THE BATTLE OF THE BEAMS PART 1

By D. V. Pritchard, G4G VO, 55 Walker DL,Leigh on Beacon Dijhnen. Light Beacon after dark. Knickebein from Sea, Essex SS9 3QT, England 0600hr on 3159 Shortly afterwards, acooperative prisoner said that Knick- ebein was a beam so narrow and exact that two of them could pinpoint a target with an accuracy of less than a kilometer. He 1940...Now, nearly 50 years from those near-disastrous also added that Knickebein was in some ways similar to X- days, how many of us remember (or even know of) the debt Gergt, assuming that we were familiar with both systems! of gratitude owed to one man who confounded the radio From the wreck of another Heinkel, a diary was rushed to experts and overcame officialdom to earn Churchill's praise Jones. It read: March 5. Two-thirds of flight on leave. Afternoon as the man who "broke the bloody beams" - who went on training on Knickebein, collapsible boats, etc. to unravel the secrets of German radar and Hitler's "V By this time, the cryptographers at had per- weapons," the V1 pilotless flying bomb (the 'tfoodlebug'] and formed a near miracle by breaklng the German Enigma code. the V2 rocket? One of the intercepted messagesfrom a German aircraft was sent to Jones: Knickebein, Kleve, is confirmed at position 53O24' north and lowest. This meant that the aircraft had orn in London in 1911, R. V. Jones was educated at reported receiving the beam a few miles south of Retford in St. Jude's, Herne Hill, and later at the Elementary Nottinghamshire, and Kleve (whel'e Anne of Cleves came BSchool in Sussex Road. Brlxton, where he won a from) was on the nearest German soil to England. scholarship to Alleyn's School, Dulwich. Awarded an Open But, clearly, there had to be two beams: one along which Exhibition in 1929 towadham College, Oxford, he worked in the flew, and another one - amarker beam - to tell the Clarendon Laboratory under Professor Lindmann (later the pilot when he was approaching his target. Evidence of this Lord Cherwell and 's wartime Scientific second beam arrived a few days later in yet more salvaged Adviser), where he turned his talents to infrared detection - papers from a crashed Heinkel. Long-range Radio Beacon: an interest he was to pursue for the next 30 years. Knickebein (Bredstedt) 54O39: 8O57: Knickebein (Kleve) In 1939, he was appointed Scientific Officer to the Military 51°47'5", 6O6: IntelligenceService (MIG) to find out what the Germans were So Bredstedt in Schleswig-Holsteinwas the source of the doing in theway of applying science to warfare. In early 1940, second beam! he came to believe that they had a radio-navigation system by which they hoped to bomb accurately at night. Amateurs and experts Obviously beams less than a kilometer w~deat well over 300 Knickebein-the crooked leg km called for very high frequencies - possibly something in From captured documentsfound in crashed German air- the centimetric region.And although this part of the spectrum craft he came across the word Knickebein, or "crooked leg." was in some use at the time, the power generated by valves The Germans' code names were informative - thisone even then available was very low. Certainly the German system sug- sounded like a beam. But what kind was it? gested they had overcome the problem. (It wasonlylater that Then two prisoners of war were overheard to speak of we discovered that German radar had been operating on 50 something called X-Gerat, or "secret apparatus;" evidently cm since about 1930!) it was something used in an aircraft, and involved radio pulses. However, Rowley Scott-Farnie,G5FI (then a signalsofficer A thriller could hardly havea more intriguing title, but what was in RAF Intelligence), showed Jones a report by T. L. Eckers- X-Geriit- and was it the same as Knickebein? Deeply ley(thecountry'sleading propagationexpert), in which Eck- interested,Jones pressed his Intelligence sources for more ersley had computed the possible range of a20-cm transmit- information and in March was rewarded with the navigator's ter sited in the Hartz Mountains. If the calculations were notes from a shot-down Heinkel. NavigationalAid: Radio Bea- correct, the signals would bend round the earth and might cons working on Beacon Plan 'A"Additionally from 0600hr well be heard by a bomber at 20,000 feet over England. This

Ham Radio/June 7989 29 information, together with the evidence he had already col- tific brains looked askance at the young man who questioned lected, prompted Jones to alert Professor Lindemannto the established wisdom. Then, suddenly, Jones wassummoned possibility that the Germans had a narrow-beam system for to a meeting at Downing Street. bombing the country. Lindemann naturally countered with Thinking the message was one of Scott-Farnie's practical the objection that the frequencies they would have to use jokes, he arrived half an hour late to find the meeting already could not possibly bend round the earth, but Jones produced in progress. A galaxy of talent confronted him. Eckersley'scalculations and told him that indeed they could. Churchill sat on one side of the table flanked by Lindemann But how were the Germansdoing it? Inspection of captured on hisleft and Beaverbrookon his right. Facing them wassir aircraft revealed nothing unusual and the radio equipment Archibald Sinclair (the Air Minister),Sir Cyril Newall (Chief of seemed perfectly normal - certainly nothing in the way of the Air Staff), Sir Henry Tizard, Watson-Watt, and Portal and centimetric receivers. He pressed for yet more information, Dowding (Commanders-in-Chief of Bomber and Fighter especiallyfromthe prisoner-of-warinterrogation centers. Did Commands). Breathing his apologies to the Prime Minister, their aircraft carry special receivers for beam reception? Had Jones took his place at the end of the table. An argument was we missed something? taking place - did the beams exist or didn't they7 Soon Jones Quitecorrectly the prisonersadmitted nothing. But at one realized that nobody in the room knew as much about the mat- center a prisoner was overheard to tell his friend that no mat- ter as he did. Suddenly Churchill snapped a question at him, ter how hard we looked for the equipment we would never find and feeling he couldn't answer it out of context Jones said, it. This startled Jones, for it implied that it was under our very "Would it help, sir, if I told you the story right from the start?" noses and therefore we would never see it. Methodically he Churchill seemed somewhat taken aback but then replied, sifted through the captured equipment, but theonly item that "Well yes, it would." fit the bill was the receiver marked E BI 1 (Empfanger Blind For the next 20 minutes Jones outlined his evidence. As he 1) - Blind Landing Receiver Type 1 - which was used by later recalled I.'. .although Iwas not conscious ofmy calmness both the RAFandthe Luftwaffefor blind landing on the Lorenz at the time, the very gravity of the situation somehow seemed Beam System. to generate the steady nerve for which itcalled. Although Iwas The Lorenz System, however, only had a range of about 8 only28, andeveryone else around the table much my senior km at best, unless the Germans had somehow dramatically in every conventionalwa): the threat of the beams was too seri- increased its range. Knowing that Farnborough had evalu- ous for ourresponse to bespoilt by nervousness on my part." ated the equipment, he inquired if there was anything unusual When he had finished, an air of incredulity filled the room. about the receiver. Sir Henry Tizard demanded to know why the Germans should "No," came the reply. "But since you mention it, the receiver use a beam anyway, assuming such a thing was possible. Our is many times more sensitive than they would ever need for own pilots found their targets very well by astro-navigation. blind landing." (They didn't! Author:) Others round the table seemed doubt- Could that be it! Dr. Jonesspoke to Lindemann, whodrafted ful. But Churchill was convinced and asked Jones what a note to Churchill. He wrote: '7hereseems some reason to should be done. suppose that the Germans have some type of radio device '9 told him that the first thing was to confirm their existence with which they hope to find their targets." by discoveringand flying along the beams for ourselves, and Churchill initialed the note and sent it to the Air Minister, that we coulddevelop a variety of countermeasuresranging adding: '7hisseems most intriguing and Ihope you will have from putting a false cross-beam for making the Germans drop it thoroughly examined." their bombs early, to using forms of jamming ranging from Acommitteeof inquiry was formed and Squadron Leader crude to subtle." R. S. Blucke was put in charge of flying operations. Three With a typical "Let this be done at once!" Churchill then Ansons were fitted with suitable receiversandflown by Lorenz- turned round and tore astrip off the fortheir tardi- trained ~ilots.Rowlev, GSFI, told JonesthattheGerman pre- ness. set freq"encies were likely to be 30,31.5, and 33.3 MHz, and sure enough afew days later a scrap of paper recovered from And expert amateurs yet another crashed aircraft read: Knickebein (Kleve) 31.5. Elated at having convinced the Prime Minister, Jones On June 20 a Heinkel was shot down. The radio operator dashed away to attend a conference in the off ice of the Direc- had bailed out, had torn his notes into shreds, and wasactu- tor of Signals, Air Commodore Nutting, to discuss the possi- ally burying them when he was captured. An Intelligence bility that the Germans might exploit pulse techniques as NCO unearthed them, gummed them together, and sent nagivational aids. T L. Eckersley was to give evidence. How- them to London: VHE Knicke 54°38171'N, 8O56'8" E, ever, because Eckersley disagreed with Jones'sfindings, the 51°0'30"N, Eqms., Stollberg30mc/s. Kleve 51°47'N, 6O2/E, subject reverted to Knickebein. 55ON, 2OEqms., 31.5 mc/s. But what about those propagation calculations?Oh, those! Thisseemed toconfirm the existence of another Knickebein Eckersley pooh-poohedthem; he didn't believe them himself. installation at Stollberg and in Schleswig-Holstein.It also con- He was only trying to demonstrate how far the signals might firmed Scott-Farnie'sguesses about the frequencies.Yet after go under certain conditions. He thought he had been stretch- two flights the Ansons failed to find the beams. ing theorytoofar, and doubted if signals in the30-MHz band Was Jones wrong after all? Many thought so. Sir Henry Tiz- would curve round the earth. ard was skeptical (and fell from Churchill's favor as a result), The Ansons had fa~ledto detect the beams during their Air Chief Marshal Dowding was doubtful, and Air Chief Mar- previous flights and another one was due that evening. In shal "Bomber" Harris was scathing. Other military and scien- order to cancel it the Principal Deputy-Director of Signals,

30 Ham Radio/June 1989 DRIVEN REFLECTOR1 ELEMENT REFLECTOR 2 DASH ZONE

CAM- SWITCH ANTENNA (MOTOR DRIVEN) FEED

I I The principle of the operating reflecton. -- -- - The principle of the Lorenz beam system. Captain 0.G. Lywood, picked up the phone saying, "Well, we have here the greatest expert on radio propagation in the country and he says the beam theory is all wrong. We've wasted a lot of time and let's not waste any more. This even- ON THE EOUISIGNAL. DOTS ing's flight should be canceled!" But Dr. Jones stood his EXACTLY FILL THE GAPS BETWEEN THE DASHES. SO ground. Pointing out that Eckersley's evidence had neutral- THAT THE PILOT HEARS A ized itself because he had said one thing afew months before CONTINUOUS NOTE- and now said something quite different, and that enough evi- EOUISIGNAL I dence already existed to convince him, he demanded that Eckersley'sstatement should be ignored. He also told Lywood that if the flight wascancelled he would "jolly well let the Prime Minister know who had countermandedhis orders." Lywood backed down. From the Chair, Air Commodore Nutting demanded: "And what do wedo if we find the beams?" Quietly Jones whispered to Rowley Scott-Farnie, "Go out and get tight!" Black night and bright dawn Dr. Jones went home to spend one of the most miserable nights of his life. "Had I,afterall, made a foolofmyselfandmis- behavedso spectacularly in front of the Prime Minister? Had ljumpedto false conclusions? HadI fallen fora great hoax by the Germans?Aboveall, had Iarrogantly wasted an hour of the Prime Minister5 time when Britain was about to be invaded or obliterated from the air?" It wasa beautiful summer's night - the shortest night of a TRANSMITTER SWITCHED FROM terrible year for Britain -when Flight-LieutenantBufton and DASH ANTENNA TO DOT ANTENNA Corporal Mackie climbed aboard their Anson and flew over the area between Huntingdon and Lincoln. Neither had been told the Knickebeinstory, but merely to search for beams with Lorenz characteristics. Suddenly on the Hallicrafters receiver The principle of the Lorenz (Knickebein) beam. they heard signals on 31.5 MHz. Dots! The aircraft swung to the north. Still dots. Then a continu- having dots to the south anddashes to the north, on a bear- ous note, and later, as expected, azone of dashes. When the ing of 104O(284OT). dashes ceased, Bufton and Mackie began intently to plot the 2. The carrier frequency of the transmissions on the night of beam. The following afternoon Bufton's report wason Jones's 21/22 June was 31.5 mc/s, modulatedat 1150 cycles andsimi- desk: lar to Lorenz characteristics. I. There is a narrow beam (approximately 400 to 500 yards 3. There is a second beam having similar characteristicsbut wide) passing through a position 1 mile south of Spalding, with dots to the north and dashes to the south synchronized

Ham Radio/June 1989 33 The Lorenz System In 1932, Dr. E. Kramar of the German Lorenz Company FROM RECEIVER began to develop a high-frequency blind landing system on pre-set frequencies between 30 and 33.5 MHz, continu- MODULATION ous wave modulated at 1150 Hz. The beacon transmitter NOTE TO INSTRUMENTS and its associated antenna system stood at the end of a runway and had a range of 3 to 5 km (sometimes more A) depending on conditions) even though the transmitter developed 500 watts. The output was fed to a single dipole, to the left and right of which and at a quarter-wave spacing 1/10 was a single reflector cut at its center point. A relay was PRE-APPROACH lNDlCATlON used to alternately close and open the reflector, as shown , 7-9m l7OOHz) in Figure 1, whereupon a beam was generated at an angle left and right of the driven element composed of dots to 1/15+ $i I a FINE-APPROACH INOICATION one side and dashes to the other (see Figure 2). These ah~lnmI 7-9m 11100Hz) alternating beams partially overlapped each other centrally I to give a narrow zone of about 3O angle in which the dots and dashes were heard as a single note, telling the pilot he was on the correct approach (see Figure 3 and 4). A EOUlSlGNAL PORT simple presentation unit was also provided in the cockpit rrc -! 9m lll5OHz) which showed the course deviation on a meter; a form of B) range measurement was furnished by an S-meter arrange- ment. Two additional transmitters were employed to aid landing (Figure 5). At a point 3 km before the runway was an early- approach system on 38 MHz with a power of 5 watts, but hav- ing aslower-keyingrate and alower modulation note. The sec- ond system was comprised of a transmitter at 300 meters before the runway, with a higher key rate and modulationtone. py F-----ur ~1 UUJUUWUU~p~ Both these systems operated a lamp on the presentation unit b @////////&kllA to give further visual indication. Ip-1/8 1 i : : 11 II I I #I I, : ; The accompanying aircraft receiver was known as the EB I I-7/8+ ; ; I I 1 (Blind Landing Receiver I),which wasdevelopedfrom the Li- +ii+i; +k;: , i$ -,b I- I- earlier EBE receiver. The system was made available to Lufthansain 1934 and theaircraft were fitted with vertical rod antennas, usually quarter-wave whips. Later, the produced a specificationfor what was to be called the Blind Landing System FuB 1, and which required two separate @a@L r/R LR receivers - the EB 1 for signals in the range 30 to33.3 MHz, DOT- ZONE APPROACHING THE OASH- ZONE and the EBL2for38 MHz. All multi-enginedaircraft of the Luft- C) EOUISIGNA L waffe were fitted with these up to 1941. As war seemed inevitable,Dr. Lohmann of Telefunken devel- The target approach indication with the Knickebein system. (A) oped a much larger system which was called 721 in Pulse rectifying circuit. (8) Pulse rate timing - distances in meters, 1938. This was an antenna array of metal girders 30 meters tones in hertz (for approach on flightpath). (C) Pulse rectification meters long which revolved On a circular and waveforms, tone-modulated signal. At rectifying circuit and as high and final pulse. track. In the middle was a 50-watt transmitter for 30 to 33.3 MHz. The framework supported 16 vertical wire dipoles and with thesouthern beam, apparentlypassing through apoint reflectors and was arranged as an angle of 165' (looking near Beeston on a bearing lying between 60°+ andless than down on the array), so that eight two-element antennas were 1049 in each leg of the framework. From this "broken neck" appear- In other wordsthe director beam wasaimed at where ance, geknickten in German, came the Knicke- the Rolls Royce factory produced engines for the RAF - as bein. Jones had suspected. The impact of Bufton's report on the Details of the transmitters and receivers used are, unfor- meeting thatafternoon may well be imagined. Jubilation was tunately, no longer in existence. However, the antenna lobes intheair. Even "Daddy" Nuttingwasskipping roundthe room were similar to those shown in Figure 6, except that the nar- in delight. All doubts were now drspelled and countermeas- row equisignal zone was +0.3O wide and the key~ngof the ures could go ahead urgently. dashldot system had a ratio of 1:7. The improved receiver, In the midst of the revelry Scott-Farnie buttonholed Jones: another mark of the EB 1 known as the Fu BI 1, could receive "Remember what you said yesterday?" the beam at a range of 500 km and a height of 6500 meters. So they bowled across to a pub to celebrate. The principle was that the main beam was directed at a tar-

34 Ham Rad~o/June1989 - _-----

DASH ZONE \ \

DOT ZONE ......

MAIN FORE-APPROACH BEACON 38MHz. SLOWER KEYING RATE

- pp - - The prfnciple of the Lorenz blind landing system. get, and the pilot knew he wason course when acontinuous Pulling the Crooked Leg note appeared in the receiver. If he strayed to the left, a prepon- derance of dots was heard; a swerve to the right produced A special unit was set up to counter the beams(which were dashes. code named Headaches) under the command of Wing Com- By 1940,ten smaller versionsof Knickebein had been built mander E. B. Addison of No. 80 Wing at Radlett. The techni- which required only acircular trackof 45 meters in diameter. cal design of the countermeasures was the responsibility of Each leg of the angled frame contained only four sets of ver- Dr. Robert Cockburn of the Telecommunications Research tical two-element arrays, which were broadbanded to tune Establishment at Worth Matravers. Both organizations were between 30 and 33.3 MHz by construction from wide- accorded the highest priority. diameter tubing. The range wasalmost the same in practice Receivers were placed on top of the masts of certain sta- as the large Knickebe~n,although the main beam w~dthwas tions of the RDF (radar) system, and the unlucky wider at k0.69 operators in these dizzy crow's-nestswere connected by tel- As already mentioned, when in use the main beam was ephone with Fighter Command HeadquartersatBentley Pri- directed at the target, and at a predetermined point some dis- ory. tance before the target was reached it was overlapped by a Professor Jones records how he, too, spent a night on top second beam on a different frequency. This told the pilot his of one of these towers - listening to the signals which Eck- distance in kilometers from hisobjective. Figure 6 shows the ersley had said could not be heard even by a bomber at method in more detail. 20,000feet over England. 'When about dusk the German Although no details remain of the receivers used, it is known beams wereswitched on, the men in the towers would be able that they were t.r.f types and, as will be seen later, very suscep- to pick them up and let us know for instance, if a beam was tible to jamming. For this reason a Dr. W. Kloepfer of Lorenz going between tower ;4' and tower 'B.' That would give us a developedasuperhet,the EBL3 H, which neededonly slight clue to the beam's position, and one of our chaps would go preparation as it used the same p.s.u. as its predecessor and up in an Anson and fly back and forth until he picked up the fitted the same cabinet. This was tunable over a number of beam, which could then be plotted." channels from 1 to 34 in the spectrum 30 to 33.3 MHz, and The first jammers were diathermy sets used by hospitals to could receive the Knickebein transmissions at the same cauterize wounds. These were requisitioned and tuned to the height and range as the earlier model. Knickebein frequencies. Although they only emitted a mush

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The antenna pattern of the Knickebein array. of signals, it was thought that they had some effect on the beams. Installed mainly in police stations, they were switched on when ordered by No. 80 Wing. Fortunately we had acquired the Lorenz license before the war, so Lorenz transmitters were modified and strategically placed, as were "Meacons," or mock beacons.The Luftwaffe, with more than 80 radio beaconsattheir disposal in Germany 1.2M-1.5M PARABOLIC DISHIFEEDIDOWN CONVERTER to 2 Meters and occupied Europe, began to find an ever- RCP. LCP. or Llnear Polarization .LNA- NF. 1.5dB. G--22dB ~ncreasingproblem. But it was Cockburn's jammers (code Preselector Flller - named Aspirins) that were most effective. Immensely power- ! Machlned 4-Pole Combllne ful, they flooded the beams with dashes and the German I p M~crostrlpMlxer on hlgh dlelectnc alumlna pilots, flying into their own dash zones, would steer tof~ndthe Local Osc~llator- Heater equisignal only to find Cockburn's dashes. They would con- Stablllzed. - Pppm lor CW/SSB .Down Converter mounted in feed tinue turning until they found a dot zone (and Cockburn's assembly lor optimum dashes), which often synchronized into a false equisignal ! performance note. After they found themselvesflying round in circles dur- Frequmes available: 1.296-1.691 GOES WX- 2.304-2.40 OSCAR Mode-S -3.456GHz ing bombing raids for a few weeks, they came to realize that rn FeedIDownConverter Assemblies are interchangeable In common feed mount. we had found and jammed their system. We had, in fact, 1.2 Meter or 1.5 Meter Spun Aluminum Dish has mlg, hardware for 1.5" mast "pulled the crooked leg." An additional bonus lay in the fact Feed Antenna has + MBiC Gain, selectable polar~zatlon. that it was several months before the German pilots had the PRODUCT PRICE LIST courage to tell Goering that Knickebein was useless. RCP'LCP Feed Assembly.Type N connectors. Model WCFA-(lreq) ...... $185.00 Had the system worked successfully, a number of Linear Polar~zedFeed Assembly.Type N Conn. Model WLFA-(lreq) ...... 135.00 (Specrfy frequency: 7.296. 1.691. 2 304.2.400. 3 456GHz) could have put bombsevery 17meters into a selected target. 1.2 Meter Spun Aluminum Dlsh with mtg. hardware WUDA-1.2M ...... 295.00 As it was, our citiessufferedsevere mauling from the Luftwaffe. 1.5 Meterspun Aiumlnum Dfshwlth mtg. hardware WUDA-I .5M ...... 395.00 LNA- 2 stage GaAsFET, NF. 1.ME. G -22dB. SMA Conn WLNA-(freq) ... 265.00 Who knows how much worse the loss of life and property (Speaty lrsquency~1.2. 1.69 2 35. 3 456GHz) would have been but for the efforts of a young physicist who Preselector Bandpass F~lter.Machlned 4-Pole Combllne. SMA conn. (Specrfy Irequency: 1.296. 1.697.2 3. 2.4. 3 456GHz) refused to believe theexperts, and courageously challenged Model WMCF-(freq) 85.00 his superiors. Microstrip Mixer-Thick F~lm.Machined Hous~ngWHMM-(treq) ...... 45.00 Today one wonders how many Londoners and citizens of Local Oscillator - Heater Stabillzed.Thlck Fllm.WHL0-(lreq) ...... 325.00 (Specify frequency: 1.151. 1.5535, 2.159.2.255. 3 311. oranyspot FoI our other major cities have heard of Professor R. V. Jones. Q Complete FeedDown Converter to 2 Melen. Model WFDC-(lreq) ...... 675.00 (Specrfy frequency: feed type) (Olher IF3 avarl.. GOES- 137.5MHz) Complete DishrFeed!Down Converter Assembly 1.2 Meter Dish. Model WDDC-I .2-(lreq) ...... 955.00 1.5 Meter Dlsh. Model WDDC-1.5-(freq) ...... 1055.00

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By D. V. Pritchard, G4GV0, 55 Walker DL, Leigh antenna array mounted on a platform which could rotate on Sea, Essex SS9 3Q7; England through 3609 The antennas were mounted on a gantry and spaced at 14.75 meters (3.5 wavelengths). Originally, sim- ple half-wave dipoles were employed, but before long direc- tors and reflectors were added for extra power and range; these were energized with pulses at 120 per minute via a vacuum switch (soon replaced by a capacitor, nicknamed s early as 1934, when Knickebein was in its infancy, a "mill switch," designed by Dr. K. H. Fischer). The a German scientist began to have doubts about schematic block diagram of this system is shown in Figure ,its efficiency if exposed to jamming. He was Staats- 1. A half-wave Lecher line is used in conjunction with the rat (Privy Councillor) Dr. H. Plendl of the Deutsche Ver- "capacity" switch and its associated inductances to pulse suchanstalt fijr Luftfahrt (German Aeronautical Research both dipoles with the required dotldash sequence. Establishment) and he began to produce designs for a new The array generated a fan of 14 beams each with a band- system for accurate blind bombing. width of 0.05O (Figure 2), and eight of these installations Under his leadership, a new department was formed at were erected in Germany, followed by many more on the Rechlin (the German equivalent of Farnborough) which coasts of occupied Europe. By now the airborne equipment began research in June of that year. This was in coopera- had also been drastically improved by Dr. H. Hanel and tion with another department led by a Dr. W. Kijhnold which Dr. Rijcklin Telefunken, who had designed and developed was also engaged on beam techniques for blind landing. a superhet for 66 to 77 MHz (code named Anna), while The beams of KUhnold's system, however, had an aperture an analyzing system designed by Dr. Plendl known as the angle of about 59 corresponding to an 8-km beamwidth AVP (Anzeige-Verfahran von Plendl) was being mass- at a range of 100 km, and were clearly unsuitable for produced by Siemens. accurate pinpointing of targets. Obviously a beam width At the same time a Dr. K. Miiller set up a Mobile Research of not more than O.1° was required and this (at that time) Unit which produced some versatile mobile stations under could be attained with reasonable antenna dimensions and the code name Miibelwagen or "furniture vans." He was suitable power only if a frequency between 66 and 77 MHz also responsible for the clever camouflaging of their were employed. Accordingly, experiments were begun with antenna - a feature which was later to prove troublesome an 80-watt transmitter designed by a Dr. Ochmann which for British counterattacks. was code named Bertha I; as this was not powerful enough The complete system was known as Wotan 1. a second was designed, Bertha 2, which delivered 500 Principle of operation watts and was tunable over the required range. Preliminary tests carried out over Lake Mijritz near Meck- One of the 14 beams was selected to act as a director lenburg in 1935 resulted in ranges of only 1500 meters. Sta- beam which, on being aimed towards the target, provided tionary beam antennas which could be phased to swing a flight path for the aircraft; this system was similar to Knick- through about 10' were used, and the airborne equipment ebein in that the pilot could plot his course according to consisted of two t.r.f. receivers developed at Rechlin and a direction-indicating meter which told him if he was to the an analyzer for unlocking the 2000-Hz modulated dotidash right or left of the beam. The official German layout of the system of the adopted and improved Knickebe~nappara- beam-approach system and its associated cross-beams at tus. Unfortunately, full details of both transmitter and points before the target is shown in Figure 3. Figure 4 receivers are no longer available. represents not only the director beam and reserve beam, but also the cross-beams and the associated fans of beams Wotan 1 which enabled stray aircraft to plot their courses to the cor- By 1938, the system had been greatly improved. Dr. KGh- rect one. The main beams of the system used for the nold had developed ground installations capable of easy devastating raid on in 1940 are shown in Figure dismantling and removal, with an operating cabin and 5, and Figure 6 is another official German layout showing

20 Ham Rad/o/August 1989 DIPOLES

CAPACITY SWITCH w I MOTOR I

Block diagram of X-Geriit feed system and capacity switch for pulsing.

E C

I3

Antenna pattern of X-Gerat system. the disposition of all beam systems in use at that time. (In this series the author has concentrated only on the more FLIGHT PATH ON DIRECTOR BEAM T1 OR TZ widely known systems.) T3 = RESERVE BEAM In practice the bombers did not fly along the director beam immediately after takeoff, but used either normal navigational methods or one of the fan beams, in order to present a smaller target for British radar and to try to cause confusion. The director beam was usually joined sometime after crossing the English coast. At approximately 30 km before the target, the aircraft Official German layout of the X-Gerait system. would encounter the coarse advanced cross-beam which, like the other beams, was similarly pulsed with dots and point, the bomber's radio operator would have consulted dashes - but on a different frequency. Before reaching this a table giving the characteristics of his particular type of

Ham RadiolAugust 1989 21 FINE X-BEAMS AS SET FOR COVENTRY 14/15 NOVEMBER 1940

DIRECTOR BEAM

0 50 100 I50 200 German layout of beams showing main beams and associated fans. -KILOMETRES machine and fed them into a combined calculator and stop- watch called the X-Uhr, or "X-Clock." This was an incredi- bly accurate mechanism designed at Rechlin by a Dr. Hep- The X-Geriit system for Kampf-Gruppe 100. per. A small upper dial on the left-hand side showed how long the instrument had been running, while the lower dial The airborne equipment was installed in the radio oper- was used for calculating the "flight-path ratios." Information ator's position, and repeaters for the course meters were about the aircraft's type, height, and speed was inserted fitted in the cockpit for the pilot's benefit. A motor genera- to give a flight-path ratio of, say, 2.78:1 for 18 km or 3:1 for tor fed from the aircraft's batteries (rotary converter) was 6 km, according to circumstances. placed at the bottom of the installation. Immediately above On arriving in the dash zone of the advanced cross- it were two audio units, to the left of which was the power beam, the operator would listen for the (very brief) continu- distribution panel. The twin receivers for the director and ous note produced by the merging of dots and dashes, and cross-beams were above that and the Anna receiver was press the clock's top button. This started the green "min- on the right. ute" hand and the black sweep hand simultaneously and, according to the inserted data, the time taken for the bombs Intelligence breakthrough to drop was now fed in. The phone shatterd Dr. I?.V. Jones's sleep in the early At the "fore-cross signal" a button on the left was pressed, hours of a morning during the first week of September 1940. whereupon the green and black hands stopped and the "We've got something new here! God knows what it is, red "hour" hand started. When the third button at the main but I'm sure it's something for you!" cross-beam was pressed, the red hand would stop at the The excited voice of Professor Frederick "Bimbo" Nor- same point as the previous ones and, if the correct data man, a cryptographer at Bletchley Park, shook Jones into had been given, the bombs would be automatically consciousness. They had broken some new Enigma traffic released. in which radio beams were mentioned, including the infor- After tests by a research squadron, the system was finally mation that the beam width was 8 to 10 seconds of arc, installed in Ju 52s and He Ills of Kampf-Gruppe 100 - or an angle of 1:20,000, suggesting that the beam was no a group led by an outstanding Luftwaffe officer, Major Vik- wider than about 20 meters at 320 km! tor von Lossberg. Quarter-wave whips were mounted on Then came the electrifying word X-Gerat! Whatever X- top of the fuselage behind the cockpit and these, in con- Gerat was, it was being installed in aircraft of Kampf-Gruppe junction with the whip antenna for RT operation which was 100, one of the Luftwaffe's crack squadrons. situated farther back, gave rise to the nickname "Three- Jones hustled the intelligence services into greater master." activity. Across the Channel the Resistance organizations

Ham Radio/August 1989 23 o E .ELEKTRA 0 S*

+ X = WOTAN I x r. WOTANII * Z .ZYKLOP

Official German layout showing the disposition of all beam systems in use at that time. pulled out all the stops, and British Signals Intelligence Rhein, Elbe, Isal; and Oder. Evidently Kampf-Gruppe 100 (including Voluntary Interceptors - a body of dedicated was working through a book of numbered targets, and by Radio Amateurs) doubled their efforts. Their activities the time the stations were identified Jones had the actual prompted Jones to record h~sappreciation: "Our commu- directions for the beams - and even that the Germans had nity of Radio Amateurs in Britain was to prove an invalua- specified them to the nearest 5 seconds of arc, an accuracy ble reserve, both in Signals Intelligence and Signals propel; of about 10 meters at 320 km! (See Figure 7). as well as furnishing many of the staff for our rapidly increas- But how could such an accuracy be possible on 70 MHz7 ing number of radar stations." It was that well-known Amateur of his day, Rowley Scott- The "Anna" numbers Farnie, G5GI, then an officer in RAF signals lntelligence Further decoded German transmissions revealed the and a close friend of Jones, who reported beam signals existence of coarse and fine beams, Including a mention from the Calais and Cherbourg areas around 70 MHz. By of centimeters. This latter, however, referred to the precision September 24, six beam stations were identified: two north- with which a monitoring vehicle had to be positioned to west of Cherbourg, three near Calais, and the last near orientate the director beam. Frequent mention of something Brest. The Germans had code named them Wesel; Spree, called "Anna" was made, usually associated with a num-

Ham RadiolAugust 1989 25 55, 60, 75, and 85. Another set of numbers gave crystal frequencies (typically 8750 kHz, since 8750 kHz x 8 = 70 MHz) and he suspected that Anna referred to the dial on the aircraft receiver, if not the aircraft itself. Since one set of numbers ended in 0 or 5, and the other in 0 or 0.5, simple deduction showed that the Anna reading had to be divided by 10 and either added to, or subtracted from, a constant number. Learning from the Enigma traffic that a certaln Feldwe- be1 Schumann at a beam station at den Helder had signed a return for 3 crystals for 69.5, 70, and 71.1 MHz and that his station was ordered to transmit on Anna numbers 30 and 35, it was clear that the constant had to be 66.5 if one- tenth of the Anna number had to be added, or 73 ~f it had to be subtracted. As he knew that crystals for 75 MHz existed, the second possibility could be dismissed; when he obtained further confirmation from the two crystals whose frequencies were not exact or half integers, the prob- lem was solved. Other information that emerged from the Anna numbers was that both the coarse and fine beams lay between 66.5 and 75 MHz. Measurement inaccuracy The immense value of Anna numbers was that if the trans- mitted orders to the beam stations could be decoded in time, he could then tell 80 Wing the frequencies to be jammed. Incredibly, his interpretation of the numbers was Beam patterns of mobile X-Gerat. rejected because our monitoring services thought there out where they were. However, Jones silenced these critics were frequencies outside the range he had found. Dr. by pointing out that there was no evidence that Kampf- Jones's hackles rose - a posture they were seldom slow Gruppe 100 was upset by our countermeasures (which was in assuming - and plain words were spoken. "These, it true) and were not only using the system, but acting as path- transpired, were due to bad measurement of the frequen- finders for other Luftwaffe groups. cies of the German beams on the part of the countermeas- Yet other problems had to be overcome. ures organization, a feature that was to plague us through If the Enigma transmissions to the beam stations (usually the whole battle. The fault in this case probably lay not with sent out in the afternoon preceding a raid) could be bro- the observers, but with the calibration of our receivers which ken in time, we would know where and when Kampf- were not up to the German standard of precision." His find- Gruppe 100 was going to attack, and our fighters could ings were accepted. be ready for them. Our jammers, too, could be set on the Dr. Robert Cockburn of the Telecommunications correct frequencies. For this to be possible the cryp- Research Establishment, having successfully prescribed tographers at Bletchley Park strained all their resources - "Aspirins" for the Knickebein "Headaches," now developed and it was a magnificent effort, for they achieved this incredi- "Bromides" for this new system which was code named ble feat late in October. Dr. Jones was then able to tell "Ruffian." We now knew that the director beam was radi- Fighter Command the exact place of the attack, the time ated from near Cherbourg and the cross-beams from the of the first bomb to within 10 minutes, the exact speed of Calais area. As insurance against the failure of the main the bombers, their line of approach to within 90 meters, and director beam (Weser), a reserve beam was provided by their height to within two or three hundred meters! the adjacent station (Spree). The accuracy of the beams Yet our night fighters repeatedly failed to find the enemy. was so great that in calculating their paths it was neces- Jones wrote: "Ialmost began to wonder whether the only sary to take into account that the earth is not a sphere, but use the Duty Air Commodore made of my telephone calls flattened towards the poles; this made a difference of 275 was to take a bet with the rest of the Command as to where meters in where a beam from Cherbourg would cross Lon- the target would be for that night." On top of this was the don! growing suspicion that our jamming was not working. Why not? Countermeasures and counter arguments The answer soon came, but not before tragedy struck. Cockburn's jammers came into operation in October, but at this time Kampf-Gruppe 100 began to drop flares over Moonlight Sonata its targets. This was hailed by some of Jones's antagonists On November 10 Jones received an Enigma decrypt of as proof that the beams didn't work, or that the Germans a transmission to the beam stations which told them to pre- were so unsure of them that they were using flares to find pare operations against target numbers 51, 52, and 53, giv-

26 Ham RadiolAugust 7989 ing the beam settings at the same time. It took only a few found it set to 2000 Hz. But our jammers had been modu- minutes to work out that 51 was , 52 was lated at 1500 Hz, which meant that while our carrier fre- , and 53 was Coventry. Then another signal quencies were correct the modulation tone had no effect was passed to him which contained orders for a major oper- on the beams. ation under the code name Moonlight Sonata. Four target "It was one of those instances, of which 1have since found areas were mentioned but there was no indication of the many, where enormous trouble is taken to get the difficult order of the attacks. Frantic guesses were made by the Air parts right and then a slip-up occurs because of lack of Staff and the best they could come up with was that Moon- attention to a seemingly trivial detail. Of all the measure- light Sonata might mean a target in southern England. ments in connection with the German beams, easily the sim- Strangely, no attack had been made on Wolverhampton, plest to determine was the modulation note, because this and on November 14 everyone braced themselves for the could be done at any time in comfort; and yet whoever had coming night and whatever Moonlight Sonata might mean. done it had either been tone deaf or completely careless, Tragically, it was one of those afternoons when Bletchley and no one had ever thought of checking his measure- Park failed to break the Enigma signals in time, and 80 Wing ments. Iwas so indignant that Isaid whoever had made asked Jones which frequencies they should set their jam- such a mistake ought to have been shot." It is hard to believe mers on, giving a list of frequencies as determined by our that the citizens of Coventry would have disagreed with this monitoring aircraft. "I could see at once that the measure- opinion. ments must be wrong, in that they did not match up with Jones's anger was further increased by the fobbing-off the figures Iknew from the Anna code. Itherefore made he encountered. He was told that the modulation note was a mental correction of the measurements as far as 1could. originally 1500 Hz but the Germans had changed their filters For example, 68.6 should have been 68.5, ~four receivers to avoid jamming. This ridiculous excuse was countered by had been properly calibrated, or 70.9 should have been Jones who pointed out that if that had been the case we 71.0. But deciding what, for example, 66.8 meant was more would obviously have heard the change in note for our- of a lottery. The only other clue that Ispotted was that there selves. In any event he was able to prove that Kampf- seemed to be a convention that the director beams would Gruppe 100 had been using the same filters since the start generally be on frequencies between 66.5 and 71.5 and of their operations. the cross-beams between 71.5 and 75 MHz - the On his insistence the jamming modulation frequency was being presumably due to operational convenience. changed and when the Germans later attacked Birming- Remembering that we needed to knock out the main and ham their bombs fell wide of the target, most of them out- reserve director beams and at least one of the cross-beams, side the city. Gradually they came to realize we had bro- Ithen made my mental gamble and suggested a set of fre- ken X-Gergt and their confidence in the system diminished, quencies to Addison which he said he would adopt. All this and Britain which knew nothing about Dr. Jones and his took no more than five minutes on the telephone, but Iwas scientific war went on with "business as usual."[rm well aware that in these snap decisions Iwas probably gam- Reprinted w~thpermlsslon from Pract~calW~reless, PW Publ~shlngLtd., bling with hundreds of lives. Sobering though this thought February 1988. Ed. was, the fact remained that someone had to do it, and I was easily in the best position." Then on the night of November 14th Coventry was attacked, with heavy civilian casualties. What had gone wrong? The next day the decoded Enigma signals to the HAM RADIO beams stations arrived and Jones's wretchedness turned LOG BOOKS to bewilderment. He had guessed the frequencies correctly back by popular demand! - so where was the failure? Room for over 21 00QSO-that's over Incompetence and carelessness twice as many as theother log books The failure arose originally from a silly interservice squab- For contesters, each page contains 30 : st.t,ar QSO's for easy counts. You also get ble which led on to a ghastly mistake. On November 6 one : lopk4 numar : I- to the latest up-to-datefrequency spec- of Kampf-Gruppe 100's Heinkels became lost over south- trumchart. ITU callsign list and ARRL ern England and ditched on Chesil Beach. The Army took DXCC 1st. Spiral bound to lay flat on over, secured a rope around the fuselage and set about your desk. Unquestionably the best salvaging it, when a naval inshore vessel arrived and GREAT log book value around a 1988- demanded to know what the Army thought it was doing. HR-LB...... Spiralbound $2.95 As the aircraft was in the water, salvage was a Navy matter, and taking the rope aboard they dragged the aircraft GIFT klR-3L8 Special BUY3 deeper into the sea, breaking the rope in the process. The Save 22%...... Get 3 $6.95 X-Gerat equipment aboard, now heavy with silt and corro- IDEA Please add $3.75 for sion, was fortunately discovered and rushed to 80 Wing and 8hippIng and handling. then on to Farnborough for investigation. @ @m On November 21 Jones, accompanied by Scott-Farnie and their assistants, went to see it for themsleves. They HAM learned that Farnborough had examined the audio filter and RAM0 BOOKSrORE GREENVILLE. NH 03048 (603) 878-1441

Ham Radio/August 7989 29 THE BATTLE OF THE BEAMS PART 3

Ever since 1939, Dc Plendl of the German Aeronautical Different ideas Research Establishment entertaineddoubts about the effec- In fact several systems were tried for the early Y-System, tiveness of X-Gerat in the face of strong jamming; accord- but the one chiefly employed was the "Y-Range Measuring ingly, schemes for a new system were put in hand at that System Mechanical" developed by Dr. H. J. Schmidtmann time. D. V. Pritchard Dip Ed, G4GV0, concludes this most at Rechlin and Dr. Jenns of Siemens (see Figure 1). Two interesting story tone frequencies of 300 Hz (corresponding to 500 km, the "coarse measuring range") and 3000 Hz (equaling 50 km, the "fine tuning range") were transmitted. Rectifiers loosely By 0..VI Pritchard, G4GV0, 55 Walker DL, Leigh coupled to the transmitting antennas fed both frequencies on Sea, Essex SS9 3QT; England via separate filters and phase converters to two small c.r.t.s, which were also fed the filtered frequencies from the receiver tuned to the aircraft's return signal. Tuning the phase converter resulted in diagonal strokes appearing on the screens which served as null-point indicators; range was read from a scale marked in kilometers. deally, such a system would have only one director Siemens also produced a range measurement known as beam for the guidance of the bomber, and another for the Electrical Notebook, which recorded the ultimate range Ia range measurement system which would enable of five simultaneously measured aircraft. This incorporated ground control to drop the bombs accurately. Clearly a fine-measuring system devised by a Dr. Bekker that used improved accuracy would be needed, and it was possible a larger c.r.t. with a circular range scale showing a range that owing to the nature of the system the number of air- from 0 to 20 km. A transmitted tone of 7500 Hz generated craft on the beam at any one time would be necessarily low. a "dark pulse" circular time zone calibrated against a fur- ther circular "bright zone." The phase-converted voltage Early experiments from the receiver was then transformed into a pulse which Since the only aircraft receiver available was the FuG 17 the electron beam converted into light points, so that a (42 to 48 MHz), a multibeam beacon was designed for it change in range could be observed directly. This system by a Dr. Herzog of the Gotz Company and given the code was somewhat unreliable in that a 5-km variation in range name Wotan 2. A system similar to X-Gerdt was also built was sometimes observed, but nevertheless it was of some which used the Bertha I/-2 television transmitter, with simi- help when enemy jamming was strong. lar pulsing and modulation having a doUdash ratio of 1:7 Later; Dr. Bekker introduced another device known as the modulated at 2000 Hz. Plendl's analyzer was also "Y-System Measuring Electrical" which was produced by employed; this system was envisaged as the director beam the Graetz Company. A modulation note of 300 Hz corres- for the aircraft's flight path. ponded to 50 km, but it could also be used for an indica- For range measurement, another special "dash system" tion at, say, 20 km. Switching to a frequency 10 percent was developed at Rechlin. A transmitter tunable between higher extended the range to 32 km, and so on. Little more, 42 and 48 MHz was modulated for 10 seconds at 300 Hz; unfortunately, is known about this method. its signal was received in the aircraft on a later mark of Herzog's receiver - now the FuG 17 E and on the First trials German production line. Its output was fed through a tone These systems were, however, only useful for random filter and the resulting note modulated an airborne trans- location at first. Only an all-round representation of an air- mitter, which returned the signal to the ground on another craft was given. For example, the aircraft flew to a given frequency in the 42 to 48-MHz range. There the returned point by standard navigational methods and its range was modulation note was compared with the original one sent then measured by these various electronic systems. Its from the ground and the phase difference, after deduction approach to the point was ascertained by coupling the sys- of the time lag in the aircraft's equipment, gave a direct tem to an -shortwave Adcock direction finder, code measure of the range between the ground transmitter and named Heinrich. Variants of the earlier X-Gef%tsystem were the aircraft. often incorporated wherein a director beam was used. But

Ham Rad~olOctober1989 53 SCHMI TT TRIGGER ARRANGEMENT

TRANSMITTER

LIGHT PUL SER TIMER lCLOSED EVERY 20 SECONDS , FOR 5 SECONDS1 1 dl

I I SCREEN WITH CIRCULAR RALIGE-SCALE * SCALE SSkm INDICATOR - TONE - GENERA TOR

Y-SYSTEM RANGE -MEASUREMENT "ELECTRICAL"

AMPLIFIER

fl f 2

KEYlffi

FILTERS u n d 1 v 5OOhm RECN VER RECN VER COARSE o 5Okm FINE PHASE-CONVERTER FILTERS DIRECTION Y-SYSTEM RANGE - MEASUREMENT "MECHANICAL" METER LIR~

Block dlagram of the Y-system range-measurement systems, electrical and mechanical. the place where the old cross beams would have been Keying the system was originally effected by mercury employed, instead of the X-Uhr combined clocklcalculator, switches or vacuum relays, but as they gave rise to key would indicate the precise timing according to range meas- clicks, they were replaced by the so-called "capacitive mill" urement from the ground. On approaching the bomb designed by a Dr. Escherish. This was a motor-driven release point the X-Uhr received a 9-second Morse signal. differential capacitor which used a light bulb to take the The bombs were released on the last dot. transmitter load between the pauses in transmission. The long lobed direc:tional antennas were keyed at 176 pulses Final form per minute followed by the cardioid-shaped dipoles. This In 1940, under the direction of Dr. Plendl, a development resulted in a slovvrer dotldash pulse with much shorter gaps was devised from this method by Dr. Herzog. This new sys- at a ratio of 8.83, and was acoustically more acceptable. tem retained the code name Wotan 2. Its full title was the In addition, a new receiver based upon Herzog's FuG "Y-Double-Beam Beacon System" and it included parts of 17 E was developed by Dr. H. Donn and Dr. W. Hepper; the multibeam system already described (see Figures 2 it was designated the FuG 28a and manufactured by the and 3). Heliowatt Company. This was combined into one unit with Although the same rotating installation with transmitter Plendl's improved AW 28 analyzer. The latter contained a and operating cabin was used, new antennas were motor driving a c:am making 180 contacts per minute, which introduced with seven parallel dipoles and reflectors, which conducted the receiver output to two series-connected generated a long club-shaped lobe with smaller side lobes. capacitors. Their differential voltages then biased the grids At a half wavelength in front of these were two further dipoles of two valves so that one was bridge switched. A balance spaced at a wavelength apart wh~ch,on an opposlte phase, existed if the field strength of the two pulses from either produced a "washed out" cardloid pattern. Thus two sets transmitter was the same; that is, if the aircraft was found of beams were sent out - one for the flight path to the on one of the two beams. Variation to left or right gave target, and the other for the aircraft's return. (Refer to Fig- opposing bridge currents, with corresponding responses ure 4.) on the indicating meters.

54 Ham Radio/October 1989 seemed to involve a d~rectorbeam plus a means for rang- London, Jones a17dCharles Frank were able to make the ing. Jones's suspicions were aroused when on October 6 following interpretation: an Enigma transmission to what appeared to be a station Objective Distance Rhumb Magnetic called "Wotan 2" northwest of Cherbourg read, Target no. to Poix bearing variation 1 for "Y" coordinates 50°41'49.2" north, 2°14'21.2ff west. to Poix Study of a map revealed these to be the coordinates of London 244 km 142' 10° an army depot at Bovington in Dorset. They showed a great Sheffield 454 km 149' 11' difference from the X-Geriit system in which a number of Bristol 372 km 120' 11' beam directions were always sent out, each station havlng Southampton 272 km 117' 11° to set its beam in the required direction. With this new Birmingham 405 km 137' 11' method, however, the position of the target was given to Homeward flight a single station, which suggested that the station had the entire means of directing the bomber to its target. This The second table in the notebook gave: seemed to be confirmed when Bovington was attacked a Hinflug few days later by two aircraft with results which, though 294 10 somewhat inaccurate in direction, were good as regards 318 11 the range. 283 I1 274 11 302 11 Frequencies and cyphers By assuming that these entries referred to the same cities as those in the first table, and that they were bear- Signals Intelligence and our monitoring services soon ings, the intersectton point appeared to be at Cassel in north began to report the existence of beams on frequencies France, which gave them: between 40 and 50 MHz which had very different charac- Outward flight teristics from Knickebein and X-Geriit. Instead of the left and Objective Approach bearing Magnet~c right transmissions being modulated with dots and dashes, from Cassel variation the emissions were of equal duration - except for a short London 294' 10' pause in transmission when one signal, for example the left, Sheffield 318' 11' came directly after the pause and the other signal followed Bristol 283' 11' in a sequence thus: pause - left, right, pause - left, and Southampton 274' 11° SO on. Birmingham 302' 11' Dr. Robert Cockburn and his assistants at the Telecom- Jones could therefore deduce that: munications Research Establishment put the signal on an (a) the aircraft approached its target from the direction of oscilloscope, and immediately observed its principle. The Cassel; (b) the pilot was not concerned with distance cal- beam emitted three directional transmissions per second culations, which would be consistent with the distance and seemed to have been designed to operate a beam fly- being determined by a distant ground station; and (c) after ing indicator in the aircraft. As things turned out, more sur- the plane had reached its target, the pilot intended to return prising developments were to be revealed. directly to an airfield near Poix. And since he was navigat- Jones discovered that the aircraft using the new system ing on his own, he needed to know the distance from the were not from K.Gr.lOO but from the Third Group of KG 26. target back to Poix - as well as the direction. He also learned that the scientist who had developed the A third table in the notebook contained the frequencies system was none other than Dr. Plendl who had devised for both the bearn itself and the ranging system. Typically, X-Gerat. Plendl was the German equivalent of T. L. Eckers- the station radiated a sinusoidally modulated signal to the ley, our leading radio propagation expert. When Jones aircraft on 42.5 MHz and its modulated note was then asked Eckersley what he thought of Plendl he replied, "He's detected, amplified, and used to modulate a transmitter in not much good, he bases his theory on experiment!" the aircraft, which sent a signal on 46.9 MHz back to the (Amateurs please note!) ground station. The distance of the aircraft was determined On January 19, 1941, an aircraft of KG 26 was shot down by the delay in the return signal. As we know, an analyzer and, though it was badly damaged, it could be seen that was used. it carried equipment similar, though not identical, to X-Gerat. But of greater significance was the radio operator's charred The delicious leg pull! notebook: From a securilty viewpoint it is remarkable that the Ger- mans failed to ensure that notebooks and tables giving Loge 244 142 10 important inforrriation were not taken aboard aircraft. It Schmalstigel 454 149 11 would have been a simple matter to memorize these things Bruder 372 120 11 for a single operation. On the other hand, it could be said Suden 272 117 11 that the Germarls were completely unaware that we had Bild 4 05 137 11 broken their Enigma signal system, which gave away so much more vita information. At all events, these matters added up to British intelligence being able to glean much information which the enemy confidently believed to be Knowing that KG 26's base was at Poix, southwest of secure. Amiens, and that "Loge" was the German code name for Dr. Jones immediately spotted a "delicious" method of

56 Ham Radio/October 1989 upsetting the Y-System, as shown in Figure 5. (Doubtless Jones advised that for the first few nights only a minimum his prowess in practical joking came to his assistance here. of power should be used, just enough to inject a small After all, if disguised as a telephone engineer he had been signal into the Y-System to give the Germans a false range able to persuade an Oxford physicist to plunge a telephone without arousing their suspicions (a process of "acclimati- into a bucket of water, finding a way to bamboozle the zation" by slow change). The first results were not only suc- enemy was likely to come quite readily to mind.) We in cessful, but afforded a source of innocent merriment. One England could receive the 46.9-MHz signal from enemy air- aircraft became ir~volvedin an acrimonious exchange with craft even better than their ground station could, and so the ground station, who suggested he must have a loose we could re-radiate the already re-radiated signal back to wire in his receiver and that he should abandon the attack the aircraft on 42.5 MHz, the frequency used by the ground stat~on.As Dr. Jones pointed out, "This would therefore be fed into the aircraft receiver, along with the signal coming in from the ground station, and in turn be fed back to the ground station again. The effect would be rather like that which occurs in public address systems where the noise from the loudspeakers impinges on the original micro- phone, and is therefore p~ckedup and relayed back to the speakers again. It would appear to the ground station that the aircraft was at a false distance, because the returning waves would have traveled round an extra loop between the aircraft and our own station before getting back to their original base; and if we used a powerful transmitter our- selves, the whole system would ring just as a public address system squeals if the gain of the amplifier is made too high." The BBC television transmitter at Alexandra Palace was just right for the task because it operated in the right fre- quency band. Dr. Cockburn immediately requisitioned it for the purpose and it transpired that this countermeasure, Officlai German diagrams of antenna patterns for (left) return path code named Domino, was first put to use the very n~ght and (right) directional pulsed beam. that KG 26 took over from K.Gr.100 - because we had now successfully jammed X-Gerat.

BOMBER

I CASSEL ALEXANDRA PALACE

AIRBORNE RX Ah'D TX WITH THE PLENLX ANALYSER

CASSEL

The method of interfering with the Y-beam system and the ranging principle of the Y-system.

58 Ham Rad~o/October1989 for that night. Over the following nights Alexandra Palace and especially to Dr. Colin Hamilton, manager of the Air- gradually increased its power and the Germans woke up borne Early Warning Department, for his kind assistance to the fact that we were now successfully jamming the sys- and advice. I am also grateful for the help received from tem, whereupon they abandoned it. some old and respected opponents, notably Herr Fritz Dr. Jones's original aims were that, since he was not Trenkle, author of Die deutschen Funk-Navigations und entirely sure for how long the Germans had successfully Funk-Ftihrungsverfahrenbis 1945; Dr. Rudolph Kuhnhold, used the system, he should break their confidence by mak- designer of the Freya and Seetakt radars; the late Profes- ing them think that we had been interfering with it in a way sor Dr. Wilhelm T Runge, designer of the Mannheim, that had remained undetected for considerable time. This Darmstadt, Wijnburg and Lichtenstein series of radars, who policy reaped further (and at times hilarious) bonuses was able to give valuable help regarding Telefunken's work because once the Germans suspected we were interfer- in the field of beam systems; and Dr. Herbert Kummritz, ing with the system other alarms entered their heads. 'Since Dr. B. Rdde and Dr. Gotthardt Mtiller. the aircraft had to be instructed by the ground station when to release its bombs, it had to be monitored all the time Further reading during its bombing run, and the ground station could han- Most Secret War by R. V. Jones. Published by dle only one aircraft at a time. The aircraft would therefore Hamish Hamilton. fly to a convenient area from which it could be ordered onto The Bruneval Raid by George Millar. Published by The the beam by the ground station, and so commence its Bodley Head. bomb~ngrun. In principle, all we needed to do was trans- The Ultra Secret by F. W. Winterbotham. Published by mit false orders to the aircraft. In fact we did not do this, Nicolson. but it seemed such an easy countermeasure that the Ger- The Rise of the Boffins by Clark. man crews thought we might, and they therefore began to Instruments of Darkness by Alfred Price. be suspicious about the instructions they received." For our German speaking readers: Substance was added to this later when an aircraft was Die deutschen Funk-Navigations und Funk-Fuhrungsver- ordered by the ground station to steer due west (possibly fahren bis 1945 by Fritz Tienkle. Published by Motorbuch because it was east of the beam) to bring it onto the start Verlag. of its bombing run. Failing to hear further ground station Repr~nredw~th permlsslon from Praclrcal Wireless, PW Publlsh~ngLtd . March 1988 Ed orders, the aircraft flew a considerable distance west, then returned to base to complain that the British had given false orders. On other occasions, when the power of Alexandra Palace had been increased, aircraft became confused and were ordered back to their bases after being told, again, 6SAI BOOKS published by Bill Orr, W6SAI and Stu Cowan, W2LX' that a wire was probably loose somewhere in the equip- ment. 'What with our real countermeasures and those BEAM ANTENNA HANDBOOK imagined by air crews, Yoperations became a fiasco Completely revised and updated with the latest computer generated information on BEAM Antenna desl n Covers HF and Yagis and 10, 18 and 24 MHz WARC bands. and the system was withdrawn; we had restored our moral Eve In you needkknow. 204 illustrations. 268 pages. 01985. Revised 1st edition. ascendency for the rest of the wintes" O#h-e61 Soltbound $11.95 Only later did Dr. Jones learn that the Y-System was really AUABOUT VERTICAL ANTENNAS Theory, design, construction, operation-are fully covered. Here's what this exciting Wotan 2, and X-Gerat was Wotan 1. 'And so, while Wotan book covers: Horizontal vrs verhcal-which is best? Top loaded and helical antennas. may have had one eye for 'Y,' he could not have crossed 5 hi h efficienc Marconi antennas for 80 and 160, verticals and TVI-Is there a problem? The eiects of ground on vertical antennas and a how to make an effective eyes for XI.." In fact the Y-System was nicknamed "Benito" ground system, the Bobta~lbeam, construcbon data for 25 different antennas matchm circuits of all descriptions-which is best, plus P-L-E-N-T-Y more! 1st edition, 198 because Mussolini was considered to be the one-eyed end pages O 1986 of the Axis! RP-VA Softbound $10.95 So ends the battle of the beams. I hope that some interest RADIO HANDBOOK 23rd Edition may have been aroused in you to study this aspect of scien- Here are some of the highliihts of this exciting new edition: New easy-to-use charts for Chebyshev and e ~ptlcfilter configurations, new data on ower MOS- tific warfare further, and to live again those momentous days FETS, how to use state-of-the-an DFAMPS, and home computer R!TY to name of the 1940s in the company of such distinguished (if then 'ust a few examples. New rolects include: GaAsFET reamps for 902 and 1296 hz, earto-bull! audio C& filter. Economy M 3-5hZ. 180 meter amplifier. secret) servants who unraveled the enemy beam systems. multiban amp using two 3CXBOOA7's, and a deluxe amplifier with the But to one man, above all, must go the highest recogni- 3CX1200A7 tube. New antenna projects inchde: efficient Marconi design for 160 and 80 meters, computer generated dimensions for HF-Yag~s,and a 2 meter slot tion: R. V. Jones, the young scientist who defied the experts, beam. Get your copy today. 23 edition 0 1986 confounded officialdom, and quietly saved the country from 022424 Cg. 529.95) Hardbound 526.96 a terrible disaster - yet inexplicably, is still denied the THE RADIO AMATEUR ANTENNA HANDBOOK knighthood he so richly deserves. The man who, to repeat A wealth of projects that covers verticals, long wires, beams as well as plenty of other interesting designs. It includes an honest jud~ementof gain fi ures. Churchill's words, 'broke the bloody beams." how to site your antenna for the best performance, a look at Me ~agi-badcon- troversy, baluns, slopers, and delta loops. Practical antenna projects that work! Acknowledgments 190 pages. 01978. 1st edition. ORP-AH Mbound $11.96 I am grateful to Professor R. V. Jones, Emeritus Profes- Please enclose $3.75 for shipping and handling. sor in the Department of Natural Philosophy, University of Aberdeen, for his kind help and advice, and also for his HAM permission to use extracts from his book Most Secret War, RADIO BOOKSTORE publ~shedby Hamish Hamilton. My thanks must also go GREENVILLE. NH 03048 to AEG (formerly Telefunken) for their permission to use extracts from Die deutschen Funklenkverfahren bis 1945,

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