In the movie Castles in the Sky (IMDB) they point out that Robert Watson-Watt worked in the meteorology (weather) (Wiki: MET) branch of the National Physical Laboratory (NPL). While there he developed a direction finding system utilizing an Adcock antenna (Wiki) combined with a Western Electric model 224 oscilloscope which gave instantaneous bearings to lightening strikes. This lead to automatic HF DF (Wiki: Huff-Duff). An advanced version of this system in the Elephant Cage (Wiki: Wullenweber) DF system that has a bearing in a fraction of a second.
This is very different from DF systems that require manual pointing.
Patents by Robert Watson-Watt.
The Last Elephant Cage - FLR-9
By listening using a very sensitive receiver the LO of a W.W.II vintage receiver can be tuned. For RAFTER the frequency of the transmitter was known (typically a specific Numbers Station (Wiki). The sensitive receiver would be tuned to 455 kHz above the transmit frequency (sometimes 455 kHz below).
From the Wiki page: "By accident, one such receiver for MI5 mobile radio transmissions was being monitored when a passing transmitter produced a powerful signal. This overloaded the receiver, producing an audible change in the received signal. Quickly the agency realized that they could identify the actual frequency being monitored if they produced their own transmissions and listened for the change in the Superheterodyne (Wiki) tone."
It's not clear what is learned and how the sensitive receiver is tuned? Let me know.
The idea of the SE950 was that ships in W.W.II could locate submarines by using RDF. The target signal might be a transmission or from the Local Oscillator (LO) from a receiver leaking out to the antenna.The YE-ZB system (http://aafradio.org/docs/YE-ZB.pdf) as described in History of Communications
-Electronics in the United States Navy, by Howeth,1963 (Ref 2), used 12 azimuth beams each of which sent out a Morse code letter. An omni directional receiver in a carrier based airplane would know the bearing to the carrier by the letter that was strongest.
Aircraft: "ZB" UHF adapter for RU receiver.
Aircraftcarrier: rotating YE transmit antenna at top of mast. Codes tied to Magnetic North, not ship heading.
This system was replaced by TACAN (Wiki).
1820004 Aerial navigation system and method, Kruesi Geoffrey Gottlieb, FED TELEGRAPH CO, 1931-08-18 - a 6 beam system.
One use for RDF is part of a navigation system where the transmitting beacon location is known. This might be a low frequency, high frequency, VHF or UHF. The ARN-89 is an example of a LF-HF RDF system and the Light Weight Beacon is an example of an LF beacon that can be backpacked to a known location.
Another application is the one Robert Watson-Watt first developed, knowing about lightening. The "StormScope" is just such an instrument.
The A-N Low Frequency Radio Range was introduced in 1928. The Link Trainer was to learn how to use this navigation aid, not to learn to fly.
FAA: Flight Inspection History - checking various radio aids to navigation
This was made by Bendix. It covers the low and medium frequency bands.
1892151 Direction finding system, Hyland Lawrence A, Wired Radio Inc, Dec 27, 1932, 342/445, 343/728 - loops & sense whip, switchable unidirectional or bidirectional
Note sense antenna (1) used to eliminate ambiguity of loop antennas (6, 7).
1981884 System for detecting objects by radio, Hyland Lawrence A, Taylor Albert H, Young Leo C, Nov 27, 1934, 342/27, 367/128, 342/453, 340/991, 342/407 -
bi-static RADAR, depends on re-radiation rather than reflection since the frequency is much lower than current RADAR systems (i.e. probably HF).
2144309 Radio apparatus, Hicks Charles William, Bendix Radio, App: 1935-07-12, Pub: 1939-01-17, 342/443 116/280 342/449 116/302 455/274 -
2144310 Radio apparatus and method of manufacture, Hyland Lawrence A, Bendix Radio Corp, Jan 17, 1939, 343/842, 343/866, 29/605, 29/602.1, 343/872, 403/270
Note using insulating spacers (5) to keep wires separated from eachother and from the metal tube reduces capacitance which improves operation.
2159379 Radio antenna, Hyland Lawrence A, Bendix Radio Corp, May 23, 1939, 343/705, 343/872, 123/41.56, 244/1.00A, 343/866 - shielded loop built into a Townend ring (Wiki). Note even though the cowling is close to the spark plugs, the shielding stops the ignition noise.
Another use might be when an aircraft is involved in Search And Rescue (Wiki: SAR) where the beacon transmitter is in an unknown location. Survival Radios such as the PRC-90 transmit on known frequencies so the aircraft direction finder system only needs to operate on a limited number of frequencies.
Modern aircraft ejection seats contain a beacon transmitter, similar to the Vietnam era URT-33. Also built into aircraft there are locator beacons (Wiki) that are activated by a crash. Locating a downed aircraft is a problem that's not been solved as of 2015. The case of MH370 (Wiki) is troubling. The crash type beacon would be ineffective if a plane crashes into water because it will be under water in a very short amount of time. Although an improved crash beacon could be made (or probably already exists) that would eject from the aircraft and float to the surface. The ultrasonic Underwater Locator Beacon (Wiki: ULB) only has enough battery life to work for a month. So in the case of MH370 where the crash location could be in a huge area the battery had gone dead by the time the search location was narrowed. There needs to be improvement in the ULB. One area is so that standard Sonobuoys can detect it's signal. The existing signal was designed for optimum range when a very specialized ULB receiver is used. But in the case of MH370 where no one knew where to look that's of no value. But there are a huge number of sonobuoys all over the globe and the related equipment and personnel trained to use them.
There has been talk about live streaming aircraft data so that a plane in trouble would be recognized before it crashed, but that's not practical because if every plane aloft or moving on the ground was streaming data there would need to be a system that could (1) have enough bandwidth and (2) process that large volume of data in real time. A more practical system would be to put a box between the airplane and Flight Data Recorder (Wiki: Black Box) that would look for signs that a crash was likely. The problem is if the algorithm is too sensitive there will be a lot of false alarms and if too rigid it may not transmit enough information prior to the crash. Note this system would probably be put out of action the instant of a crash.
2020 June: the ADS-B beacons (Wiki) might be the answer if it's possible to have a satellite monitor the oceans?
Here's an idea I sent to the FAA:
"A simple solution might be to make an ADS-B transponder with internal rechargeable battery in an enclosure that's strong enough to contain an internal explosion and or fire caused by it's own battery. This would allow the crew to turn off it's external power, but not turn off the transponder function. The battery would be charged from the aircraft electrical system and there would be signal from the transponder if it's battery state was low. That signal can be monitored both by the crew and anyone receiving it's signal. The battery needs to have enough capacity so that the beacon can operate for more time than the plane it's in. Rather than just using the internal battery to replace the normal external power when the external power is off the transponder would go into a mode that depends on internal sensors. Part of this battery mode would be a signal saying it's on battery power. If a combination of sensors all say the plane is stopped on the ground then the transponder would turn off it's internal battery, but even then would run if external power was applied."
AAF Radio: DU-1 -
The frequency band for TACAN is 916 to 1215 MHz which includes IFF and ADS-B.
Wiki: Transponder, Modes, IFF (used Chain Home radar as trigger,not reliable), IFF2 (pre Magnatron based RADARs), IFF3 (157 - 187 Mhz), the Mk X IFF introduced 1030 Mhz for interrogation and a reply at 1090 MHz. The separation of 60 MHz means an LO at 1060 gives a 30 MHz IF for both Rx and Tx thus allowing the use of very common 30 Mhz IF equipment, ADS-B,
Replaced the Ze-ZB system (see ships above). TACAN systems can be installed on ships or pretty much wherever they are needed. But I'm guessing (2020) that as of the common use of ADS-B beacons and GPS the use of TACAN may decline.
The Wiki mentions there's no provision for stealth or crypto. That's to say the TACAN can be used by an enemy for their own use, or to attach the TACAN station.2232096 Radio direction finder, Francis W Dane, 1941-02-18 -
2468109 Direction finder,Avery G Richardson, Arbor G Everhart, Federal Telephone and Radio Corp, 1949-04-26 - motor driven & oscilloscope
3185988 Navigation bearing indicator system, Conrad D Ramalho,
Hoffman Electronics Corp,1965-05-25 - TACAN receiver
During W.W.II there were HFDF systems called Wullenweber (Wiki) FLR-9, Circularly Disposed Antenna Array or AN/FRD-10 (Wiki). In these systems which started off using a motor driven high speed scan and later upgraded to solid state beam rotation a very short transmission was all that was needed to get a good bearing to the source. This eliminated the cover that was provided by burst transmission like the GRA-71 that transmitted a message at 300 Words Per Minute instead of maybe 15 WPM for a manual Morse transmission.
The Army has a number of DF systems to locate enemy ground radio transmitters, for example the PRD-1 HF Direction Finding Radio used in Korea and Vietnam, Radio Receiving Set AN/TRQ-23 which uses the OE-4/GR antenna group. This system uses a motor drive to rotate the DF antenna and a CRT to provide bearings.
The Drop Zone Assembly Aid System (DZAAS) is a directional receiver worn on the wrist the points to a package on the ground that's arrived by parachute.Key, Object & Pet Location Tags are a new class of devices. Most work in conjunction with a smart phone and can help in locating something. Most of them do not depend on direction finding, but rather proximity between the tag and smart phone.
I have a couple of Black Boxes that are in machined aluminum boxes with water proof sealing that probably good to very great depths, i.e. they are the most indestructible electronic products I've ever seen. Not only could a tank drive over them but also they are immune to high levels of shock and vibration. They transmit a narrow pulse that all my receivers will not receive because a matched detector would require a much wider bandwidth than commercial or military receivers use, so the signal is very stealthy. I'm sure there's a directional receiver that works with these to help someone find whatever is attached.
They can have systems that are similar to the Wullenweber only at much higher frequencies. This could be used to locate other ocean going vessels or land based radio transmitters.
Anti Radiation Missiles (Wiki: ARM) are designed to fly into a source of radiation like would be used on a ground to air weapon system. For example the Shrike and HARM.
Many law enforcement agencies use LoJack (Wiki)
receivers on their cars. The cars use 4 roof mounted
antennas that work in a pseudo Doppler mode to provide a
There are also vehicle beacons that allow a tracking vehicle to follow without being in a direct line of sight. But I expect these have been replaced by tracking devices that combine a GPS receiver with a cell phone.
direction finder" exact phrase.
Quick Search for Class with all years selected. CCL/342/443, also: 342/436
Quick searchfor Class with all years selected. CCL/342/$
Weston Model 602 Left-Center-Right meteralso see Weston Model One and other early galvanometers
1579849 Pointer for electrical measuring instruments, Edward F Weston, Weston Elec Inst, 1926-04-06, - needle for meter movement.
1635595 Electrical measuring instrument, E.F. Weston, 1927-07-12, - meter movement
1661214 Zero corrector, Carpenter Grant, Weston Electric Inst, 1928-03-06, - meter zero adj
of US ILS)
Electric indicator for comparing field intensities, Kramar
App: 1932-12-13, Pub: 1936-06-23, - plane on or off course
Magic Eye Tube & Cathode Ray Tube
Cathode ray device, DuMont
Allen B, DuMont
Labs, App: 1932-05-28, Pub: 1937-11-09, 334/33;
313/107.5; 315/375; 327/600; 340/815.66; 116/263;
313/112; 315/409 - One pair of deflection plates, so not
Radio direction finder, Geoffrey G Kruesi, App: 1933-11-25, Pub:
1939-01-03, 342/436 342/439
two seat biplane. flexible shafts for loop rotation and loop tuning as well as radio tuning.
What Radio Direction Finder is this. Let me know.
See Army Air Force Radio: SCR-AE-183 and scroll down to:
Flight, April 11, 1935, pg 400:
An American "Radio Compass"; The Kreusi Type which is the Key Unit in the U.S. Army Air Corps Blind Landing System.
Thanks to Mike KC4TOS for this link.
AAF Radio: Bendix 1941 Brochure - SCR-242 (MN-26) 1937 manual -
Thanks to Bart, K6VK
|Sequential patents, all issued on Sept 26,
1939 to Pan Am
2174014 Direction finder, Ferris W Sullinger, Hugo C Leuteritz, Pan Am, 1939-09-26, 342/440; 333/124; 333/5; 342/437 - improvements on Adcock (Wiki) DF system by improving it's balance relative to ground and eliminating pickup from the horizontal wiring.
2174015 Direction finder, Ferris W Sullinger, Pan Am, 1939-09-26, 342/440; 342/437; 333/124 - Quad vertical dipoles "Adcock type"
2174016 Direction finder, Ferris W Sullinger, Pan Am, 1939-09-26, 342/440; 342/437 - uses balanced twistep pair to get vertical dipoles to center of array, but key is the use of tubes
2174017 Goniometer, Ferris W Sullinger, Jr Charles W Winter, Pan Am, 1939-09-26, 336/87; 336/208; 235/61PG; 336/125 - "electrostatic and electro-magnetic symmetry"
Distance measuring system, Francis
H Shepard, RCA, App: 1937-10-29, Pub; 1943-11-09, 367/95;
73/384; 235/414; 331/64; 331/168; 331/170; 331/174;
342/88; 367/114 - Fig 1 -4 & 7 - 9 audio, Fig 5
& 6 RF. Plate current depends on distance.
This may be the first patent for this simple type distance measurement?
Why does the plate current vary with the distance?
Calls patents:2254943 Radio direction finding, Galle Jean Baptiste Paul Henri, Jaeger-Aviation, 1941-09-02, 342/436; 332/173; 336/170; 336/182; 336/184; 336/212; 336/233; 342/439; 336/165; 336/178 - Crossed loops CRT display, similar to Robert Watson-Watt lightening system
GB252263 - 252,263. Watt, R. A. W. Dec. 3, 1924 - One loop (North-South) connected directly to the vertical deflection plates of a CRT and another (East-West) loop connected to the horizontal deflection plates of a CRT.
GB274344 - 274,344. Pilgrim, G. J. M. Dec. 9, 1926. Adding and subtracting apparatus - Not R.A. Watt
GB280235 - Telefunken Ges. f³r Drahtlose Telegraphie. Nov. 5, 1926, [Convention date]. Vacuum tubes. - a CRT like device with a sector shaped metal target or viewing screen.
GB380385 - 380,385. Directive wireless signalling. BRAILLARD, R., 55, Avenue Beau- Sejour, Uccle, MARIQUE, J., 249, Avenue Brugmann, and SOC. ANON. INTERNATIONALE DE TELEGRAPHIE SANS FIL, 13, Rue Brederode, both in Brussels, both in Belgium. April 2, 1932, No. 9514. Convention date, April 3, 1931. [Class 40 (v).] A direct reading radio compass comprises a mirror galvanometer 9
GB447238 - 447,238. Directive wireless signalling. MARIQUE, J., 36, Avenue Burnard, Uccle, and SOC. ANON. INTERNATIONALE DE TELEGRAPHIE SANS FIL, 13, Rue de Brederode, both in Brussels. Oct. 11, 1935, No. 28155. Convention date, Jan. 4. [Class 40 (v)] Relates to direct-reading radiogomometers of the type in which a Neon-lamp is used to indicate the critical points of maximum or minimum reception.
US1471406 see above.
Cited by 11 patents
2321606 Aircraft navigation instrument, William P Lear, Lear Aviation, App: 1940-05-15, Pub: 1943-06-15, 342/426; 342/443 -
Is this the SCR-269/LP-21 or some other manual rotation DF antenna?
Calls:2423437 Direction Finder, H.T. Budenbom (Bell Labs), filled: Aug 25, 1934, issued: Jul 8 1947, 342/369 -Short Wave DF receiver with CRT readout of difference between signals (not bearing)
2254943 see above
2286804 Radio compass, Frederick J Hooven, RCA, 1942-06-16, 342/436; 342/439 - single loop and steer Left-Right indicator.
2279151 see: Radar Warning Receivers\Panoramic (Radio Corp or Labs)
2159754 Tuning element for broadcast receiver sets, Wohlfarth Otto, AEG, 1939-05-23 - "On the other hand, Variometers have been disclosed in the prior art in which changes in in ductance are effected by variation of permeability rather than the shifting of an iron-core. The said change in permeability is obtained by varying the biasing magnetization of the iron coils. For instance, an auxiliary winding wrapped on the iron-core could be connected with a source of voltage existing in the set, the current caused to flow through the said auxiliary winding being regulated by a variable resistance or potentiometer."
Popular Mechanics1931 Planes are Landed by Radio when Fog Hides Field. "Airplanes can be landed safely by special radio guidance even when dense fog shrouds the field. Transmitting and receiving apparatus developed by the Bureau of Standards make it possible for the pilot to tell by indicators if he is on the proper course, when he reaches the boundary of the field and if he is sending the ship down at the right angle of glide to make a safe landing. A visual pointer, actuated by radio beams, shows the proper curve to make at landing and tells if the plane is too high or low for safe approach. The signal is loud until the boundary is reached and stops when crossing it."2454768 Direction Finding Antenna System, G.S. Burrroughs (Fed Tel & Radio Corp), Nov 30 1948 - "H" Adcock type system with sense antenna
Cites2684480 Permeability goniometer, John M Tewksbury, Alfred A Hemphill, Bendix Aviation, 1954-07-20, 342/436; 342/435; 342/440 - East-West, North-Sount & Sense antennas, goniometer with no moving parts.
Calls:2656536 Oscillographic plotting system, Robert W Lockhart, Stewart Warner, 1953-10-20, 342/428; 455/130 - motor driven loop and CRT
2208378 see above
2213273 see above
2263377 System for indicating the direction of propagation of electromagnetic waves, Busignies Henri Gaston, Bac Fernand, International Standard Electric Corp, 1941-11-18, 342/429; 367/120 - spinning antenna and CRT/deflection. See Background above. Cited by 44 patents.
2380929 Indicating system particularly for the measure of angles, Ahier Jean, Hardy Rene, App: 1941-05-17, Pub: 1945-08-07, 342/429 - CRT electrical commutation
2403727 Direction-finding system, Arthur V Loughren, Hazeltine Research, App: 1941-11-10, Pub: 1946-07-09, 342/436; 342/439 - feeds signals into antennas = complex
2407281 Radiated-signal direction finder, Johnson John Kelly, Harold A Wheeler, Hazeltine Research, App: 1941-12-18, (W.W.II), Pub: 1946-09-10, 342/429; 315/378 - 100 to 156 MHz coverage, CRT display, cited by 15 patents.
2408039 see above.
Calls:2761134 Means for operating antennas, John M Tewksbury, Alfred A Hemphill, Bendix Aviation, 1956-08-28, 342/434; 342/436 - Adcock array has the look and feel of my Goniometer
2361436 Radio direction finder, Paul B Taylor, App: 1937-11-18, Pub: 1944-10-31, 342/437; 342/439; 342/448 - CRT
2365118 Electrical apparatus, Strafford Frederick Wentworth, AC Cossor, App: 1941-09-13, Pub: 1944-12-12, 342/432; 343/812 - remove ambiguity w/o sense ant.
2407659 Phase comparison system, Fuchs Morton, Federal Telephone and Radio, 1946-09-17, 342/430 - not clear if manual or CRT?
2427660 Radio direction finding system, Roger B Colton, Rex V D Corput, Eleanor T Watson, App: 1944-06-27, Pub: 1947-09-23, 342/428 - CRT
2474268 Radio-frequency in-phase indicator, Marchand Nathan, Federal Telephone and Radio, App: 1945-07-03, Pub: 1949-06-28, 324/84; 324/85; 342/439; 333/125 - phase comparison
2476977 see above.
2656536 see above.
Ref 1 Secret Weapon by Kathleen Broome Williams (ISBN: 1-55750-935-2) - History of HF-DF
Ref 2 History of Communications-Electronics in the United States Navy, by Howeth,1963 (free)
Ref 3Ref 4 An instantaneous direct-reading radiogoniometer, R.A. Watson Watt & J.F. Herd, IEE, Vol 64 (1926), pages 596-622 or (611-622) - operated between 200 and 400 kHz. (see: SkyScan Severe Thunderstorm Detector which operates on 700 & 1400 kHz)
Ref 5 Journal of Intelligence History: Shore High-Frequency Direction-Finding in the Battle of the Atlantic: An Undervalued Intelligence Asset - mentions Ref 4 above
Ref 6 Scottish Science Hall of Fame: Robert Watson-Watt (1892-1973): An instantaneous direct-reading radiogoniometer - Page 614 -
Ref 7 FCC Radio Intelligence Division (RID) - historic info - also see Aperiodic receivers on my Radar Warning Receiver web page.
Ref 8 CIA: The U.S. Hunt for Axis Agent Radios - also see my Hollow Nickel Spy Case web page.
Ref 9 The History of the Radio Intelligence Division Before and During World War II, 1940 - 1945(pdf), (Google search page, NSA.pdf)
Ref 10 YouTube: Patrolling the Ether, (echo in sound)
Ref 11 TM 11-487D, Radio Direction Finding Equipment, Jan 1951, (Google), 27 pages.
Ref 12 Radio Material School, Chapter 3, Aircraft Radio Direction Finders (pdf) - The RDF-1-A has a resonate loop driving the grid of VTa, a wire antenna with a pot feeding VTb with a variable cap connecting the two tube plate circuits and a fixed cap feeding the receiver. Similar to the DU-n series of 1' OD loops on a box.
0.54 - 30
0.25 - 1.5
5 Verticals 10,060
0.2 - 18
0.55 - 30
2 - 20
5ea Crossed "U"
1.5 - 30
2 sets of 5 crossed "U:
1 - 3
0.1 - 1
0.1 - 65
18 - 65
65 - 156
0.015 - 145
Many on Masts
Ref 13 Appendix M. U.S. Naval Radio Equipment - 4. The Radio Direction Finder: includes SE 950
Ref 14 History of Communications-Electronics in the United States Navy, 1963 (html, pdf)
The Poppy satellites (Wiki) were early (1962) ELINT (Wiki) satellites, some of which may have flown in formation.
Naval Ocean Surveillance System (Wiki) satellites flying in formation can locate Russian ships at sea. First launch in 1976.
In the past decade I've read that China has a very similar system that can locate US ships at sea. That article also stated that China could use the same missiles used for nuclear weapons to launch a missile with a conventional warhead. This is a problem because at launch we will not know what type of warhead is being used. The time between a ship detecting that the missile is coming straight down and the time the conventional explosive destroys the ship is a few seconds. Note this is much less warning time that is available when an anti-ship missile approaches from the horizon.
A private company doing RF emitter location using three satellites flying in formation. Covers 144 Mhz to 15 GHz. This is part of Geospatial intelligence (Wiki).
8952847 System of geographical location of a radio signal transmitter located on the earth's surface, and associated method of distributed interferometry, Christian Peyrotte, Francis Martinerie, Jean-Baptiste THEVENET, Thales, 2015-02-10, 342/424 - the satellites shown in Fig 1 look very much like those shown at: HawkEye360/Technology.
Restricted Training Film 1-328, Aerial Navigation, 1942, 28:58 - Airways Flying -
The Chum Bucket - Marine Radios - Marine Radio Direction Finders -Back to Brooke's Products for Sale, Military Information, Electronics, Personal Home, PRC68.com page
USASADF (United States Army Security Agency Direction Finding): Radio Fingerprinting - RFP - identifying transmitters (giving each a serial number).
FAS: PRD-12 - HF/VHF/UHF
An Evaluation of Short-Based Radio Direction Finding 1978 - for VHF EPRIB beacons with analysis of Doppler and other systems
Army: More aerial intelligence systems used during Vietnam War - various platforms and bands
: United States Army Airborne Radio Direction Finding Operations -
General Dynamics: AN/MLQ-44 Prophet-Enhanced SIGINT -
page created 5 Oct 2009.