477:, working at the Admiralty Signal Establishment. As ships were equipped, a complex measurement series was carried out to determine these effects, and cards were supplied to the operators to show the required corrections at various frequencies. By 1942, the availability of cathode ray tubes improved and was no longer a limit on the number of huff-duff sets that could be produced. At the same time, improved sets were introduced that included continuously motor-driven tuning, to scan the likely frequencies and sound an automatic alarm when any transmissions were detected. Operators could then rapidly fine-tune the signal before it disappeared. These sets were installed on convoy escorts, enabling them to get fixes on U-boats transmitting from over the horizon, beyond the range of radar. This allowed hunter-killer ships and aircraft to be dispatched at high speed in the direction of the U-boat, which could be located by radar if still on the surface or ASDIC if submerged.
532:
distance from the loops about 1/2 of a wavelength away. When this signal was mixed in, the opposite-phase signal from this aerial would strongly suppress the signal when the phase is in the direction of the sense aerial. This signal was sent into the brightness channel, or Z-axis, of the oscilloscope, causing the display to disappear when the signals were out of phase. By connecting the sense aerial to one of the loops, say the north/south channel, the display would be strongly suppressed when it was on the lower half of the display, indicating that the signal is somewhere to the north. At this point the only possible bearing is the north-east one.
504:
288:
up the antenna in 1919 but had been neglecting it in favour of smaller designs. These were found to have very poor performance due to the electrical characteristics of the Slough area, which made it difficult to determine if a signal was being received on a straight line or down from the sky. Smith-Rose and
Barfield turned their attention back to the Adcock antenna, which had no horizontal component and thus filtered out the "skywaves". In a series of follow-up experiments they were able to accurately determine the location of transmitters around the country.
215:. Their system motorized the search coil as well as a circular display card, which rotated in sync. A lamp on the display card was tied to the output of the goniometer, and flashed whenever it was in the right direction. When spinning quickly, about 120 RPM, the flashes merged into a single (wandering) dot that indicated the direction. The team destroyed all of their work in the French office and left France in 1940, just before Germany invaded, and continued the development in the US.
387:
31:
528:, depending on the relative phases. The curve is rotated so that its major axis lies along the bearing of the signal. In the case of a signal to the north-east, the result would be an ellipse lying along the 45/225-degree line on the display. Since the phase is changing while the display is drawing, the resulting displayed shape includes "blurring" that needed to be accounted for.
448:(for security) and transmitted quickly. An experienced radio operator might take about 20 seconds to transmit a typical message. Had the UK been using B-T systems, the only system known to the Germans at the time, determining the location of such a transmission would have required considerable luck. With huff-duff, these messages were more than long enough to easily measure.
276:(NPL) Radio Section research site. Watt was involved in the Atmospherics branch, making basic studies in the propagation of radio signals through the atmosphere, while the NPL were involved in field strength measurements in the field and direction finding investigations. NPL had two devices used in these studies that would prove critical to the development of huff-duff, an
300:. Working with Jock Herd, in 1926 Watt added an amplifier to each to the two arms of the antenna, and sent those signals into the X and Y channels of the oscilloscope. As hoped, the radio signal produced a pattern on the screen that indicated the direction of the strike, and the slow-decay phosphor gave the operator ample time to measure it before the display faded.
452:
accuracy was relatively inefficient, so the fixes were not particularly accurate. In 1944 a new strategy was developed by Naval
Intelligence where localized groups of five shore-based DF stations were built so the bearings from each of the five stations could be averaged to gain a more reliable bearing. Four such groups were set up in Britain: at
520:
move up and down, so rapidly that it would appear to be a straight vertical line, extending equal distances from the center of the display. When the second channel is added, tuned to the same signal, the dot will move in both the X and Y directions at the same time, causing the line to become diagonal. However, the radio signal has a finite
358:" was installed on some of the fighters, at least two per section (with up to four sections per squadron). Pip-squeak automatically sent out a steady tone for 14 seconds every minute, offering ample time for the huff-duff operators to track the signal. It had the drawback of tying up the aircraft's radio while broadcasting its DF signal.
287:
The Adcock antenna is an arrangement of four monopole masts connected electrically to act as two virtual loop antennas arranged at right angles. By comparing the signals received on the two virtual loops, the direction to the signal can be determined using existing RDF techniques. Researchers had set
163:, in its most basic form simply a circular loop of wire with a circumference decided by the frequency range of the signals to be detected. When the loop is aligned at right angles to the signal, the signal in the two halves of the loop cancels out, producing a sudden drop in output known as a "null".
539:
For shipboard systems, the ship's superstructure presented a serious cause of interference, especially in phase, as the signals moved around the various metal obstructions. To address this, the ship was anchored while a second ship broadcast a test signal from about one mile away, and the resulting
377:
systems with the promise that CRT versions would replace them as soon as possible. This could be accomplished in the field, simply by connecting the existing antennas to a new receiver set. By 1940 these were in place at all 29 Fighter
Command "sectors", and were a major part of the system that won
535:
The signals received by the antennas are very small and at high frequency, so they are first individually amplified in two identical radio receivers. This requires the two receivers to be extremely well balanced so that one does not amplify more than the other and thereby change the output signal.
519:
The deflection of the spot on the oscilloscope display is a direct indication of the instantaneous phase and strength of the radio signal. Since radio signals consist of waves, the signal varies in phase at a very rapid rate. If one considers the signal received on one channel, say Y, the dot will
345:
The expedient solution to this was the use of huff-duff stations to tune in on the fighter's radios. Every Sector
Control, in charge of a selection of fighter squadrons, was equipped with a huff-duff receiver, along with two other sub-stations located at distant points, about 30 miles (48 km)
543:
Naval units, notably the common HF4 set, included a rotating plastic plate with a line, the "cursor", used to help measure the angle. This could be difficult if the tips of the ellipse did not reach the edge of the display, or went off it. By aligning the cursor with the peaks at either end, this
464:
in
Cornwall. It was intended that other groups would be set up in Iceland, Nova Scotia and Jamaica. Simple averaging was found to be ineffective, and statistical methods were later used. Operators were also asked to grade the reliability of their readings so that poor and variable ones were given
174:
In 1907 an improvement was introduced by Ettore
Bellini and Alessandro Tosi that greatly simplified the DF system in some setups. The single loop antenna was replaced by two antennas, arranged at right angles. The output of each was sent to its own looped wire, or as they are referred to in this
531:
This leaves the problem of determining whether the signal is north-east or south-west, as the ellipse is equally long on both sides of the display centre-point. To solve this problem a separate aerial, the "sense aerial", was added to this mix. This was an omnidirectional aerial located a fixed
303:
Watt and Herd wrote an extensive paper on the system in 1926, referring to it as "an instantaneous direct-reading radiogoniometer" and stating that it could be used to determine the direction of signals lasting as little as 0.001 seconds. The paper describes the device in depth, and goes on to
166:
Early DF systems used a loop antenna that could be mechanically rotated. The operator would tune in a known radio station and then rotate the antenna until the signal disappeared. This meant that the antenna was now at right angles to the broadcaster, although it could be on either side of the
540:
signals were recorded on a calibration sheet. The broadcast ship would then move to another location and the calibration would be repeated. The calibration was different for different wavelengths as well as directions; building a complete set of sheets for each ship required significant work.
451:
At first, the UK's detection system consisted of a number of shore stations in the
British Isles and North Atlantic, which would coordinate their interceptions to determine locations. The distances involved in locating U-boats in the Atlantic from shore-based DF stations were so great, and DF
304:
explain how it could be used to improve radio direction finding and navigation. Despite this public demonstration, and films showing it being used to locate lightning, the concept apparently remained unknown outside the UK. This allowed it to be developed into practical form in secret.
536:
For instance, if the amplifier on the north/south antenna has slightly more gain, the dot will not move along the 45 degree line, but perhaps the 30 degree line. To balance the two amplifiers, most set-ups included a "test loop" which generated a known directional test signal.
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Land-based systems were used because there were severe technical problems operating on ships, mainly due to the effects of the superstructure on the wavefront of arriving radio signals. These problems were overcome under the technical leadership of the Polish engineer
190:
All of these devices took time to operate. Normally the radio operator would first use conventional radio tuners to find the signal in question, either using the DF antenna(s) or on a separate non-directional antenna. Once tuned, the operator rotated the antennas or
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their location, and then relay that information to the control rooms. Comparing the positions of the enemy reported by the
Observer Corps and the fighters from the huff-duff systems, the Sector Commanders could easily direct the fighters to intercept the enemy.
71:
and their land-based headquarters. HF/DF was primarily used to catch enemy radios while they transmitted, although it was also used to locate friendly aircraft as a navigation aid. The basic technique remains in use as one of the fundamental disciplines of
87:
and listened for peaks or nulls in the signal to determine the bearing to the transmitter. This took considerable time, on the order of a minute or more. Radio operators could avoid being located by keeping their messages short. In HF/DF systems, a set of
511:
The basic concept of the huff-duff system is to send the signal from two aerials into the X and Y channels of an oscilloscope. Normally the Y channel would represent north/south for ground stations, or in the case of the ship, be aligned with the ship's
183:, the "search coil". The maximum signal was generated when the search coil was aligned with the magnetic field from the field coils, which was at the angle of the signal in relation to the antennas. This eliminated any need for the antennas to move. The
195:
looking for peaks or nulls in the signal. Although the rough location could be found by spinning the control rapidly, for more accurate measurements the operator had to "hunt" with increasingly small movements. With periodic signals like
107:. Its role in intelligence was not developed until the late 1930s. In the early war period, HF/DF units were in very high demand, and there was considerable inter-service rivalry involved in their distribution. An early use was by the
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It was Watt's continuing desire to capture the location of individual lightning strikes that led to the final major developments in the basic huff-duff system. The lab had recently taken delivery of a WE-224 oscilloscope from
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knew that radio direction finders could be used to locate its ships at sea when those ships transmitted messages. Consequently, they developed a system that turned routine messages into short-length messages. The resulting
115:
of interception control, while ground-based units were also widely used to collect information for the
Admiralty to locate U-boats. Between 1942 and 1944, smaller units became widely available and were common fixtures on
338:(later Royal Observer Corps) for visual tracking in this area. While the Observer Corps were able to provide information on large raids, fighters were too small and too high to be positively identified. As the entire
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before they vanished. All that could be determined was an average location that produced the best signal over a long period, incorporating the signal of many strikes. In 1916 Watt proposed that a
507:
Huff-duff aerial (enlarged) on a
Pakistani frigate. The two (square) antenna loops are formed by the diagonal rods at the top of the structure with the rods below for reinforcement purposes only.
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and provide useful long-range warning for pilots and ships. In some experiments he was able to detect thunderstorms over Africa, 2,500 kilometres (1,600 mi) away.
524:, so as it travels through the antenna loops, the relative phase that meets each part of the antenna changes. This causes the line to be deflected into an ellipse or
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not longer than 454 milliseconds, too short to be located, or intercepted for decryption, but the system had not become operational by the end of the war.
330:, CH stations were located as far forward as possible, along the shoreline, in order to provide maximum warning time. This meant that the inland areas over the
544:
became simple. Hash marks on either side of the cursor allowed measurement of the width of the display, and use that to determine the amount of blurring.
175:
system, a "field coil". Two such coils, one for each antenna, are arranged close together at right angles. The signals from the two antennas generated a
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received the signal in slightly different locations or angles, and then used the resulting slight differences in the signal to display the bearing on an
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antenna. By taking several such measurements, or using some other form of navigational information to eliminate one of the ambiguous directions, the
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display. This process was essentially instantaneous, allowing it to catch even the shortest signals, such as from the U-boat fleet.
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200:, or signals on the fringe of reception, this was a difficult process. Fix times on the order of one minute were commonly quoted.
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less weight than those that appeared stable and well-defined. Several of these DF groups continued into the 1970s as part of the
203:
Some work on automating the B-T system was carried out just prior to the opening of World War II, especially by French engineers
264:, but in 1924 they decided to return the location for use by other units in the RAF. In July 1924 Watt moved to a new site at
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1008:
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76:, although typically incorporated into a larger suite of radio systems and radars instead of being a stand-alone system.
373:. In simulated battles during 1938 the system was demonstrated to be so useful that the Ministry responded by providing
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The lightning strikes lasted such a short time that traditional RDF systems using loop antennas could not determine the
250:(CRT) could be used as an indicating element instead of mechanical systems, but did not have the ability to test this.
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955:: A paper on the technology and practice of the HF/DF systems used by the Royal Navy against U-boats in World War II
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187:(B-T) was widely used on ships, although rotating loops remained in use on aircraft as they were normally smaller.
598:
466:
843:
999:
deRosa, L. A. (1978). "Direction Finding". In Blyd, J. A.; Harris, D. B.; King, D. D.; et al. (eds.).
73:
982:
Very Special Intelligence: The story of the Admiralty's Operational Intelligence Center in World War II
67:(HF) refers to a radio band that can effectively communicate over long distances; for example, between
17:
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of air control relied on ground direction, some solution to locating their own fighters was needed.
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emits radio signals. The signal is spread across many frequencies but is particularly strong in the
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spectrum, which was one of the primary radio frequencies for long-range naval communications.
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away. These stations would listen for broadcasts from the fighters, compare the angles to
8:
424:, "Huff-Duff" was a valuable part of the Allies' armoury in detecting German U-boats and
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108:
556:– remotely confirming that a superhet radio receiver is listening to a certain frequency
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ships. It is estimated HF/DF contributed to 24% of all U-boats sunk during the war.
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1020:
Secret Weapon: U.S. High-Frequency Direction Finding in the Battle of the Atlantic
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had demonstrated that measurements of these radio signals could be used to track
212:
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599:"The development of a high-frequency cathode-ray direction-finder for naval use"
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fore/aft. The X channel thereby represents either east/west, or port/starboard.
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159:, used for both naval and aerial navigation. The basic concept used a
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The basic concept is also known by several alternate names, including
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397:. The circular indicator provides a direct reading of the relative
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in the space between the coils, which was picked up by a rotating
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HF/DF - Royal Navy High Frequency Radio Direction Finding, WW2
640:[HF/DF (or Huff-Duff): A French Invention] (in French)
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323:
683:
The Secret War [Ep7 2/5]: The Battle of the Atlantic
79:
In earlier RDF systems, the operator mechanically rotated a
942:"HF/DF An Allied Weapon against German U-Boats 1939–1945"
638:"Le HF/DF (ou Huff-Duff) : Une Invention Française"
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initially was unable to supply the numbers requested by
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Britain's Shield: Radar and the Defeat of the Luftwaffe
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from-which signals are received - red numerals for to
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707:
Biographical Dictionary of the History of Technology
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did not have radar coverage, relying instead on the
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296:, which provided easy hook-up and had a persistent
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752:Journal of the Institution of Electrical Engineers
747:"An instantaneous direct-reading radiogoniometer"
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961:"Radio Research at Ditton Park - II: 1922–1927"
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27:Electronic equipment for finding radio sources
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480:From August 1944, Germany was working on the
460:in Fife, Bower in the Scottish Highlands and
211:, working in the French division of the US's
34:FH4 "Huff-duff" equipment on the museum ship
830:"Naval Radio Operations During World War II"
610:"Adcock/Watson-Watt Radio Direction Finding"
784:. Amberley Publishing. p. Chapter 10.
361:The need for DF sets was so acute that the
354:To aid in this process, a system known as "
103:starting in 1926, as a system for locating
390:"Super Duff" equipment on the museum ship
777:
700:
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1018:Williams, Kathleen Broome (1996-10-01).
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958:
729:
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171:to the broadcaster could be determined.
155:was a widely used technique even before
29:
1003:. Los Altos, CA: Peninsula Publishing.
418:intelligence from breaking German codes
14:
1056:
998:
979:
965:Radio Research Organization Newsletter
709:. Taylor & Francis. p. 1280.
701:McNeil, Ian; Day, Lance, eds. (2003).
99:The system was initially developed by
940:Bauer, Arthur O. (27 December 2004).
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47:, usually known by its abbreviation
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805:"High-frequency direction finding"
25:
1090:
1069:World War II American electronics
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959:Gardiner, G. (15 February 1962).
636:Pexee le Vrai (16 October 2006).
487:, which would transmit an entire
1064:World War II British electronics
819:, Cipher Machines and Cryptology
817:"Kurzsignalen on German U-boats"
139:when the antenna is considered.
45:High-frequency direction finding
1074:World War II Allied electronics
836:
822:
809:
798:
771:
745:; Herd, J. F. (February 1926).
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318:During the rush to install the
272:. This site already hosted the
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467:Composite Signals Organisation
218:
13:
1:
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185:Bellini–Tosi direction finder
125:Cathode-Ray Direction Finding
444:" was then encoded with the
274:National Physical Laboratory
223:It had long been known that
7:
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10:
1095:
1001:Electronic Countermeasures
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405:of the ship, green for to
311:
142:
131:DF, and for its inventor,
1022:. Naval Institute Press.
778:Zimmerman, David (2010).
1049:Huff-Duff simulator demo
980:Beesly, Patrick (1978).
765:10.1049/jiee-1.1926.0051
1079:Radio direction finding
153:Radio direction finding
508:
430:Battle of the Atlantic
409:
382:Battle of the Atlantic
57:radio direction finder
41:
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389:
326:systems prior to the
33:
703:"Robert Watson-Watt"
74:signals intelligence
59:(RDF) introduced in
853:: 8–9. 21 May 1976.
371:RAF Fighter Command
253:Watt worked at the
109:RAF Fighter Command
844:"The Evesdroppers"
743:Watson Watt, R. A.
509:
475:Wacław Struszyński
410:
308:Battle of Britain
233:Robert Watson-Watt
137:Adcock/Watson-Watt
101:Robert Watson-Watt
42:
1029:978-1-55750-935-2
1010:978-0-932146-00-7
991:978-0-7221-1539-8
926:, pp. 17–19.
902:, pp. 14–15.
815:Dirk Rijmenants,
562:- "Elephant Cage"
328:Battle of Britain
205:Maurice Deloraine
16:(Redirected from
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182:
178:
172:
170:
164:
162:
158:
154:
140:
138:
134:
130:
126:
121:
119:
114:
110:
106:
102:
97:
95:
91:
86:
82:
77:
75:
70:
66:
62:
58:
54:
50:
46:
40:
39:
32:
19:
1019:
1000:
981:
964:
948:. Retrieved
919:
907:
895:
883:
878:, p. 6.
871:
866:, p. 7.
859:
850:
838:
824:
811:
800:
780:
773:
756:
750:
737:
725:
706:
696:
688:the original
682:
668:, p. 4.
642:. Retrieved
631:
626:, p. 2.
605:
594:
589:, p. 1.
542:
538:
534:
530:
518:
510:
488:
482:
479:
471:
450:
437:Kriegsmarine
434:
411:
393:
378:the battle.
375:Bellini-Tosi
367:Hugh Dowding
363:Air Ministry
360:
353:
344:
317:
302:
290:
286:
282:oscilloscope
252:
241:
222:
202:
189:
173:
165:
161:loop antenna
151:
148:Before HF/DF
136:
132:
128:
124:
122:
98:
94:oscilloscope
81:loop antenna
78:
61:World War II
52:
51:or nickname
48:
44:
43:
37:
560:Wullenweber
499:Description
489:kurzsignale
442:kurzsignale
428:during the
416:("ASDIC"),
412:Along with
348:triangulate
266:Ditton Park
219:Watson-Watt
157:World War I
133:Watson-Watt
1058:Categories
950:2008-01-26
924:Bauer 2004
912:Bauer 2004
900:Bauer 2004
888:Bauer 2004
876:Bauer 2004
864:Bauer 2004
666:Bauer 2004
624:Bauer 2004
587:Bauer 2004
572:References
522:wavelength
462:Goonhavern
458:Anstruther
456:in Essex,
356:pip-squeak
320:Chain Home
314:Pip-squeak
258:Met Office
198:Morse code
193:goniometer
118:Royal Navy
984:. Spere.
566:Y service
407:starboard
392:HMS
294:Bell Labs
262:Aldershot
225:lightning
129:Twin Path
105:lightning
53:huff-duff
36:HMS
18:Huff-duff
851:Time Out
548:See also
454:Ford End
298:phosphor
229:longwave
181:solenoid
127:(CRDF),
90:antennas
85:solenoid
933:Sources
644:18 July
514:heading
399:bearing
394:Belfast
244:bearing
169:bearing
143:History
69:U-boats
38:Belfast
1026:
1007:
988:
788:
713:
485:system
483:Kurier
420:, and
270:Slough
135:DF or
967:(10).
945:(PDF)
847:(PDF)
493:burst
491:in a
422:radar
414:sonar
324:radar
322:(CH)
268:near
255:RAF's
49:HF/DF
1024:ISBN
1005:ISBN
986:ISBN
786:ISBN
711:ISBN
646:2014
435:The
403:port
207:and
761:doi
260:in
83:or
1060::
963:.
849:.
757:64
755:.
749:.
705:.
673:^
654:^
616:^
579:^
469:.
432:.
284:.
63:.
1032:.
1013:.
994:.
953:.
832:.
794:.
767:.
763::
732:.
719:.
648:.
440:"
20:)
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