used 2pin molex power,st-c-075-18500350ct replacement ac adapter 18.5v dc 3.5a laptop,our grocery app lets you view our weekly specials,proton spn-445a ac adapter 19vdc 2.3a used 2x5.5x12.8mm 90 degr,sony ac-l10a ac adapter 8.4vdc 1.5a used flat 2pin camera charge,rova dsc-6pfa-12 fus 090060 ac adapter +9vdc 0.6a used power sup,ktec ka12a120120046u ac adapter 12vac 1200ma ~(~)~ 2x5.5mm linea,toshiba adp-75sb ab ac dc adapter 19v 3.95a power supply,polycomfsp019-1ad205a ac adapter 19v 1a used -(+) 3 x 5.5mm 24.hp compaq ppp009l ac adapter 18.5vdc 3.5a used -(+) with pin ins,hr-091206 ac adapter 12vdc 6a -(+) used 2.4 x 5.4 x 12mm straigh,finecom ac dc adapter 15v 5a 6.3mmpower supply toshiba tec m3,nerve block can have a beneficial wound-healing effect in this regard,canon cb-5l battery charger 18.4vdc 1.2a ds8101 for camecorder c,jobmate ad35-04503 ac adapter 4.5vdc 300ma new 2.5x5.3x9.7mm,royal d10-03a ac adapter 10vdc 300ma used 2.2 x 5.3 x 11 mm stra,the new system features a longer wear time on the sensor (10 days).a leader in high-precision gnss positioning solutions,toshiba pa3673e-1ac3 ac adapter 19v dc 12.2a 4 pin power supply,rim psm05r-068r dc adapter 6.8v dc 0.5a wall charger ite,delta adp-50gb ac dc adapter 19v 2.64a power supply gateway,3500g size：385 x 135 x 50mm warranty：one year,sector 5814207 ac adapter +5vdc 2a 5.4va used -(+) 1.5x2.5x9.8mm.
Ac power control using mosfet / igbt.hp pa-1650-02hp ac adapter 18.5v 3.5a 65w used 1.5x4.8mm,-20°c to +60°cambient humidity,d-link am-0751000d41 ac adapter 7.5vdc 1a used -(+) 2x5.5mm 90°,positec machinery sh-dc0240400 ac adapter 24vdc 400ma used -(.sony ac-v65a ac power adapter 7.5vdc 10v 1.6a 1.3a 20w charger p.aironet ad1280-7-544 ac adapter 12vdc 800ma power supply for med,the company specializes in counter-ied electronic warfare,transmission of data using power line carrier communication system.gamestop 5v wii remote conteroller charging dock.this combined system is the right choice to protect such locations,zyxel a48091000 ac adapter 9v 1000ma used 3pin female class 2 tr.disrupting the communication between the phone and the cell-phone base station,panasonic cf-aa1526 m3 ac adapter 15.1vdc 2.6a used pscv390101.the first circuit shows a variable power supply of range 1,sony pcga-ac19v1 ac adapter 19.5 3a used -(+) 4.4x6.5mm 90° 100-.d-link m1-10s05 ac adapter 5vdc 2a -(+) 2x5.5mm 90° 120vac new i,lenovo 42t4430 ac adapter 20v 4.5a 90w pa-190053i used 5.6 x 7.9,delta eadp-30hb b +12v dc 2.5a -(+)- 2.5x5.5mm used ite power.ktec ka12d090120046u ac adapter 9vdc 1200ma used 2 x 5.4 x 14.2,replacement 75w-hp21 ac adapter 19vdc 3.95a -(+) 2.5x5.5mm 100-2.zhongshan p1203e ac adapter 12vdc 2a used -(+) 2x5.5x9mm round b,aci communications lh-1250-500 ac adapter -(+) 12.5vdc 500ma use.chd dpx411409 ac adapter 4.5vdc 600ma class 2 transformer,sanyo scp-06adt ac adapter 5.4v dc 600ma used phone connector po,the signal must be < – 80 db in the locationdimensions,yuyao wj-y666-12 ac adapter 12vdc 500ma used -(+) 2.1x5.5x12mm r,1800 to 1950 mhz on dcs/phs bands,ault mw153kb1203f01 ac adapter 12vdc 3.4a -(+) used 2.5x5.5 100-,produits de bombe jammer+433 -+868rc 315 mhz,it's compatible with all major carriers to boost 4g lte and 3g signals,mobile jammers effect can vary widely based on factors such as proximity to towers,motorola fmp5334a ac dc adapter used 5vdc 550ma usb connector wa,delta adp-5vb c ac adapter 5vdc 1a power supply n4000e.ii mobile jammermobile jammer is used to prevent mobile phones from receiving or transmitting signals with the base station.radioshack 273-1695 ac adapter 3,5,6,6.5vdc 2.5a digital camera,energizer pl-7526 ac adapter6v dc 1a new -(+) 1.5x3.7x7.5mm 90.dsa-0051-03 ac dc adapter 5v 1000ma power supply,li shin lse9802a1240 ac adapter 12v 3.3a 40w power supply 4 pin,lionville 7567 ac adapter 12vdc 500ma used -(+) 2x5.5mm 120vac 2,thinkpad 40y7649 ac adapter 20vdc 4.55a used -(+)- 5.5x7.9mm rou,wtd-065180b0-k replacement ac adapter 18.5v dc 3.5a laptop power,durabrand rgd48120120 ac adapter 12vdc 1.2a -(+) 2x5.5mm 1200ma,delta adp-62ab ac adapter 3.5vdc 8a 12.2v 3a used 7pin 13mm din,hp hp-ok65b13 ac adapter 18.5vdc 3.5a used -(+) 1.5x4.7x11mm rou.mayday tech ppp014s replacement ac adapter 18.5v dc 4.9a used,delta adp-65jh db ac adapter 19vdc 3.42a used 1.5x5.5mm 90°rou.sony ac-ls5b ac dc adapter 4.2v 1.5a cybershot digital camera.digipos retail blade psu2000 power supply 24vdc 8.33a ac adapter.hoyoa bhy481351000u ac adapter 13.5vdc 1000ma used -(+) 2.5x5.5x,we then need information about the existing infrastructure,the frequencies are mostly in the uhf range of 433 mhz or 20 – 41 mhz.temperature controlled system.
Ibm 02k6794 ac adapter -(+) 2.5x5.5mm16vdc 4.5a 100-240vac power,the aim of this project is to develop a circuit that can generate high voltage using a marx generator.motorola psm4562a ac adapter 5.9v dc 400ma used,eos zvc70ns18.5w ac adapter 18v 3.6a laptop ti travelmate 7000 7,the control unit of the vehicle is connected to the pki 6670 via a diagnostic link using an adapter (included in the scope of supply),texas instruments 2580940-6 ac adapter 5.2vdc 4a 6vdc 300ma 1,phihong psa31u-120 ac adapter 12vdc 2.5a -(+) 2x5.5mm used barre,sanyo 51a-2824 ac travel adapter 9vdc 100ma used 2 x 5.5 x 10mm.lenovo 92p1160 ac adapter 20vdc 3.25a new power supply 65w.the output of that circuit will work as a jammer.and 41-6-500r ac adapter 6vdc 500ma used -(+) 2x5.5x9.4mm round.lenovo 42t4434 ac adapter 20vdc 4.5a new -(+) 5.1x8x11.3mm.motorola fmp5358a ac adapter 5v 850ma power supply,mobile jammers block mobile phone use by sending out radio waves along the same frequencies that mobile phone use.samsung ad-6019a ac adapter 19vdc 3.15a laptop power supply,the if section comprises a noise circuit which extracts noise from the environment by the use of microphone,samsung atadu10ube ac travel adapter 5vdc 0.7a used power supply,the rating of electrical appliances determines the power utilized by them to work properly.ault 3com pw130 ac adapter 48vdc 420ma switching power supply,here is the project showing radar that can detect the range of an object.toshiba pa3237u-1aca ac adapter 15v dc 8a used 4pin female ite,now we are providing the list of the top electrical mini project ideas on this page,three phase fault analysis with auto reset for temporary fault and trip for permanent fault,wifi jammer is very special in this area,eng 3a-154wp05 ac adapter 5vdc 2.6a -(+) used 2 x 5.4 x 9.5mm st.this project shows the measuring of solar energy using pic microcontroller and sensors,you can clearly observe the data by displaying the screen,gpe gpe-828c ac adapter 5vdc 1000ma used -(+) 2.5x5.5x9.4mm 90°.tec rb-c2001 battery charger 8.4v dc 0.9a used b-sp2d-chg ac 100,dv-751a5 ac dc adapter 7.5vdc 1.5a used -(+) 2x5.5x9mm round bar.logitech l-ld4 kwt08a00jn0661 ac adapter 8vdc 500ma used 0.9x3.4,s15af125120 ac adapter 12.5vdc 1200ma used -(+) 2x5.5x11mm rou.auto charger 12vdc to 5v 0.5a car cigarette lighter mini usb pow.d-link van90c-480b ac adapter 48vdc 1.45a -(+) 2x5.5mm 100-240va,oem ad-0760dt ac adapter 7.vdc 600ma new -(+)- 2.1x5.4x10mm.accordingly the lights are switched on and off.radioshack 43-3825 ac adapter 9vdc 300ma used -(+) 2x5.5x11.9mm,sony ac-12v1 ac dc adapter 12v 2a laptop power supply,outputs obtained are speed and electromagnetic torque,campower cp2200 ac adapter 12v ac 750ma power supply,cincon electronics tr36a15-oxf01 ac adapter 15v dc 1.3a power su,hon-kwang hk-u-120a015-us ac adapter 12vdc 0-0.5a used -(+)- 2x5.here is the circuit showing a smoke detector alarm,htc psaio5r-050q ac adapter 5v dc 1a switching usb power supply.bionx sa190b-24u ac adapter 26vdc 3.45a -(+)- 89.7w charger ite.vtech s004lu0750040(1)ac adapter 7.5vdc 3w -(+) 2.5x5.5mm round.raheem is described to be around 6-2 with a slim build,d-link ad-0950 ac adapter 9vdc 500ma used -(+) 2x5.5x11mm 90° ro,information technology s008cm0500100 ac adapter 5vdc 1000ma used.li tone electronics lte24e-s2-1 12vdc 2a 24w used -(+) 2.1x5.5mm.potrans up01011050 ac adapter 5v 2a 450006-1 ite power supply.a spatial diversity setting would be preferred,this project shows charging a battery wirelessly.
Eng 3a-161da12 ac adapter 12vdc 1.26a used 2x5.5mm -(+)- 100-240,compaq 340754-001 ac adapter 10vdc 2.5a used - ---c--- + 305 306,atlinks usa inc. 5-2509 ac dc adapter 9v 450ma 8w class 2 power,gnt ksa-1416u ac adapter 14vdc 1600ma used -(+) 2x5.5x10mm round,motorola fmp5202a travel charger 5v 850ma for motorola a780.motorola 5864200w13 ac adapter 6vdc 600ma 7w power supply,liteon pa-1650-02 ac adapter 19v dc 3.42a used 2x5.5x9.7mm,utstarcom psc11a-050 ac adapter +5vdc 2a used -(+) 1.5x4mm cru66,radioshack 15-1838 ac adapter dc 12v 100ma wallmount direct plug,baknor bk 3500-b3345pip ac adapter 3vdc 500ma used 1x2.2x9.7mm.bti veg90a-190a universal ac adapter 15-20v 5.33a 90w laptop pow,artesyn ssl12-7630 ac adapter 12vdc 1.25a -(+) 2x5.5mm used 91-5.esaw 450-31 ac adapter 3,4.5,6,7.5,9-12vdc 300ma used switching.dve dsa-0151a-12 s ac adapter 12vdc 1.25a used 2.1 x 5.4 x 9.4 m,intermec ea10722 ac adapter 15-24v 4.3a -(+) 2.5x5.5mm 75w i.t.e,dve dsa-0251-05 ac adapter 5vdc 5a used 2.5x5.5x9mm 90 degree.the scope of this paper is to implement data communication using existing power lines in the vicinity with the help of x10 modules.cbm 31ad ac adapter 24vdc 1.9a used 3 pin din connector,asian power devices inc da-48h12 ac dc adapter 12v 4a power supp,breville ecs600xl battery charger 15vdc 250ma 12volts used.creative tesa1-050240 ac dcadapter 5v 2.4a power supply,the single frequency ranges can be deactivated separately in order to allow required communication or to restrain unused frequencies from being covered without purpose.apd wa-18g12u ac adapter 12vdc 1.5a -(+)- 2.5x5.5mm 100-240vac u..
