This section expands on common questions and dives into a bit more detail on certain aspects of the history and development of the Low Frequency Range, as well as other related radio navigation systems.
By “system” we are referring to an organized, purpose-built network of multiple radio aids for aerial navigation. If we consider systems that were widely adopted and available to any aircraft that wanted to use them, the Low Frequency Radio Range would be the first such system in history. If we consider systems that guided aircraft along specific airways, e.g., “highways in the sky”, LFR is definitely the first system. However, in terms of the first workable radio navigation system there was another that preceded it by 16 years.
Germany’s Telefunken Kompass Sender (“Compass Transmitting Station” and the origin of the term "Radio Compass") came into service around 1912 and used a large 120-meter diameter array of 32 dipole antennae arranged like a compass dial. After an initial omnidirectional timing signal, each antenna would energize in sequence and send a bi-directional beam that swept around the full circle in 30 seconds. It was, in principle, a very slow-motion version of a VOR, where the user (synching a specialized stopwatch) would listen to the relative volume of each pulse. At the “null,” where the signal was weakest, the user knew a specific dipole was pointed at them and could determine their bearing within about 5°. Two stations were built at Kleve and Tønder (now in Denmark) to provide a more accurate fix. It was a technical achievement; however, given the size and fragility of the primitive radios of the time, military Zeppelins were the primary users: push button “radiotelegraphs” were just experimentally making it into the noisy, open cockpits of airplanes so it never saw widespread use there. Over 30 stations were planned, but the First World War intervened and service ended by 1918 with no other stations built.
Beyond that, the first radio navigation aid were indeed “Homing” beacons, now called Non-Directional Beacons (NDB’s); basically, any radio transmitter can be used for this purpose by a radio compass. Ships began to experiment with them in 1903, Zeppelins also used them and the US Navy conducted the first successful airborne test in 1920. However, throughout the 1920’s the stations tended to be ad-hoc experiments or ordinary commercial stations and not a specific system per se and, as covered earlier, the technology would remain heavy, complex, expensive and rudimentary until World War II. The US would go on to set up many NDB’s after the rollout of LFR in 1928 (typically at Army Air Force bases for their larger aircraft) and in reviewing the sectionals they were clearly always secondary to the range stations that outnumbered them). Contrary to a few sources, when the first radio airways were set up in the US, it was beams of the LFR and not the NDB’s that defined them.
LFR and other systems that would follow were (a) specifically developed as large-scale programs with numerous sites, (b) were widely adopted by civilian and military aviation and (c) utilized for decades. All were used internationally. Here are the dates they were developed and implemented:
By this account, it appears that LFR had a six-year head start ahead of the Lorenz Beam which took off in the 30’s and over a decade on the other systems that would propagate in the 1940’s. Of these only Lorenz, VAR and VOR also provided immediate “real time” guidance along a specific airway or course with minimal work for the pilot. The rest only established a bearing or fix at one point in time, which the pilot would then need to analyze further to determine any necessary course correction.
LFR also already had at least 7 operational stations in the US by the time England's Orfordness Beacon went on-air July 1929. It used a similar concept to the Telefunken system described above, as well as an experimental 1920 maritime beacon developed by Marconi, where a rotating loop antenna was used instead of a fixed array to smoothly sweep the directional signal after the omnidirectional timing pulse. Only one sister station was built at Farnborough before it was surpassed by other efforts.
The basic principles of VAR and VOR, the successors to LFR, are covered on the Its Fate Page. A quick overview of the other systems is as follows:
Germany’s Lorenz Beam (named after the company) was, in essence, a narrow single aural “beam” that used two slightly overlapping 33.33Mhz signals, one of dots and the other of dashes, that merged to create an on-course "equisignal" tone. The two signals were actually a single signal transmitted on a center dipole antenna. A cam switch activated two adjacent dipole reflectors on either side that would rapidly deflect the signal pattern back and forth across the centerline to form the dot and dash lobes. It was used successfully by the 1930’s as an early Instrument Landing System and for long range navigation (Australia preferred this system over LFR). During the “Battle of the Beams” the “Knickebein” bombing aid intersected two powerful versions of such beams over targets in England. The rise of the VOR, VAR and modern Instrument Landing Systems would all make the Lorenz Beam obsolete by 1960.
The Elektra-Sonnen system (simply “Sonne,” German for “sun") was implemented by Germany at the start of World War II in occupied Europe and neutral Spain. The British also surreptitiously used it and named it Consol (Latin for “by the sun”). It combined the Lorenz Beam and Orfordness concepts by radiating 18 rotating equisignals that, after the omnidirectional timing pulse and station ID was sent, would each then sweep across a fixed pie-shaped sector roughly 15° wide over a 30 second period. These sectors were plotted on charts and arranged in two equal opposed “fans” about 135° wide on each side of the station. They were formed by a continuous 250-350khz signal from a center antenna, flanked by two more spaced 3 wavelengths away (about 1.8 miles). The signal alternated between these outer antennae at 1-second intervals to create two heart-shaped “cardioid” dot and dash patterns. Additionally, their signal phase was adjusted to create deep “ripples” (e.g. lobes formed by wave interference) that counterrotated around the edges of both patterns. These interacted to form the many moving equisignals. Technically, these were condensed hyperbolic waveforms between the 3 antennae but from miles away these patterns appeared to radiate from a single point like the rays of the Sun, hence the system’s name.
After using a radio compass, last known position or other means to determine the sector the aircraft was likely in, the number of dots heard after the timing pulse would be counted until the equisignal emerged which then faded into dashes. A chart or table would convert this count into a bearing accurate to within ½° to ¼°. It took a few minutes to assess the 2 to 3 counts needed to most accurately derive a bearing, but like LFR only a simple AM receiver was needed. Its simplicity (e.g. just count the dots) and 1,000-mile range kept it in service in for 50 years, the last station going off-air in 1991.
Hyperbolic Navigation also emerged during the war. It used the time between an initial signal pulse sent by a “master” station that was responded to by another pulse from two or more or “slave” stations located hundreds of miles apart along a defined “chain,” after a short time delay, to determine location. Mathematically, a line that has a constant amount of signal delay between two points forms a hyperbola, hence the origin of the term. Dozens of such “lines of position” or LOP’s were plotted on aerial and marine navigation charts for each chain, typically in 100 microsecond (ms) increments. By reading the time difference on a dial or cathode ray tube between the master and at least two slave stations (or a pair of stations on another chain) the user could determine which two lines of position they were on and the intersection marked their location. LOP’s could also be checked against depth soundings, bearings to landmarks or other beacons, etc. to establish location.
The British developed Gee as the first hyperbolic system for its bombing operations which operated at 20-90 Mhz and had a range of a few hundred miles. This inspired the US to shortly follow with LORAN to extend radio navigation for its Atlantic convoys. It operated at a lower frequency of 1.75 to 1.95 Mhz that used skywave propagation to boost its daytime 700-mile range up to 1,400 miles at night. It was fairly easy to use and was accurate to within a few miles. Decca was a similar hyperbolic system (also developed in the US but first implemented in Britain) but used the phase comparison of low frequency waves between 70 and 129Khz to determine distance within a 200-to-400-mile range. In late 1950’s, after “LORAN B” was abandoned during development, “LORAN C” emerged that used both timing and signal phase, like Decca, to provide accuracy to a few hundred yards. It initially used very expensive 100lb receivers; however, the now cheaper, down-market original “LORAN A” receivers became common globally and by the 1970’s microelectronics made LORAN C units small and affordable. Decca further evolved into Omega, a US military only global network of 8 stations that served from 1971 to 1997.
Satellite Navigation would spell the end of hyperbolic navigation. After the successful 1960 deployment of the US Navy Transit satellite system that allowed military users to determine their location from the observed doppler shift of a radio signal from a satellite, the US began to launch the first part of the Global Positioning System in 1978. The accidental 1983 downing of Korean Air Flight 007, which inadvertently strayed into Soviet airspace due to a navigation error, prompted the US to make GPS available to civilian users (initially with a less accurate “selective availability” constraint that was removed in 2000). As compact, cheap and highly accurate GPS receivers became commonplace by the start of the 21st century, hyperbolic navigation systems would be fully decommissioned by 2015, the exception being the Russian CHAYKA and Alpha systems, its parallel versions of LORAN-C and Omega respectively, which are still in use as of 2021. There are now several satellite navigation systems in use; however, as nations realize the vulnerability of satellite constellations to everything from solar flares to unfriendly neighbors, there has been work to create a new “eLORAN” system as a potential terrestrial backup.
Yes, the Ford Motor Company is indeed the official inventor as is made abundantly clear by US Patent #1,937,876 filed in Ford’s name in 1928. The Ford Museum still retains an original 1927 transmitter building and other components in its collection. However, like many inventions in history, there was a long road of others who developed and refined its key concepts and prototypes, and in the end, Ford and the US National Bureau of Standards would have different accounts of its creation.
In 1907, just four years after the Wright Brother’s took flight, German engineer Otto Scheller (who would go on to develop 70+ patents for the Lorenz Company) conceived a radio beacon that used 4 vertical antennae to create two overlapping figure-eight signal patterns. One signal was a dot (the Morse letter “E”) and the other a dash (the Morse “T”) that interlocked to form an on-course signal along 4 beam lines. This was the core principle of the Low Frequency Radio Range. A patent for the system was filed in 1907 with a diagram that resembled a later Adcock range. In 1916 he had the foresight to update the patent to include the recently invented radio goniometer to adjust the beams. A demonstration station was set up in 1917 using the “A” and “N” letters but as with the Kompass Sender above there simply wasn’t yet a fleet of radio equipped planes to take advantage of it. In the economic devastation and severe sanctions that followed Germany’s defeat in the First World War there was little interest in pursuing it further. The idea was simply ahead of its time.
Some sources credit the United States Bureau of Standards for the invention of the LFR, and they certainly had a hand in its development. In 1919 the US Army Air Service established its Engineering Division at McCook Field in Dayton, OH (the Army outgrew it by 1927 and replaced it with Wright Field, now Wright/Patterson Air Force Base). In 1920, the Army further established an “Instrument Section” to develop the fundamental instruments needed for all weather flight. Their research led to the turn and bank indicator and gyrocompass that gave a pilot a sense of “up” and direction in the clouds, but a solution was needed for navigation. That year, they asked the Bureau, the government’s main R&D arm at the time, to develop a suitable radio beacon.
In response, between 1920 and 1923 Bureau scientists Percival Lowell, Francis Dunmore and Francis Engel developed a “directive type” radio beacon that used two compact loop antennae to create a four-course system using the letters “A” and “T”. Sources vary as to the extent that they were aware of Scheller’s design – but vertical antennae were not used and the system lacked a goniometer. The antennae crossed at 45° to accentuate two of the beams along a main course that was assessed. A station was successfully tested in Washington DC by land and sea in May 1921, and in the air by the US Army Air Service and Signal Corps at Dayton in 1923. However, its rudimentary spark gap transmitter required that a plane drag a weighted 200’ antenna behind the aircraft to receive the signals. It was a promising experiment but it was not quite ready for practical commercial use. For reasons unknown, the Bureau’s funding for further development was cut off in 1923.
Although the Bureau was temporarily out of the picture, the US Army Air Service and Signal Corps continued their experiments and were apparently aware of Scheller’s patent. An improved beacon was set up in Dayton by 1924. By 1925 at Monmouth, IL, General Superintendent of the US Airmail Service Carl Egge and Edward Warner of M.I.T. gained permission to set up an “Equi-Signal Radio Beacon.” It was built under supervision of McCook’s Radio Laboratory which was involved in the 1923 test. It used the latest vacuum tube radios, interlocking “A” and “N” signals and first employed a radio goniometer tested by the Signal Corps to adjust the beams – a key ability of future stations. A later addition was a three-light indicator to show if the pilot was on, right or left of course.
A September 12, 1925 Air Service News Letter describes these developments and stated “perfected, the Radio Beacon is bound to be of inestimable value.” Pilots stated it was a “very simple matter to remain on course.” It was another step closer, but still required the use of trailing wiring antennae and its cost of $6,000 per plane, or $89,000 in 2020 dollars, was prohibitive. Egge faced considerable internal headwinds. At the outset, Egge’s superiors told him to avoid “experiments that do not lead to anywhere,” and a later internal review found “little of importance was being done.” Egge was accused of misappropriation of funds and had to resign. The project was terminated but not before a paper was published - as such, many in the industry were aware.
The stage was set in 1926 when Congress passed the Air Commerce Act which established the US Government’s role in regulating but also furthering development of aviation by its creation of the Department of Commerce’s Aeronautics Branch. Both public and private sector aviation R&D boomed. At this stage there were published accounts and papers on the Monmouth Station, the Army Air Corps tests, the Bureau’s initial “directive” beacon as well as Scheller’s original patent – it would be difficult for anyone to now claim that they had a fully original ideal for LFR. Ford’s first range station would be finished later that year and in July 1926, the Bureau of Standards was given an expansive budget and a mission to find a suitable radio navigation system for the Department of Commerce. Events transpired quickly over the next few years:
Dated photographs and radio license in Ford Museum, and the excellent chronologies in Bonfires to Beacons and Beyond the Model T (see Resources) helped round out much of the timeline here and at top of the of the What it Was page.
The bottom line: Ford, through Mr. Donovan, finished the Army Air Service and Monmouth efforts to make LFR practical, which appear to have been more directly rooted in Scheller’s patent. Donovan’s hire and the Army’s presence at subsequent Ford tests would seem to imply a close working relationship between the two. Both the Army and Ford’s developments came after the Bureau’s nascent 1923 station that wasn’t ready for real-world service, and before its mature 1928 stations which incorporated all of their enhancements that made LFR truly viable. Certainly, there was wide collaboration across the field and new and old ideas circulated between groups. Arguably, many of the more logical improvements (e.g. vacuum tube radios) could have been intuited separately by Ford and the Bureau. But for whatever commonalties these factors led to in their final designs, Ford was the first to build a practical physical station that ordinary aircraft could use, the first to use it for a commercial purpose and, perhaps most importantly, it was first to the Patent Office. Afterwards, Ford clearly believed the Bureau and the Department of Commerce was using its innovations, but declined to enforce its rights.
It is also apparent that the US Army Air Service was the key driver behind LFR’s creation. They naturally turned to the Bureau for help in 1920 and kept its development going after the Bureau lost funding. When Ford and it resources presented itself as another avenue to achieve this goal the Army took the opportunity.
It’s not clear why the Bureau and later Department of Commerce accounts couldn't concede this. Even many modern accounts omit this history, likely as they simply relied on the Bureau’s records as gospel. It appears that the Bureau even started a PR campaign in mid-1927 in various newspapers to promote their position that they were “first.” Ford rebutted with its own articles and advertisements, culminating with its 1934 announcement that its patent was confirmed. The Bureau’s papers were instead focused on its successes and improvements possibly done to work around the patent, e.g. the 12-course and visual indicators that never came to be. Was this just a private versus public sector rivalry which led to the FCC’s ultimate push to get Ford out of the beacon business? Did the Bureau’s academic scientists, stymied by earlier funding cuts, have difficulty giving Ford’s well-resourced “commercial” engineers (and others) any credit for apparently making “their” earlier concept practical? On the other hand, the story of large corporations using the patent process to “appropriate” the honest work of others isn’t entirely unheard of. This is notwithstanding the fact that both parties heavily relied on prior innovations. A century later, it may be impossible to exactly ascertain what transpired, but it’s clear that Ford and the Bureau didn’t see events eye-to-eye. If anyone has any additional info that can clarify this history, please reach out to me!
Regardless, in the end, it was the US Government that awarded the patent to Ford and the US LFR network came to be only after Ford’s successful 1926/27 stations. Making the Low Frequency Range a practical reality was likely Ford’s most important contribution to aviation, outliving its famed Trimotor and the entire aviation division which shut down by 1933 due to the Depression. But, as with many inventions, Ford’s patent was rooted on prior efforts: every step that led to it heavily borrowed from previous ones. These included not only the Army’s 1923-1925 improvements and the Bureau’s early work, but Scheller’s original patent and the important addition of the Italian radio goniometers.
Ford’s achievement should also not diminish the Bureau’s many other accomplishments. Diamond would invent the first Instrument Landing System and made key improvements to the proximity fuse, one of the technologies vital for winning World War II. Dellinger had earlier helped popularize the word “radio” (vs. "wireless") in his efforts to standardize international conventions, would discover how solar flares impacted radio communications and would eventually have a lunar crater named after him. The College Park station was the birthplace of radio voice communication in aviation, it standardized LFR station design and the Bureau would continue to make important refinements to the system (including adding the British Adcock antenna). Renamed the National Institute of Standards and Technology (NIST) in 1988, the Bureau had gone on to develop the atomic clock fundamental to GPS, improved nearly everything from computers to missile systems and developed numerous innovations that are part of daily life from automobile standards to closed captioning systems on TV.
After nearly 30 years, the 1954 Civil Aviation Authority “Pilot’s Radio Handbook” would clearly acknowledge Ford’s role and patent.
Technically, the latter term is more correct as LFR did use both frequency ranges (demarcated at 300Khz) and more technical manuals tend to use this term. However, I think most would agree that “Low-Frequency Radio Range,” or just “LFR,” is much easier to write and pronounce and, in reviewing the source material for the website, these appear to be the most common terms likely for this very reason. We’ve elected to us it here for simplicity and consistency. “Four Course Radio Range” appears to be second, and “Adcock”, “LF/MF” and “A/N” Range while frequently used and also correct, would appear to all tie roughly for third place.
No, the 100-mile range of LFR meant that its use was restricted to land and the immediate coastal waters within that limit. Even modern VOR’s have a maximum range of 200 miles and the most powerful NDB’s were reliable up to only 500 miles or so. Before World War II, dead reckoning (estimating position based on time, direction, aircraft speed and the effects of wind) and celestial navigation were the only choices over oceans or other remote reaches of the globe. Pan Am Clipper pilots, and others that forged early international routes, became legendary by their necessary mastery of both.
Towards the end of the war in 1943, LORAN (see above) and its 1,000-mile plus range was able to provide coverage along the major transoceanic Atlantic & Pacific routes for both maritime convoys and aircraft. Coverage was expanded during the 50’s and 60’s and the user base grew when surplus first-generation "LORAN A" receivers flooded the market after second generation "LORAN C" became operational in the late 50’s. By the 70’s and 80’s oscilloscopes and vacuum tubes gave way to microelectronics and receivers became cheap and widely available. GPS pushed LORAN to obsolescence with the last stations shut down in 2015; however, as nations recognize the vulnerability of GPS, there is discussion of reviving a modern version called "eLORAN."
Nazi Germany utilized Elektra-Sonnen or “Sonne” (see above), which had a nearly equal range, in the North Sea and Eastern Atlantic after 1940. The British also clandestinely learned how to fully utilize it for their operations, going so far as to supply one Spanish station with much needed repair parts as Germany was forced into retreat at war’s end. After the war, the Allies appropriated and rebranded the system as "Consol," its British wartime code name. It became a popular postwar navigation option in Europe (the last station going off air in 1991) and was established at a few other locations across the globe.
Developed in the 1950’s for ballistic missiles, Inertial Navigation Systems (INS) incorporate a guidance computer that monitors sensitive gyroscopes and accelerometers to continuously calculate a vehicle’s location from a given starting point; in essence, highly accurate electronic dead reckoning. It requires no external references or radio signals which is highly advantageous for military applications from aircraft to submarines. Its precision was a function of “drift” over time but could provide about 5-mile accuracy after a twelve-hour flight. Its expense originally restricted it to the armed forces and larger commercial aircraft which began to commonly deploy it in the 1970’s. However, since the 1990’s miniaturization has greatly reduced the size and cost and it can now be found paired with GPS in many modern cockpit avionic suites, where each system can serve as check on each other to improve accuracy and consistency. Similar, less accurate systems can now be found in everyday products ranging from smartphones to automobile GPS systems.
Mr. Donovan did not appear to leave a legacy of scientific papers, articles and Wikipedia entries like some of his contemporaries referenced on this site; however, given his key role in the history of LFR we thought we should attempt to develop a biography for him. Thanks to sources such as Ancestry.com we can distill some details of his life, family and career:
Perhaps low key, but it appears he was an earnest family and career man blessed with a long life. It would be great to find out more of this man’s story beyond these data points. If anyone can provide any more details on Mr. Donovan please reach out to me.
Fan markers stations (type “FM”) were fairly simply structures, each consisting of small shed (perhaps 10’x 10’) containing a 100-watt transmitter with a row of horizontal dipole antennae either directly adjacent or on the roof. The entire footprint could easily fit within a 20’ x 80’ area. In urban areas they could be part of other structures. Like a Z marker this antenna projected a 75 Mhz signal upward, but with greater horizontal spread, to either form a lens shape, or a “dog bone” shape that was more pinched in the middle at the airway to provide a more precise marking of station passage. The nominal size marked on charts was 3 x 12 miles at 3,000 feet; however, the signal spread to over 6 x 20 miles at higher altitudes.
Their locations are very difficult to find for two reasons: (a) the locations on the charts were shown by the broad 3 by 12-mile shaded regions with unmarked center points and (b) the fan markers’ smaller size make them difficult to distinguish from other small structures. It was sometimes hard enough finding something as large as a range station on early aerials. Only the clearest aerials would likely show a fan marker station and their antennae, assuming that you find somehow found the exact location and pick it out from other surrounding buildings and ground clutter. If researchers need to locate a fan marker, we’d recommend digitally overlaying the sectional chart over an historic aerial to identify potential candidates.
Oh yes! The development of LFR regularly received news and media coverage during the 20’s through the 40’s, often on the front page. Especially during the early years both aircraft and radio and were still considered novelties. The press covered the barnstormers, inventors and explorers that constantly pushed the envelope of both technologies, but the public was especially captivated by the news that aircraft could now “magically” fly through dark, cloudy nights guided only by a radio signal. It was a major technical achievement perhaps comparable to the way the emergence of home computers, Mars landers and iPhones were to later generations. Also, as covered above, both the Bureau of Standards and Ford weren’t shy about getting word of their achievements out via news articles and advertisements (we have 40+ articles from various major newspapers in our research files, and we did not attempt an exhaustive search). It’s hard to believe today, but in addition to appearing in popular media, there was even a “Flying the Beams” board game and the term “on the beam” became popular in the mid-20th century. As air travel turned into the mundane experience most of us now take for granted by the 50’s and 60’s, the coverage for even newer navigation systems generally faded into the rear pages and into more specialized publications.