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Low-Frequency Radio Ranges

Thomas Johnson sent the first two articles, and is a dedicated hobbiest in the field:
Low-Frequency Radio Ranges Tom Johnson, June 7, 2010
Old Transmitter Tom Johnson, November 10, 2010
Last operational Range Instrument Approach David Hykle, April 21, 2011
1971 FAA Beacon drawing LaFarr Stuart, Sept 3, 2011
Beacon Image and bulb changer Tom Johnson, Sept 3, 2011
More interesting pages in the FAA document Tom Johnson, Sept 3, 2011
1928 airway beacon towers advertising brochure from IDECO Tom Johnson, Sept 6, 2011
Aircraft Owners and Pilots Association's AOPA Pilot magazine story about airway beacons Tom Johnson, Dec 29, 2011
Radio Frequency Comments and Updates Waldo Magnuson , Feb 18, 2012
and things kinda escalated outa control ;-)) - OK, Thomas Johnson keeps a eye on things.
These frequencies are a factor of 10,000 lower than what I played with.

Low-Frequency Radio Ranges, June 7, 2010

Low-Frequency Radio Ranges

Tom Johnson

The article I wrote for the July, 2009 Touch & Go, "Airway Light Beacon Archaeology," explained my interest in finding the remnants of the beacons that guided pilots at night from the late 1920?s into the 1950?s. During that same period, pilots were guided in instrument flight, and in daytime visual flight, by the Four-Course, Low-Frequency Radio Range. The beacons and radio ranges were the navigation aids (or navaids) that were indispensable in enabling the airplane to evolve from being a marginal, fair-weather, daytime-only supplement to America?s transportation system to becoming a major, all-weather transportation provider in the course of 20 years.

The first experiments in using radio for both air navigation and two-way communication were conducted by the U.S. Air Mail Service in 1919 and 1920 but were soon discontinued. The establishment of the Aeronautics Branch in the Department of Commerce in 1926 brought renewed efforts in radio communication and navigation. The first seven two-way communication stations, developed by the National Bureau of Standards, were installed by October, 1928. That system expanded to 68 stations, spaced approximately 200 miles apart, by mid-1933.

The Low-Frequency Radio Range (LFR), also known as the Four-Course Radio Range, the A-N Radio Range or the Adcock Radio Range, was developed in the late 1920?s after some unsatisfactory experiments with navigation by both ground-based and airborne radio direction finding. One account attributes development of the LFR to radio engineers of the National Bureau of Standards, borrowing from European systems with improvements contributed by the U.S. Army Signal Corps.1

Another account states: "Late in the fall of 1926, the Ford Motor Company was engaged in ferrying air freight between its Chicago and Dearborn airports. The first of the famous Ford Tri-motor planes was placed on this run early in 1927, and it was in this year that a young Ford radio engineer named Eugene S. Donovan patented the first four-course, loop-type, low-frequency radio range. Two of the radio ranges were installed by the Ford Co., one at their Chicago Lansing Airport and one at the Dearborn Ford Airport. Both proved quite successful in improving the bad weather reliability of the cargo flights. The following year, after intensive and exhaustive tests, the Federal Government began installing a vast chain of LF/MF ranges crisscrossing the Nation to provide radio highways of the air. For each installation patent permission was given, without royalties, by the Ford Motor Co. so that these ranges could be installed in the public welfare.2

Oakland, CA

Bozeman, MT

Whitehall, MT

Wendover, UT

Whitmore, CA

Fort Jones, CA.

Irrespective of how the LFR was developed, it was soon considered "indispensible" to the development of aviation. Some who considered Ford the developer of the radio range proclaimed it to be a more significant contribution to aviation than Ford?s famous Tri-motor airplane.

The four-course radio range used two loop antenna systems to transmit two overlapping figure-eight patterns. Transmission frequencies were in the 200 to 410 kHz range with some military LFR?s operating at as high as 536 kHz. One pattern transmitted a Morse code letter A (? ? ) and the other, with the pattern oriented at approximately right angles to the first, the code letter N (? ?). The timing of the code transmissions was such that when the two transmissions were received with equal strength, where the two directionally-transmitted patterns overlapped equally, the interlocking A and N code tones produced a steady tone. These four areas, each about three degrees wide, defined the four courses or "beams" of the station. A complete description of the LFR and how it works, with sample audio recordings, may be found in the online Wikipedia article titled "Low-frequency radio range." Another article about the LFR and a new high-frequency re-creation of a LFR in Tennessee may be found in Barry Schiff?s Proficient Pilot column on page 30 of the June, 2010 issue of AOPA Pilot magazine. The article is available to all at the website. Search for "Play it by ear" then click on "AOPA Online: Proficient Pilot."

The beams of the Low-Frequency Radio Ranges defined the airways of the 1930?s to 1950?s, designated Red or Green for east-west routes (airway Green 3 extended east from Oakland to Newark, NJ) and Amber or Blue for north-south airways. At their peak, in the mid to late-1940?s there were over 440 LFR sites in the 48 states, Alaska and Hawaii. By August, 1960, installation of the VHF omnidirectional radio range or VOR had reduced the number of LFR sites to 258. Some LFR?s were converted to non-directional (radio) beacons or NDB?s using the one central antenna tower of the previous LFR. The last remaining LFR?s were shut down in the 1970?s.

Searching for vestiges or remains of the low-frequency radio ranges, I determined the first task of a "LFR archeologist" is to find where the ranges had been located. The best sources of approximate locations are aeronautical charts of the 1930?s to the 1950?s. Many of these charts, especially from the World War 2 years, are available on eBay because so many were produced for pilot training. Another good source, given to me by an instructor at Utah State University in 1961 is the August, 1944 issue of the Army Air Forces Radio Facility Charts booklet that includes the latitudes and longitudes of all LFR stations.

From the chart?s approximate positions it is often possible to determine an exact position using a National Geodetic Survey online search tool to find possible survey marks. This process found precise survey marks still on record for 10 of California?s 35 LFR sites. An online search of topographic maps located 8 additional LFR?s, six on the large-scale (1:24,000) maps. Searching the area on Google Earth and Bing Maps aerial photos has sometimes, when structures have be undisturbed, been the only means of exactly locating a LFR site. This is possible since, unlike the case with airway beacons, most LFR installations covered a 600 by 600 foot or 8+ acre site. On the site there were typically five approximately-120-foot antenna towers, mounted on concrete bases, plus a central building housing the transmitter and a standby engine/generator set. One tower was at the center of the site near the building with the other four towers at the edges of the square area.

The next, and potentially most-exciting, step has been to search the aerial photos to see if any features of the LFR still remain today. In the greater Bay Area, ranges were located at near the Hamilton, Moffett, Oakland, and San Francisco airfields. At Hamilton, the range was later converted to a non-directional radio beacon and the central building and center antenna tower are still standing. Aerial photos (search lat/lon: 38 05.50, -122 30.48) also clearly show the bases of the four outlying antenna towers. The Oakland site, west of Doolittle Drive and north of the north field or original airport, has not been reused and the concrete foundation slab of the central building can be seen in aerial photos. Exploration at the site, on the ground, revealed electrical junction boxes, partially-buried wiring extending to an outlying antenna tower site and broken red glass from obstruction light covers. It was impossible to determine exact locations of the San Francisco and Moffett sites and, in any event, the areas appear to have been reused or built over.

Features of seven other California LFR sites are still visible from the air! The most intact site, which is possibly the most-undisturbed in the nation (!), is near Fort Jones, about 31 miles WNW of Mount Shasta and 31 miles south of the Oregon state line. The aerial photo shows the central building and four of the five antenna towers still standing. After driving by on a trip to Seattle, I made contact with people in the local Scott Valley Pilot?s Association to arrange a visit to the LFR site. They were very hospitable and arranged with the property owners for a visit to the site in exchange for my speaking about airway beacons and low-frequency ranges at their monthly barbecue. The ranch owner related that when the CAA had leased the site in the 1930?s his father had signed an agreement that the government would remove all structures when they were no longer used. When the range was shut down in 1965, however, the FAA offered a new agreement that, in exchange a small payment, the government could simply walk away. Hence, we have a unique piece of aviation history in far Northern California!

Another case of "walking away" appears to be at the Whitmore LFR site, in a very rural area about 18 miles east of Redding, CA. This range was commissioned in 1944 and, apparently due to the efforts to conserve steel during WW2, used wood utility poles for antenna towers. A number of the pole-to-pole antenna wires were still in place when I visited the site 64 years later! Another northern-California LFR commissioned during 1944 served the Alturas Army Airfield. The Google Earth/Maps view (search lat/lon: 41 34.688, -120 42.922) clearly shows the Alturas central-building (or its slab), the five antenna-tower bases and even the supports for the cables from the central building to the towers! At Red Bluff, as at other locations, the central antenna tower is currently used by a non-directional radio beacon with the concrete bases of the four outlying antenna towers still in place in an open field. At some similar installations, such as Miles City, Montana, today?s radio beacon still operates on the same frequency as the 1940?s range station!

Driving to Montana in 2008 to explore airway beacons and discuss their current use in the state with Montana Aeronautics Division people in Helena, I was able to explore seven LFR sites in Montana, Idaho and Nevada. Five sites had red brick central buildings with glass-block windows, a 1930?s architectural fad. The site at Whitehall, Montana had interesting wood-post cable supports between the central building and each of the five antenna-tower bases. At Bozeman, the red-brick central building is easily accessible on the property of today?s airport.

On a 2009 trip to Utah, I explored the LFR sites at Fairfield, Plymouth, Salt Lake City and Wendover. At Wendover, I thought I would be able to walk about 100 feet across the salt flats to the base of an antenna tower but, on the first step, I sank ankle-deep into the "slush" beneath the surface! In the summer of 2010 I hope to visit seven sites in California, Oregon, Washington and Wyoming.



1 Komons, Nick A. Bonfires to Beacons: Federal Civil Aviation Policy under the Air Commerce Act, 1926-1938. Washington, D.C.: Smithsonian Institution Press, 1989 (page 155)

2 Pilots? Radio Handbook, C.A.A. Technical Manual No. 102. Washington, D.C. U.S. Government Printing Office, March, 1954 (page 44)

Old Transmitter, November 10, 2010
Simultaneous Radio Range & Telephone Transmitter - Type TSC - 200-400 KCS
Four-course, low-frequency radio range transmitter of the general type used for air navigation in the United States from the late 1920's to the early 1960's. This 1937 Westinghouse transmitter is identified as "simultaneous" because, unlike earlier versions, it was capable of transmitting the range navigation signals (A and N) and voice transmissions at the same time. This transmitter is displayed at the Oregon Air and Space Museum ( at the Eugene, Oregon airport.
The 805 vacuum tube graph is from

Front View
, 120 K Bytes
Hi res view, 1.3 megabytes

Data Plate

Vacuum Tubes inside front door w fan below

Tank Circuits - upper side view

Big Iron - lower side view

805 Tube Characteristics

Last operational Range Instrument Approach
David Hykle April 21, 2011
Hi Ed:

Just finished reading the neat article by Tom Johnson regarding Radio Range facilities. Great article ! Some trivia for you.... the last operational Range Instrument Approach procedure was located at Castlegar, British Columbia. I still have the original chart dated 1980 !


1971 FAA Beacon drawing - Sept 3, 2011
On Fri, Sep 2, 2011, LaFarr Stuart < > wrote:

Hi: A 1971 FAA description of Beacons and other airport lights is at:$FILE/150-5340-21.pdf (2.3 MByte)

In the Appendix, near the end, there are some drawings and some interesting details. I think the older Beacons were the 36" diameter ones.
It talks about a magnetic bulb changer.

Cheers, LaFarr Stuart

This is the four pages of the longer Appendix 1 which seems to be the interesting material found by LaFarr. 104 KBytes.

Beacon Image and bulb changer - Sept 3, 2011
On Fri, Sep 2, 2011, Thomas Johnson < > wrote:

While I was in Washington I made contact with an airway light beacon chaser that I met through the Montana State Aeronautics people (the only operators of airway beacons today). He took me to the Toledo, Washington airport. The airport beacon there (it was in the numbered airway beacon system) has been replaced by a more-modern unit and the original beacon and its motor mounted on a concrete pad on the ground. Kind of odd; why not store it away somewhere? The beacon was an old 36-inch model, probably from the late 20's or early 30's.

The interesting part was that the back side was open and it was possible to see and move the automatic bulb-changer. When a bulb failed, an alternate bulb would be moved into position and illuminated automatically. I can imagine how such a device might work but don't know for sure. I've attached two photos. The bulbs had two prongs that were inserted in the holes in the square receptacles. The bulb changed when the assembly pivoted about 20 degrees. Any ideas on how it would have functioned?

Tom J.

Toledo, WA Beacon
This may be the
36 inch Rotating Beacon
in four pages above.

Beacon Bulb Changer

LaFarr Stuart commented:

Interesting question about how the bulb changer worked. It had to detect the burned out filament, then switch the 2nd bulb into position.

The old GE (Telechron) electric clocks had an indicator that would turn red if the AC power failed. It was simply a small iron that was held magnetically when the power was on, when the power failed the iron was no longer held close to the clock's core magnet and it pivoted away from the core, and stayed there when the power was restored.

I would guess the power to the bulb went via an Iron cored choke, and when the bulb burned out the current would stop letting the mechanism swing the 2nd bulb into the focal point of the mirror.

More interesting pages in the FAA document
sent by Thomas Johnson - Sept 3, 2011

Page 8
The most interesting section is on page 8 where it speaks of the optical system of the 36-inch beacon and says "Upon failure of the first lamp, a magnetic lamp changer is provided to automatically throw in focus and connect to the power source a spare lamp. A telltale power circuit operates an indicating light when the spare lamp has been put into the operating circuit." The telltale light is then similar in function to the red indicator you mentioned in the electric clocks.

Page 17
The paragraph on page 17 about relamping the 36 inch beacon was also interesting in that it speaks of the reserve lamp and the operating and reserve receptacles. Also of resetting the lamp changer and then tripping and resetting it "several times" as a test.
four pages The Figure 1 in Appendix 2 shows some wiring at a "terminal block in beacon base" and indicates that the "obstruction lights" are the telltale. But it doesn't completely explain (at least to me) how the lamp changer and telltale work together.

1928 airway beacon towers advertising brochure from IDECO
from Thomas Johnson to LaFarr Sept 6

300 KB
LaFarr, a good idea to include Dennis. I recently came across this 1928 airway beacon towers advertising brochure from IDECO which may be of interest to Dennis, having worked with other IDECO products. I don't remember having seen it before.
Tom J.

Aircraft Owners and Pilots Association's AOPA Pilot magazine story about airway beacons - Dec 29, 2011
from Thomas Johnson
Airway Beacon Friends,

Would you believe that the January, 2012 issue of the Aircraft Owners and Pilots Association's AOPA Pilot magazine has a story about flying by the airway beacons? Yep, it does!

If you don't receive the paper copy, the direct link to the article is:

If that doesn't work for you, try going to the AOPA home page at:
Then scroll down to the image of the January, 2012 magazine cover (with a Pitts Special biplane) and click on it. Next, near the bottom of the page on the left, click on "Proficient Pilot."

The title of the article, "WUVHRKDBGM" mystified me at first although I should have recognized it as the nemonic for "When Undertaking Very Hard Routes Keep Directions By Good Methods" used to remember the sequence of letter codes flashed by the airway beacons.

It's good to see our airway beacons getting good press in 2012. It would have been good if the article had mentioned that airway beacons are still at work in Montana and that beacons and their associated structures have been restored in the Grants, NM area and at two museums in Oregon.

I hope you enjoy the article!

Tom Johnson

Radio Frequency Comments and Updates
Waldo Magnuson - Feb 18, 2012
In Tom Johnson's article "Low Frequency Radio Ranges" he mentions that at Miles City, MT the same frequency is used in the Radio Becon (NDB) as was used in the LFR in 1940.

At Spokane, WA the LFR at Felts Field was 365 kc in at least 1936 (i.e. 1936 Sectional Chart). This Radio Range was moved five miles to Marshal, WA to serve Geiger Field, Spokane, WA in the early 1950s. The LFR at Marshal was decommissioned and replaced by a NDB (same frequency 365 kc). The Marshal NDB was later moved back to on-field at Felts Field (maybe late 1980s) still retaining 365 kc.

In 2008 the Felts Field NDB was decommissioned and moved to the Deer Park, WA airport (DEW) about 15 miles north of Felts Field and retained the same frequency. So the frequency 365 kc has stayed operational in the Spokane area since at least 1936 and is currently operationat at Deer Park in 2012. The dates above were verified using Army, CAA and FAA Sectional Charts. Skip Magnuson

If you have comments or suggestions, Send e-mail to Ed Thelen and Tom Johnson

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