JANUARY 1988 £1·20

BATTLE of the beams BUILD the p\N'otter' 50MHz receiver REVIEVV of the 'revex' \Nave monitor

www.americanradiohistory.com JANUARY 1988 (ON SALE 10 DECEMBER 1987) VOL. 64 NO. 1 ISSUE 970

23 Dipoles Apart R, H, Pearson G4FHU 24 PW "OHer" 50MHz Receiver Mike Rowe G8JVE 30 Understanding Smith Charts-2 Capt, c, A. King 33 Errors and Updates Semiconductor Tester, Dec, 1987 34 Whence Came Shack? Stan Crabtree G30XC 36 Practically Yours Glen Ross G8MWR 37 Computing Comer Paul Newman 43 Battle of the Beams-I D, V, Pritchard G4GVO 48 IC of the Month Hitachi HA-I 397 Audio Ampl111er BrianDance 50 PWRevlew Revex Wave Monitor Scope Mike Richards G4WNC

52 Making Waves~ Guide to Propagatlon-2 A. J, Harwood G4HHZ 54 Expedition to the Pole Laurence Howe11 GM4DMA 61 This Is Thames Coastguard J, D, Harris G3L WM

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www.americanradiohistory.com Feature The Battle of the Beams-Part 1 1940 . .. Now, nearly 50 years onfrom those near-disastrous days, how many ofus remember (or even know oj) the debt ofgratitude owed to one man who confounded the radio experts, overcame officialdom-to earn Churchill's praise as the man who "broke the bloody beams "-and went on to unravel the secrets of German radar and Hitler's "V-weapons": the VI pilotless flying bomb (the "doodlebug'') and the V2 rocket? But for Professor Reginald Victor lones our official language today might well be German. D. V. Pritchard Dip Ed G4G VO tells the story.

Born in London in 1911. R. V. lones · was educated at St. lude's. Herne Hill, and later at the Elementary School in Sussex Road, Brixton, where he won a scholarship to Alleyn's School, Dul­ wich. Awarded an Open Exhibition in 1929 to Wadham College, Oxford, he worked in the Clarendon Laboratory under the formidable Professor Lind­ mann (later Lord Cherwell and Win­ ston Churchill's wartime Scientific Ad­ viser), where he turned his talents to infra-red detection-an interest he was to pursue for the next 30 years. Fortunately for us, in 1939 he was appointed Scientific Officer to the Mil­ itary Intelligence Service (MI6) to find out what the Germans were doing in the way of applying science to warfare, Front view of a small Knickebein array and in early 1940 he came to believe that they had a radio-navigation sys­ accuracy of less than a kilometre. He Amateurs and tem by which they hoped to bomb also added that Knickebein was in accurately at night. some ways similar to X-Gerat, assum­ Experts ... ing that we were familiar with both Obviously beams less than a kilo­ Knickebein-The systems! metre wide at well over 300km called From the wreck of another Heinkel a for very high frequencies-possibly Crooked Leg diary was rushed to lones. It read: something in the centimetric region From captured documents found in March 5. Two-thirds offlight on leave. -and although this part of the spec­ crashed German aircraft he came Afternoon training on Knickebein. col­ trum was in some use at the time, the across the word Knickebein. or lapsible boats. etc. power generated by valves then avail­ "crooked leg", The Germans were ri­ By this time the cryptographers at able was very low. Certainly the Ger­ diculously informative with their code­ Bletchley Park performed a near-mira­ man system suggested they had over­ names-it even sounded like a beam. cle by breaking the German Enigma come the problem. (It was only later But what kind was it? code. One of the intercepted messages that we discovered that German radar Then two prisoners of war in conver­ from a German aircraft was sent to had been operating on 50cm since sation were heard to speak of some­ him: Knickebein. Kleve. is confirmed at about 1930!) thing called X-Gerat. or "secret appara­ position 5T24' north and r west. This However, Rowley Scott-Farnie tus"; evidently it was something used meant that the aircraft had reported G5FI, then a signals officer in RAF in an aircraft and involved radio receiving the beam a few miles south of Intelligence, showed lones a report by pulses. A thriller could hardly have a Retford in Lincolnshire, and K1eve T. L. Eckersley, the country's leading more intriguing title, but what was X­ (where Anne of Cl eves came from) was propagation expert, in which Eckersley Gerat-and was it the same as Knicke­ on the nearest German soil to England. had computed the possible range of a bein? Deeply interested, lones pressed But, clearly, there had to be two 20cm transmitter sited in the Hartz his Intelligence sources for more infor­ beams: one along which the bomber Mountains. If the calculations were mation and in March he was rewarded flew, and another one-a marker correct the signals would bend round with the navigator's notes from a shot­ beam-to tell the pilot when he was the earth and might well be heard by a down Heinkel: Navigational Aid: Ra­ approaching his target. Evidence of bomber at 20000 feet over England. dio Beacons working on Beacon Plan this second beam arrived a few days This information, together with the "A ". Additionally from 0600hr Beacon later in yet more salvaged papers from evidence he had already collected, Dii.hnen. Light Beacon after dark. a crashed Heinkel: Long- range Radio prompted lones to alert Professor Lin­ Knickebein from 0600hr on 315°. Beacon: Knickebein (Bredstedt) 54°39'. demann to the possibility that the Shortly afterwards a co-operative 8°57'. Knickebein (Kleve) 5r47'5". Germans had a narrow-beam system prisoner said that Knickebein was a 6°6'. for bombing the country. Lindemann beam so narrow and exact that two of So Bredstedt in Schleswig-Holstein naturally countered with the objection them could pinpoint a target with an was the source of the second beam! that the frequencies they would have to Practical Wireless, January 1988 43

www.americanradiohistory.com use could not possibly bend round the earth, but Jones produced Eckersley's calculations and told him that indeed From receiver they could. c Pulses But how were the Germans doing it? (a) 11 J - Inspection of captured aircraft re­ Modulation- a vealed nothing unusual and the radio note 11 To instruments equipment seemed perfectly normal -certainly nothing in the way of centi­ metric receivers. He pressed for yet 1 more information, especially from the -I~0f- '-1 --i prisoner-of-war interrogation centres. I I 0 I Pre-approach indication Did their aircraft carry special receiv­ ]J, ~~ Hm (700Hz) ers for beam reception? Had we missed I '1fJ5 something? I 1 Quite correctly the prisoners admit­ ...: ~Ol-- , ted nothing. But at one centre a prison­ , I , ~ Fine-approach indication er was overheard to tell his friend that (b) rnfAf1IElf]E) 7-9 m(1100Hz) I no matter how hard we looked for the I equipment we would never find it. I This startled Jones, for it implied that I ...: 1;. I---1. . I it was under our very noses and there­ I 8, 8 I fore we would never see it. Methodical­ ~ ~ Starboardl . . ly he sifted through the captured ~ t[ Port Equlslgnal equipment but the only item that fitted f the bill was the receiver marked E BI I 1---1 sec .; 9m (1150Hz) IWOH1S71 (Empfanger Blind I )-Blind Landing Receiver Type I-which was used by both the RAF and the LuftwatTe for Fig. 1.1: The target-approach indication with the Knickebein sys­ blind landing on the Lorenz Beam tem. (a) Pulse rectifying circuit. (b) Pulse-rate timing-distances in System. metres, tones in hertz (for approach on flightpath) The Lorenz System, however, only had a range of about 8km at best, unless the Germans has somehow dra­ matically increased its range. Knowing that Farnborough had evaluated the equipment, he enquired if there was anything unusual about the receiver. "No," came the reply. "But since you mention it, the receiver is many times more sensitive than they would (c) ever need for blind landing." (c) Pulse-rectification Could that be it! Or Jones spoke to and wave-forms (A) Lindemann, who drafted a note to tone-modulated signal. Churchill: "There seems some reason (8) At rectifying circuit to suppose that the Germans have some and (C) as final pulse Dot-zone Approaching the Dash-zone type of radio device with which they equisignal hope to find their targets. " Churchill initialled the note and sent tion at Stollberg, also in Schleswig­ manders-in-Chief of Bomber and it to the Air Minister, adding: "This Holstein, and also Scott-Farnie's Fighter Commands). Breathing his seems most intriguing and I hope you guesses about the frequencies. Yet af­ apologies to the Prime Minister, Jones will have it thoroughly examined. " ter two flights the Ansons failed to find took his place at the end of the table. A committee of enquiry was formed the beams. An argument was taking place: did the and Squadron-Leader R. S. Blucke was Was Jones wrong after all? Many beams exist or didn't they? Soon Jones put in charge of flying operations. thought so. Sir Henry Tizard was scep­ realised that nobody in the room knew Three Ansons were fitted with suitable tical (and fell from Churchill's favour as much about the matter as he did. receivers and flown by Lorenz-trained as a result); Air Chief Marshal Dowd­ Suddenly Churchill snapped a ques­ pilots. Rowley G5FI, told Jones that ing was doubtful and Air Chief Mar­ tion at him, and feeling he couldn't the German pre-set frequencies were shal "Bomber" Harris was scathing. answer it out of context Jones said, likely to be 30, 31.5 and 33.3MHz, and Other military and scientific brains "Would it help, sir, if I told you the sure enough a few days later a scrap of looked askance at the young man who story right from the start?" Churchill paper recovered from yet another questioned established wisdom. Then seemed somewhat taken aback but crashed aircraft read: Knickebein suddenly on the same morning Jones then replied, "Well yes, it would." (Kleve) 31.5. was summoned to a meeting at Down­ For the next 20 minutes Jones out­ On June 20 a Heinkel was shot down ing Street. lined his evidence. As he later recalled and the radio operator, who had baled Thinking the message was one of " . .. although I was not conscious ofmy out, had torn his notes into shreds and Scott-Farnie's practical jokes, he ar­ calmness at the time. the very gravity of was actually burying them when he was rived half an hour late to find the the situation somehow seemed to gener­ captured. An Intelligence NCO un­ meeting already in progress. A galaxy ate the steady nerve for which it called. earthed them, gummed them together of talent confronted him. Churchill sat Although I was only 28. and everyone and sent them to London: VHF. on one side of the table flanked by else around the table much my senior in Knicke 54°38' 7" N. 8°56'8" E. Lindemann on his left and Beaver­ every conventional way. the threat of 51"0' 30" N. Eqms.. Stollberg 30mc/s. brook on his right. Facing them was Sir the beams was too serious for our Kleve 51"4 7'N. 6"2'E. 55 oN. 2°Eqms .• Archibald Sinclair (the Air Minister), response to be spoilt by nervousness on 31.5mc/s. Sir Cyril Newall (Chief of the Air my part." This seemed to confirm the exis­ Stafl), Sir Henry Tizard, Watson-Watt, When he had finished an air of tence of another Knickebein installa- and Portal and Dowding (Com- incredulity filled the room. Sir Henry 44 Practical Wireless. January 1988

www.americanradiohistory.com T izard demanded to know why the Black Night and synchronised with the south(!rn beam. Germans should use a beam anyway, apparently passing through a point near assuming such a thing was possible Bright Dawn Beeston on a bearing lying between -our own pilots found their targets Or Jones went home to spend one of 60°+ and less than 104 °. very well by astro-navigation. (They the most miserable nights of his life. In other words the director beam didn't!-Author.) Others round the ta­ "Had I, after all, made a Iool oImyself was aimed at Derby where the Rolls­ ble seemed doubtful. But Churchill and misbehaved so spectacularly in Royce factory produced engines for the was convinced and asked Jones what Iront oI th e Prime Minister? Had 1 RAF-as Jones had suspected. The should be done. jumped to Ialse conclusions? Had I impact of Bufton's report on the meet­ "I told him that the first thing was to la lien Ior a great hoax by the Germans? ing that afternoon may well be imag­ confirm their existence by discovering AbOl'e all, had 1 arrogantly wasted an ined. Jubilation was in the air. Even and ./lying along the beams Ior our­ hour o[th e Prime Minister's time when " Daddy" Nutting was skipping round selves, and th at we could develop a Britai;l was about to be invaded or the room in delight. All doubts were variety oI countermeasures ranging obliterated from th e air?" now dispelled and countermeasures [rom putting a Ialse cross-beam Ior It was a beautiful summer's could go ahead urgently. making th e Germans drop their bombs night-the shortest night of a terrible In the midst of the revelry Scott­ early, to usinglorms o.fjamming rang­ year for Britain-when Flight-Lieuten­ Farnie button-holed Jones: "Remem­ inglrom crude to subtle." ant Bufton and Corporal Mackie ber what you said yesterday?" With a typi cal " Let this be done at climbed aboard their Anson and flew So they bowled across to a pub to once!" Churchill then turned round over the area between Huntingdon and celebrate. and tore a strip off the Air Ministry for Lincoln. Neither had been told the their tardiness. Knickebein story, but merely to search' The Lorenz System for beams with Lorenz characteristics. In 1932 a Or E. Kramar of the And Expert Suddenly on the Hallicrafters receiver German Lorenz Company began to they heard signals on 3I.SMHz. Dots! develop a high-frequency blind-land­ Amateurs ... The aircraft swung to the north. Still ing system on pre-set frequencies Elated at having convi nced the dots. Then- a continuous note, and between 30 and 33.SMHz, continuous­ Prime Minister, Jones dashed away to later, as expected, a zone of dashes. wave modulated at IISOHz. The bea­ attend a conference in the offi ce of the When the dashes ceased Bufton and con transmitter and its associated an­ Director of Signals, Air Commodore Mackie began intently to plot the tenna system stood at the end of a Nutting, to discuss the possibility that beam. The following afternoon Buf­ runway and had a range of 3-Skm the Germans might ex ploit pulse tech­ ton's report was on Jones' desk: (sometimes more depending on condi­ niques as navigational aids, and on (I) That there is a narrow beam (ap­ tions) even though the transmitter de­ which T. L. Eckersley was to give proximately 400-500yd wide) passing veloped SOO watts. The output was fed evidence. However, because Eckersley through a position 1 mile south of to a single dipole, to the left and right disagreed with Jones' findings, the Spalding, ha ving dots to th e south and of which and at a ! -wave spacing, was a subject reverted to Knickebei n. dashes to the north, on a bearingoI 104° single reflector cut at its centre point. A But what about those propagation (2847). relay was employed to alternately close calculations? Oh, those! Eckersley (2) That the carrier frequency of the and open the reflector, as shown in Fig. pooh-poohed them: he didn' t believe transmissions on the night oI 21122 1.3, whereupon a beam was generated them himself. He was onl y trying to June was 31.5mcls, modulated at 1150 at an angle left and right of the driven demonstrate how far the signals might cycles and similar to L oren z element composed of dots to one side go under certai n conditions. He characteristics. and dashes to the other (Fig. lA). thought he had been stretching theory (3) That th ere is a second beam having These alternating beams partially over­ too far, and doubted if sign als in the similar characteristics but with dots to lapped each other centrally to give a 30MHz band would curve round the th e north and dashes to th e south narrow zone of about 3° angle in which earth. Fig. 1.3 The Ansons had failed to detect the On the Equisignal, dots exactly ~ beams during their previous flights and fill the gaps between the dashes, Reflector 1 Driven element Relector 2 another one was due that evening. In so that the pilot hears a continuous note . order to cancel it the Principal Deputy­ Director of Signals, Group Captain O. Equisignal beam 1 G. Lywood, picked up the phone say­ Relay 2 ing, "Well we have here th e greatest expert on radio propagation in (h e country (author's italics) and he says . / \ ;"''' r / . the beam theory is all wrong. We've / I wasted a lot of time and let's not waste Dot zone . / / any more. This evening's flight should / jDash be cancelled!" But Or Jones stood his I I zone I Lj ground. Pointing out that Eckersley's I I Cam-switch evidence had neutralised itself because I / / (motor driven I Antenna feed he had said one thing a few months I / / §l §l1§I1§! before and now said something quite / / Time- different, and that enough evidence / / already existed to convince him, he / / / demanded that Eckersl ey's statement ..... /' should be ignored. He also told ~ Transmitter switched from Dash Lywood that if the flight was cancelled ~ antenna to Dot antenna alternately. he would "jolly-well let the Prime 1650 angle Fig. 1.2 Minister know who had countermand­ ed his orders." Lywood backed down. Fig. 1.2: The principle of the Lorenz From the Chair, Air Commodore (Knickebein) beam Nutting demanded: "And what do we Fig. 1.3: The principle of the operat­ do if we find the beams?" Quietly ing reflectors Jones whispered to Rowley Scott­ Fig. 1.4: The principle of the Lorenz Farnie, "Go out and get tight!" beam system Practical Wireless, January 1988 45

www.americanradiohistory.com the dots and dashes were heard as a ceivers used are, unfortunately, no Pulling the single note, thus telling the pilot he was longer in existence, but the antenna on the correct approach. A simple lobes were similar to those shown in Crooked Leg presentation unit was also provided in Fig. 1.6, except that the narrow equi­ A special unit was set up to counter the cockpit which showed the course­ signal zone was ± 0.3° wide and the the beams (which were code-named deviation on a meter, and a form of keying of the dash-dot system had a Headaches) under the command of range measurement was furnished by ratio of 1:7. The improved receiver, Wing Commander E. B. Addison of an S-meter arrangement. another mark of the EB I known as the No. 80 Wing at Radlett. The technical Two additional transmitters were Fu Bl I, could receive the beam at a design of the countermeasures was the employed to aid landing (Fig. I. 5). At a range of 500km and a height of 6500m. responsibility of Or Robert Cockburn point 3km before the runway was an The principle was that the main beam of the Telecommunications Research early-approach system on 38MHz with was directed at a target and the pilot Establishment at Worth Matravers. a power of SW, 'but having a slower knew he was on course when a contin­ Both organisations were accorded the keying rate and a lower modulation uous note appeared in the receiver; if highest priority. note. The second system comprised a he strayed to the left a preponderance Receivers were placed on top of the transmitter at 300m before the run­ of dots was heard, and a swerve to the masts of certain stations of the Chain way, with a higher key-rate and modu­ right produced dashes. Home RDF (radar) system, and the lation tone. Both these systems operat­ By 1940, 10 smaller versions of unlucky operators in these dizzy crows' ed a lamp on the presentation unit to Knickebein had been built which only nests were connected by telephone give further visual indication. required a circular track of 45m diame­ with Fighter Command Headquarters The accompanying aircraft receiver ter, and each leg of the angled frame at Bentley Priory. was known as the EB I (Blind Landing contained only 4 sets of vertical 2- Professor lones records how he, too, Receiver I) , which was developed element arrays which were broadband­ spent a night on top of one of these fro'm the earlier EBE receiver. The ed to tune between 30 and 33 .3MHz by towers, listening to the signals which system was made available to Luft­ constructing them from wide-diameter Eckersley had said could not be heard hansa in 1934 and the aircraft were tubing. The range was almost the same even by a bomber at 20000 feet over fitted with vertical rod antennas, in practice as the large Knickebein, England: "When about dusk the Ger­ usually !-wave whips. Later, the although the main beam width was man beams were switched on, the men Luftwaffe produced a specification for wider at ± 0.6°. in the towers would be able to pick them what was to be called the Blind Land­ As already mentioned, in use the up and let us know, for instance, If a ing System FuB I, and which required main beam was directed at the target beam was going between tower 'A' and two separate receivers: the EB I for and at a pre-determined point some tower 'B'. That would give us a clue to signals in the range 30-33.3MHz, and distance before it was reached it was the beam's position, and one of our the EBL 2 for 38MHz. All multi­ overlapped by a second beam on a chaps would go up in an Anson and fly engined aircraft of the Luftwaffe were different frequency, thus telling the back and forth until he picked up the fitted with these up to 1941. pilot he was so-many kilometres from beam, which could then be plotted. .. As war seemed inevitable, in 1938 his objective. Fig. 1.6 shows the meth­ The first jammers were diathermy Or Lohmann of Telefunken developed od in more detail. sets used by hospitals to cauterise a much larger system which was called Although no details remain of the wounds. These were requisitioned and the FuS An 721. This was an antenna receivers employed, it is known that tuned to the Knickebein frequencies, array of metal girders 30m high and they were t.r.f. types and, as will be and although they only emitted a mush 90m long which revolved on a circular seen later, very susceptible to jam­ of signals it was thought that they had iron track; in the middle was a 50-watt ming. For this reason a Or W. Kloepfer some effect on the beams. Installed transmitter for 30-33.3MHz. The of Lorenz developed a superhet, the mainly in police stations, they were framework supported 16 vertical wire EBL 3 H, which needed only slight switched on when ordered by No. 80 dipoles and reflectors and was ar­ preparation as it used the same p.S. u. Wing. ranged at an angle of 165° (looking as its predecessor and fitted the same Fortunately we had acquired the down on the array), so that 8 2-e1ement · cabinet. This was tunable over a num­ Lorenz licence before the war, so Lo­ antennas were in each leg of the frame­ ber of channels from I to 34 in the renz transmitters were modified and work. From this " broken neck" ap­ spectrum 30-33.3MHz, and could re­ strategically placed, as were "Mea­ pearance, geknickten in German, came ceive the Knickebein transmissions at cons", or mock beacons. The the code-name Knickebein. the same height and range of the earlier Luftwaffe, with more than 80 radio Details of the transmitters and re- model. beacons at their disposal in Germany and occupied Europe, began to find radio-navigation an ever-increasing problem. But it was Cockburn's jam­ mers (code-named Aspirins) that were WOM 160 most effective. Immensely powerful, they flooded the beams with dashes and the German pilots, flying into their own dash-zones, would steer to find the equisignal only to find Cockburn's lOO ro 335MH, dashes. They would continue turning ~ ~~~/:'::~?::~~T until they found a dot-zone (and Cock­ \ I burn's dashes) which often synchron­ . Main fine approach beacon ised into a false equisignal note. After - _ 38MHz . higher keying rate they had found themselves flying ,- 300m" ~ - / round in circles during bombing raids ----. <- for a few weeks, they came to realise Dot zone that we had found and jammed their ...... " ...... system. We had, in fact, "pulled the 3000m crooked leg". An additional bonus lay

Main fore- approach beacon Fig. 1.5: T he principle of the Lorenz 38MHz, slower keying rate blind-landing system 46 Practical Wireless, January 1988

www.americanradiohistory.com in the fact that it was several months before the German pilots had the cour­ age to tell Goering that Knickebein was useless. Had the system worked successfully a number of bombers could have put a bomb every 17 metres into a selected target. As it was our cities suffered a severe mauling from the Luftwaffe: how much worse the loss of life and property would have been but for the efforts of a yo ung physicist who re­ fused to believe the ex perts. and coura­ geously challenged his superiors. Today one wonders how many Lon­ doners and citizens of our other major cities have heard of Professor R. V. Jones.

In Part 2 o(his series, G4GVO describes ho w th e' X-GerG t mystery was unrm'elled. Fig. 1.6: The antenna pattern of the Knickebein array

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Directivity Gain in Transmitting Antennas The COM IC-761 HF Transceiver Reviewed ______~'C ______~ www.americanradiohistory.com FEBRUARY 1988 (ON SALE 14 JANUARY 1988) VOL. 64 NO. 2 ISSUE 971

20 PWRevlew Icom IC-761 HP Transceiver Ken Michaelson G3RDG

26 Amateur Radio In AustraUa-3 GregBaker

28 Vertical Antennas P. Newton

30 Making Waves-a Guide to Propagatlon-3 A. J. Harwood. G4HHZ

35 PWRevlew S.E.M. QRM Eliminator Geo!! Arnold G3GSR

36 PW "OrwelltJ MW Receiver-I R. F.Ha1gh

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46 BoHle of the Beams-2 D. V. Prltchard G4GVO

49 Errors and Updates Letter-"Morse" . Jan. 1988 Making Waves-2, Jan. 1988

50 Practically Yours Glen Ross G8MWR

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Editorial and Advertisement Offlc.s: Edhor Geoff Arnold T.Eng FSERT G3GSR Practical Wireless Assistsnt Editor Dick Ganderton C.Eng. MIERE G8VFHi; Enelco House Art Editor Steve Hunt '. The Quay Technical Features Editor Elaine Richards G4LFM Poole. Dorset BH 15 1 PP Richard Ayley G6AKG ... Poole (0202) 678558 (Out-ol-hours Technical Projects Sub-Editor service by answering machine) Editorilll Assistant Sharon George Prestel 202671191 Technical Artist Rob Mackie Administration Manager Kathy Etheridge Advertisement Manager CI.rical Assistant Claire Horton Roger Hall G4TNT ... 01 -7316222 Accounts Annene Martin

COPYRIGHT 4:J PW Publishing Limited 1988. Copyright in all drawings. photographs. and articles published in mctjClI Wirell1SS is fully protected BOO reproduction or imitation in whole or in part is e~pressly forbidden . All reasonable precautions are taken by P"ctiClI Wireless to ensure that the advice and data given to oor readers are reliable. We cannot however guarantee it and we cannot accept fegal responsibility for it. Prices are those current 8$ we go to press. Practical Wireless, February 1988

www.americanradiohistory.com Feature The Battle of the Beams-Part 2 D. V Pritchard Dip Ed G4GVO continues the story of the "Crooked Beams" as he tells us about X-Gerat-The Secret Apparatus. As early as 1934, when Knickebein was in its infancy, a German scientist be­ gan to have doubts about its efficiency if exposed to jamming. He was Staats­ rat (Privy Councillor) Or H. Plendl of the Oeutsche Versuchanstalt fUr Luft­ fahrt (German Aeronautical Research Establishment) and he began to pro­ duce designs for a new system for accurate blind bombing. Under his leadership, a new depart­ ment was formed at Rechlin (the Ger­ man equivalent of Farnborough) which began research in June of that year. This was in co-operation with another department led by a Or W. Kuhnold which was al'so engaged on beam techniques for blind landing. The beams of Kuhnold's system, how­ .._ .... TA"-. -..; . ~... ,.. r.&:, U T."M... " ever, had an aperture angle of about 5°, ..~ __ _ ...... \.~". r ....~I! .. corresponding to an 8km beamwidth at a range of 100km, and were clearly The layout of a typical X-Gerat installation with operating cabin and antenna array of a rotating platform Photogr.ph. by court.. y of Frltz Trenkle unsuitable for accurate pin-pointing of targets. Obviously a beamwidth of not named Bertha / , but as this was not be phased to swing through about 10° more than 0.10 was required and this, powerful enough a second was de­ were used; and the airborne equipment at that time, could only be attained signed, Bertha 2, which delivered consisted of two 1. r. f. receivers devel­ with reasonable antenna dimensions 500W and was tunable over the re­ oped at Rechlin and an analyser for and suitable power if a frequency quired range. unlocking the 2000Hz modulated dot­ between 66 and 77MHz was employed. Preliminary tests carried out over dash system of the adopted and im­ Accordingly, experiments were begun Lake Miiritz near Mecklenburg in proved Knickebein apparatus. Unfor­ with an 80-watt transmitter designed 1935 resulted in ranges of only 1500m. tunately full details of both transmitter by a Or Ochmann which was code- Stationary beam antennas which could and receivers are no longer available.

Fig. 2.1: Block diagram ~ of X-Gerit f~ed sys­ Dipoles Wotan 1 tem and capacity switch for pulsing By 1938, the system had been greatly improved. Or Kiihnold had developed ground installations capable of easy dismantling and removal, with an op­ erating cabin and antenna array mounted on a platform which could rotate through 360°. The antennas )./2 lecher lines were mounted on a gantry and spaced m.o. buffer at 14.75m (3.5 wavelengths). Original­ & lIIod. etc. ly, simple half-wave dipoles were em­ ployed, but before long directors and '---+------' ~ reflectors were added for extra power and range; these were energised with pulses at 120 per minute via a vacuum switch (soon replaced by a capacitor, nicknamed a " mill switch", designed by Or K.H. Fischer). The schematic block diagram of this system is shown in Fig. 2.1 A half-wave Lecher line is used in conjunction with the "capaci­ ty" switch and its associated induc­ tances to pulse both dipoles with the required dot-dash sequence. .... Fig. 2.2: Antenna pat- The array generated a fan of 14 • • tern of X-Gerit beams each with a bandwidth of 0.050 ._ system (Fig. 2.2), and 8 of these installations 46 Practical Wireless, February 1988

www.americanradiohistory.com were erected in Germany, followed by many more on the coasts of occupied Europe. By now the airborne equip­ ment had also been drastically im­ proved by Or H. Hanel and Or Rucklin of Telefunken, who had designed and developed a superhet for 66 to 77MHz (code-named Anna), while an analys­ ing system designed by Or Plendl known as the A VP (Anzeige-Verfahran von Plendl) was being mass-produced by Siemens. At the same time a Or K. Muller set up a Mobile Research Unit which produced some versatile mobile sta­ FlIGHT PATH ON DIRECTOR 8EAM Tl OR T1 tions under the code-name Mobelwa­ ITl. RESERVE 8EAM gen or "Furniture Vans". He was also responsible for the clever camouflaging of their antenna-a feature which was 'lIT 2 Tl later to prove troublesome for British Fig. 2.4: German layout of beams Fig. 2.3: Official German layout of • counter attacks. showing main beams and asso­ the X-Gerit system The complete system was known as ciated fans Wotan 1. 1940 is shown in Fig. 2.5, and Fig. 2.6 machine and fed them into a combined is another official German layout calculator and stopwatch called the X­ Principle of showing the disposition of all beam Uhr, or "X-Clock". This was an incre­ systems in use at that time. (In this dibly accurate mechanism designed at Operation series the author has concentrated only Rechlin by a Or Hepper. A small upper One of the 14 beams was selected to on the more widely known systems.) dial on the left-hand side showed how act as a director beam which, on being In practice the bombers did not fly long the instrument had been running, aimed towards the target, provided a along the director beam immediately while the lower dial was used for flight-path for the aircraft; this system after take-off, but used either normal calculating the "flight-path ra­ was similar to Knickebein in that the navigational methods or one of the fan tios"-that is to say, information pilot could plot his course according to beams in order to present a smaller about the aircraft's type, height and a direction indicating meter which told target for British radar and to try and speed was inserted to give a flight-path him if he was right or left of the beam. cause confusion. The director beam ratio of, say, 2.78: 1 for 18km, or 3: I for The official German layout of the was usually joined sometime after 6km according to circumstances. beam approach system and its asso­ crossing the English coast. On arriving in the dash-zone of the ciated cross beams at points before the At approximately 30km before the advanced cross beam the operator target is shown in Fig. 2.3, while Fig. target, the aircraft would encounter the would listen for the (very brief) contin­ 2.4 represents not only the director coarse advanced cross beam which, uous note produced by the merging of beam and reserve beam, but also the like the other beams, was similarly dots and dashes, and press the clock's cross beams and the associated fans of pulsed with dots and dashes but on a top button. This started the green beams which enabled stray aircraft to different frequency. Before reaching "minute" hand and the black sweep­ plot their courses to the correct one. this point the bomber's radio operator hand simultaneously and, according to The main beams of the system used for would have consulted a table giving the the inserted data, the time taken for the the devastating raid on Coventry in characteristics of his particular type of bombs to drop was now fed in. IMMI ~ Fig. 2.5: The X- r/-~i;!C==+======il!lii:=--71 Gerat system for K. Gr. 100

Fine X-Bums u set for Coventry 14/15 November 1940 : ::~} )0D.· It. ItJ'IIC1aUIJlI...... W1'AN I t • x. • T. WO'1'A..~ II " t. t.na.oP

Fig. 2.6: Official ~ German layout showing the dis­ 9 59 '90 150 290 position of all Kilometres beam systems in .... "" L-______--' use at that time Practical Wireless, February 1988 47

www.americanradiohistory.com At the "fore-cross-signal" a button missed; and when he obtained further on the left was pressed whereupon the confirmation from the two crystals green and black hands stopped and the whose frequencies were not exact or red "hour" hand started. By pressing half integers, the problem was solved. the third button at the main cross Other information that emerged from beam the red hand would stop at the the Anna numbers was that both the same point as the previous ones and, if coarse and fine beams lay between 66.5 the correct data had been given, the and 75MHz. bombs would be automatically released. After tests by a research squadron, Measurement the system was finally installed in Ju 52's and He Ill's of KampfGruppe Inaccuracy 100, a Group led by an outstanding The immense value of Anna Luftwaffe officer, Major Viktor von numbers was that if the transmjtted Lossberg. Quarter-wave whips were Fig. 2.7: aeam patterns of mobile X­ orders to the beam stations could be mounted on top of the fuselage behind Ger't decoded in time, he could then tell 80 the cockpit and these, in conjunction Wing the frequencies to be jammed. with the whip antenna for RT opera­ It was that well-known amateur of Incredibly, his interpretation of the tion which was situated further back, his day, Rowley Scott-Farnie G5GI, numbers was rejected because our gave rise to the nicknamed "Three­ then an officer in RAF Signals Intelli­ monitoring services thought there were master". gence and a close friend of Jones, who frequencies outside the range he had The airborne equipment was in­ reported beam signals from the Calais found. Or Jones' hackles rose-a pos­ stalled in the radio operator's position and Cherbourg areas around 70MHz. ture they were seldom slow in assum­ and repeaters for the course meters By September 24, 6 beam stations were ing-and plain words were spoken. were fitted in the cockpit for the pilot's identified: 2 north-west of Cherbourg, "These, it transpired. were due to bad benefit. A motor generator fed from 3 near Calais and the last near Brest. measurement of the frequencies of the the aircraft's batteries (rotary convert­ The Germans had code-named them German beams on the part of the er) was placed at the bottom of the Weser, Spree, Rhein, Elbe. Isar and countermeasures organisation. a fea­ installation and immediately above it Oder. EvidenUy KGr.1 00 was working ture that was to plague us through the were two audio units, to the left of through a book of numbered targets whole battle. The fault in this case which was the power distribution pan­ and by the time the stations were probably lay not with the observers, but el and, above, the twin receivers for the identified Jones had the actual direc­ with the calibration of our receivers director and cross beams, the Anna tions for the beams-and even that the which were not up to the German receiver being on the right. Germans had specified them to the standards of precision ". His findings nearest 5 seconds of arc, an accuracy of were accepted. about IOm at 320km! Or Robert Cockburn of the Tele­ Intelligence But how could such an accuracy be communications Research Establish­ Breakthrough possible on 70MHz? ment, having successfully prescribed H "Aspirins" for the Knickebein "Head­ The phone shattered Or R.V. Jones' The ··Anna aches", now developed "Bromides" sleep in the early hours of a morning Numbers for this new system which was code­ during the first week of September, named "Ruffian". We now knew that 1940. Further decoded German transmis­ the director beam was radiated from "We've got something new here! sions revealed the existence of coarse near Cherbourg and the cross beams God knows what it is, but I'm sure it's and fine beams, including a mention of something for you!" from the Calais area; as insurance centimetres. This latter, however, re­ against the failure of the main director The excited voice of Professor Fred­ ferred to the precision with which a beam (Weser) a reserve beam was erick "Bimbo" Norman, a crypto­ monitoring vehicle had to be posi­ provided by the adjacent station grapher at Bletchley Park, shook Jones tioned to orientate the director beam. into consciousness. They had broken (Spree). The accuracy of the beams was Frequent mention of something called so great that in calculating their paths some new Enigma traffic in which "Anna" was made, usually associated it was necessary to take into account radio beams were mentioned, includ­ with a number between 10 and 85, and that the earth is not a sphere, but ing the information that the beam­ often a multiple of 5. By October 17, flattened towards the poles; this made width was 8 to 10 seconds of arc, or an Jones had collected 10, 15, 25 , 30, 35, a difference of 275m in where a beam angle of 1:20 000, suggesting that the 44, 47 , 55, 60, 75 and 85. Another set from Cherbourg would cross London! beam was no wider than about 20m at of numbers gave crystal frequencies 320km! (typically 8750kHz, since 8750kHz x 8 Then came the electrifying word X­ - 70MHz) and he suspected that Anna Gerat! Whatever X-Gerat was, it was referred to the dial on the aircraft Countermeasures being installed in aircraft of Kampf­ receiver, if not the aircraft itself. Since and Counter Gruppe 100, one of the Luftwaffe's one set of numbers ended in 0 or 5, and crack squadrons. the other in 0 or 0.5, simple deduction Arguments Jones hustled the intelligence ser­ showed that the Anna reading had to Cockburn's jammers came into op­ vices into greater activity. Across the be divided by 10 and either added to, eration in October, but at this time . Channel the Resistance organisations or subtracted from, a constant number. KGr.IOO began to drop flares over its pulled out all the stops, and British Learning from the Enigma traffic targets and this was hailed by some of Signals Intelligence (including Volun­ that a certain Feldwebel Schumann at Jones' antagonists as proof that the tary Interceptors-a body of dedicated a beam station at den Helder had beams didn't work, or that the Ger­ radio amateurs) doubled their efforts. signed a return for 3 crystals for 69.5, mans were so unsure of them that they Their activities prompted Jones to 70 and 71.1 MHz and that his station were using flares to find out where they record his appreciation: "Our commu­ was ordered to transmit on Anna were. However, Jones silenced these nity ofradio amateurs in Britain was to numbers 30 and 35, it was clear that critics by pointing out that there was prove an invaluable reserve, both in the constant had to be 66.5 if one-tenth no evidence that K.Gr. IOO was upset Signals Intelligence and Signals proper, of the Anna number had to be added, by our countermeasures (which was as well as furnishing many of the staff or 73 if it had to be subtracted. As he true) and were not only using the for our rapidly increasing number of knew that crystals for 75MHz existed, system, but acting as pathfinders for radar stations ". the second possibility could be dis- other Luftwaffe groups. 48 Practical Wireless, February 1988

www.americanradiohistory.com Yet other problems had to be 80 Wing asked Jones which frequen­ was in the water salvage was a Navy overcome. cies should they set their jammers on, matter and, taking the rope aboard, If the Enigma transmissions to the giving a list of frequencies as deter­ dragged the aircraft deeper into the beam stations could be broken in time mined by our monitoring aircraft. "/ sea, breaking the rope in the process. (they were usually sent out in the could see at once that the measure­ The X-Genit equipment aboard, now afternoon preceding a raid) we would ments must be wrong. in that they did heavy with silt and corrosion, was know where and when K.Gr.IOO was not match up with the figures / knew fortunately discovered and rushed to going to attack, and our fighters could from the Anna code. I therefore made a . 80 Wing and then on to Farnborough be ready for them; our jammers, too, mental correction of the measurements for investigation. could be set on the correct frequencies. as far as / could-for example. 68.6 On November 21 Jones, accom­ For this to be possible the cryptogra­ should have been 68.5. if our receivers panied by Scott-Farnie and their assis­ phers at Bletchley Park strained all had been properly calibrated, or 70.9 tants, went to see it for themselves. their resources-and it was a magnifi­ should have been 71.0. But deciding They learned that Farnborough had cent effort, for they achieved this incre­ what. for example, 66.8 meant was examined the audio filter and found it dible feat late in October. Dr Jones was more of a lottery. The only other clue set to 2000Hz. But our jammers had then able to tell Fighter Command the that / spoiled was that there seemed to been modulated at 1500Hz, which exact place of the attack, the time of be a convention that the director beams meant that while our carrier frequen­ the first bomb to within 10 minutes, would generally be on frequencies cies were correct the modulation tone the exact speed of the bombers, their between 66.5 and 71.5 and the cross had no effect on the beams. line of approach to within 90m, and beams between 71 .5 and 75.0MHz, the "/t was one of those instances, of their height to within 2 or 3 hundred division being presumably due to opera­ which / have since found many, where metres! tional convenience. Remembering that enormous trouble is taken to get the Yet our night fighters repeatedly we needed to knock out the main and' difficult parts right and then a slip-up failed to find the enemy. Jones wrote: reserve director beams and at least one occurs because of lack of attention to a "/ almost began to wonder whether the of the cross beams. / then made my seemingly trivial detail. Ofall the mea­ only use the Duty Air Commodore mental gamble and suggested a set of surements in connection with the Ger­ made of my telephone calls was to take frequencies to Addison which he said he man beams. easily the simplest was to a bet with the rest ofthe Command as to would adopt. All this took no more than determine the modulation note, be­ where the target would be for that five minutes on the telephone: but / was cause this could be done at any time in night ". On top of this was the growing well aware that in these snap decisions / c0'1lfort; and yet whoever had done it suspicion that our jamming was not was probably gambling with hundreds had either been tone deaf or completely working. Why not? of lives. Sobering though this thought careless. and no one had ever thought of The answer soon came-but not was. the fact remained that someone checking his measurements. / was so before tragedy struck. had to do it. and / was easily in the best indignant that / said whoever had made position. " such a mistake ought to have been Then on the night of November shot." It is hard to believe that the 14/15 Coventry was attacked, with citizens of Coventry would have dis­ heavy civilian casualties. What had agreed with this opinion. gone wrong? The next day the decoded Jones' anger was further increased Moonlight Sonata Enigma signals to the beams stations by the fobbing-off he encountered. He On November 10 Jones received an arrived and Jones' wretchedness was told that the modulation note was Enigma decrypt of a transmission to turned to bewilderment. He had originally 1500Hz but the Germans the beam stations which told them to guessed the frequencies correctly-so had changed their filters to avoid jam­ prepare operations agai nst target where was the failure? ming. This ridiculous excuse was coun­ numbers 51 , 52 and 53, giving the tered by Jones who pointed out that if beam settings at the same time. It took that had been the case we would only a few minutes to work out that 51 obviously have heard the change in was Wolverhampton, 52 was Bir­ note for ourselves. In any event he was mingham, and Coventry was 53. Then Incompetence and able to prove that K.Gr. IOO had been another signal was passed to him which using the same filters since the start of contained orders for a major operation Carelessness their operations. under the code-name Moonlight Sona­ The failure arose originally from a On his insistence the jamming mo­ ta. Four target areas were mentioned silly inter-service squabble which led dulation frequency was changed and but there was no indication of the order on to a ghastly mistake. On November when, later, the Germans attacked of the attacks. Frantic guesses were 6 one of K.Gr.1 OO's Heinkels became Birmingham their bombs feU wide of made by the Air Staff and the best they lost over southern England and the target, most of them outside the could come up with was that Moon­ ditched on Chesil Beach. The Army city. Gradually they came to realise we light Sonata might mean a target in took over, secured a rope around the had broken X-Gerat and their confi­ southern England. Strangely, no attack fuselage and set about salvaging it, dence in the system diminished, and had been made on Wolverhampton, when a naval inshore vessel arrived Britain which knew nothing about Or and on November 14 everyone braced and demanded to know what the Army Jones and his scientific war went on themselves for the coming night and thought it was doing. As the aircraft "business as usual". whatever Moonlight Sonata might mean. In Part 3, G4GVO tells how Wotan's "other Tragically, it was one of those after­ noons when Bletchley Park failed to eye' '-the V-System-was successfully countered. break the Enigma signals in time, and ERRORS & UPDATES Letter-UMorse" Making Waves, Part 2 January 1988 January 1988 The Morse code equivalent of "ES" is, of course, "dit di-di­ The decibel equivalent of 50 picowatts is -i03dBW, not as dit", and not as was shown on page 14 of that issue in the let­ shown in the third column of page 52, where the minus sign ter about American Morse. became separated from the figures. Practical Wireless, February 1988 49

www.americanradiohistory.com MARCH 1988 £1-20

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We are sorry that, due to technical d1ff1culties, the promised article about a Digital Dial has had to be held over unW next month

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Editorial and Adverti.ement Off"tee.: Editor Geoft Arnold T.Eng FSERT G3GSR Practical Wireless A ••i.tant Editor Dick Ganderton C.Eng. MIERE G8VFI Enelco House Art Editor Steve Hunt The Quay Technical Feature. Editor Elaine Richards G4LFM Poole. Dorset BH15 1PP Technical Project. Sub-Editor Richard Ayley G6AK .. Poole (0202) 678558 (Out-ol-hours service by answering machine) Editorial A ••I.tant Sharon George Prestel202671191 Technical ArtI.t Rob Mackie Admlnl.tratlon Manager Kathy Etheridge Adverti.ement Manager Clerical A ••i.tant Cia ire Horton Roger Hall G4TNT .. 01-731 6222 Account. Alan Burgess

COPYRIGHT @ PW Publishing Limited 1988. Copyright in atl drawings. photograp/ls. and articles published in PmctiuI KhI8ss is fully protected and reproduction or imitation in wbole or in part is expressly forbidden. All reasonable precautions are taken by PrlctictJlltl'lI1less to ensure !hit the illMce and data given to our readers are reliable. We cannot however guarantee it and we cannot accept legel responsibility for it. Prices are those CIlrrant es we go to press. Practical Wireless, March 1988

www.americanradiohistory.com Feature The Battle of the Beams-Part 3 Ever since 1939, Dr Plendl of the German Aeronautical Research Establishment entertained doubts about the effectiveness ofX-Gertit in the face ofstrong jamming; accordingly, schemes for a new system were put in hand at that time. D. V. Pritchard Dip Ed G4G VO concludes this most interesting story.

Ideally, such a system would have only Schmitt trigger one director beam for the guidance of arrangement the bomber and another for a range­ • Wave measurement system which would en­ + shaper able ground control to drop the bombs Light accurately. Clearly improved accuracy Pulser would be needed, and it was possible that owing to the nature of the system the number of aircraft on the beam at Circular anyone time would be necessarily low. SOkm~ SSkmo ~ t-"''VI--~ scale indiciltor Early Experiments Tone- nerator Meter LlR V-system range-IIIHsurement "electrical H Since the only aircraft receiver avail­ able was the FuG 17 (42 to 48MHz), a multi-beam beacon was designed for it by a Or Herzog of the Gotz Company and given the code-name Wotan 2. A system similar to X-Geriit was also built which used the Bertha 1/-2 televi­ sion transmitter, with similar pulsing and modulation having a dot-dash ratio of 1:7 modulated at 2000Hz. Plendl's analyser was also employed: this system was envisaged as the direc­ V-system rll1gl!-mHSUr-W -mechanicat" tor beam for the aircraft's flightpath. For range-measurement another range") and 3000Hz (equalling 50km, Block diagram of the Y -system special "dash-system" was developed the "fine tuning range") were transmit­ range-measurement systems elec­ at Rechlin. A transmitter tunable ted. Rectifiers loosely coupled to the trical and mechanical between 42 and 48MHz was modulat­ transmitting antennas fed both fre­ ed for 10 seconds at 300Hz, its signal quencies via separate filters and phase being received in the aircraft on a later converters to two small c.r.t.s, to which variation in range was sometimes ob­ mark of Herzog's receiver-now the were also fed the filtered frequencies served, but nevertheless it was of some FuG 17 E and on the German produc­ from the receiver tuned to the aircraft's help when enemy jamming was strong. tion line. Its output was fed through a return signal. Tuning of the phase Later, Or Beller introduced another tone filter and the resulting note modu­ converter resulted in diagonal strokes device known as the "Y-System Mea­ lated an airborne transmitter which . appearing on the screens which served suring Electrical" which was produced returned the signal to the ground on as null-point indicators, and range was by the Graetz Company. A modulation another frequency in the 42 to 48MHz read from a scale marked in note of 300Hz corresponded to 50km, range. There the returned modulation kilometres. but it could also be used for an indica­ note was compared with the original Siemens also produced a range­ tion at, say, 20km and by switching to a one sent from the ground and the measurement known as the Electrical frequency 10 per cent higher the range phase difference, after deduction of the Notebook which recorded the ultimate was extended to 32km, and so on. time lag in the aircraft's equipment, range of five simultaneously measured. Little more, unfortunately, is known gave a direct measure of the range aircraft. This incorporated a fine-mea­ about this method. between the ground transmitter and suring system devised by a Or Beller the aircraft. which used a larger c.r.t. with a circular range-scale showing a range from 0 to . First Trials 20km. A transmitted tone of 7500Hz These systems were, however, only Different Ideas generated a "dark pulse" circular time useful at first for random location: only In fact several systems were tried for zone calibrated against a further circu­ an all-round representation of an air­ the early Y-System, but the one chiefly lar "bright zone", the phase-converted craft was given. For example, the air­ employed was the "Y-Range Measur­ voltage from the receiver being then craft flew to a given point by standard ing System Mechanical" developed by transformed into a pulse which the navigational methods and its range Or H. J. Schmidtmann at Rechlin and electron beam converted into light­ was then measured by these various a Or Jenns of Siemens. Two tone points so that a change in range could electronic systems. Its approach to the frequencies of 300Hz (corresponding be observed directly. This system was point was ascertained by coupling the to 500km, the "coarse measuring . ' somewhat unreliable in that a 5km system to an ultra-short-wave Adcock 30 Practical Wireless, March 1988

www.americanradiohistory.com '-Outward a.am. 2-Retum a.am. t.g.-ton. generator. TX-tran.mit­ ...... , tar. RX-R.c.iver. c.r.t.-c.r.t. with -- ...... , .....g ••c .... Th. runnlng-tlm. in.ide ------~ ------~ the equlpm.nt I ••hown on the .had- '" ..... " • d part. of the graph., the rang.- , ... • cale I. th.r.for. dl.plac.d by thl. ",,,, , valu. on the right-IUInd graph h I I ..... ___ , ,"" ~t H~ l I ...... /i ~-'----~!-'------~~ ~I Ii--=--1 I I 'I 'I'f-.!...-I I I I I Airbornl I I I ! ~ 1 ..,ipMnt I , I ~ ~~! : b: I ~ ~ ~ ~ I lJL'I' I: I T- I \ I \ '1 2 \ I \ , \ :~~~:------~ I :,D_:I : ~ I I I :JL : :: ~~- I ~\~------~I I " I Ground ,I I Iquipllllllt r 'l 1.,- I.... 3f'" , i , , , , , I t.rt I ' • i I , , " o km o km direction finder, code-named Hein­ followed by the cardioid-shaped di­ G.n.rallayout of the Y -.y.t.m with rich. Variants of the earlier X-Gerat poles; this resulted in a slower dot-dash graph. of rang., modulation and system were often incorporated where­ pulse with much shorter gaps at a ratio timing in a director beam was used, but where of 8.8: I, and was acoustically more the old cross beams would have been acceptable. empoyed instead of the X-Uhr com­ In addition, a new receiver based bined clock/calculator would indicate upon Herzog's FuG 17 E was devel­ ous) system of all the German beams the precise timing according to range­ oped by Or H. Oonn and Or W. had it not been for one small item the measurement from the ground. On Hepper and designated the FuG 28a; Germans, in spite of their customary approaching the bomb-release point . manufactured by the Heliowati Com­ thoroughness, had somehow the X-Uhr received a nine-second pany, this was combined into one unit overlooked ... Morse signal and on the last dot the with Plendl's improved AW 28 ana­ bombs were released. lyser. This latter contained a motor Norse Mythology . driving a cam making 180 contacts per minute which conducted the receiver -The Give-Away Final Form output to two series-connected capaci­ As early as June 1940 when Or R. V. Under the direction of Or Plendl a tors: their differential voltages then Jones had final proof of the existence development was devised from this biased the grids of two valves so that of Knickebein he received an Enigma method by Or Herzog in 1940. This one was bridge-switched and a balance decode from Bletchley Park: It is pro­ new system retained the code-name existed if the field strength of the two posed to set up Knickebein and Wotan Wotan 2, the full title of which was the pulses from either transmitter was the installations near Cherbourg and Brest. "Y-Double-Beam Beacon System" and same-that is, if the aircraft was found Wotan was certainly something new, included parts of the multi-beam sys­ on one ofthe two beams. Variation to but what did it mean? He knew that tem already described. left or right gave opposing bridge cur­ Wotan was the greatest of the German Although the same rotating installa­ rents with corresponding responses on gods, but was there anything unusual tion with transmitter and operating the indicating meters. about him-what attributes did he cabin was used, new antennas were The gap between transmissions in possess that moved the Germans to use introduced with seven parallel dipoles each case caused a magnetic coupling his name as a code-word? and reflectors which generated a long between the motor and the switch to Jones phoned his friend Frederick club-shaped lobe with smaller side drop and only to be re-instated when "Bimbo" Norman, Professor of Ger­ lobes. At a half-wavelength in front of the next cycle of transmissions com­ man at King's College, London, then these were two further dipoles spaced menced. In this way a positive synch­ one of the cryptographers at Bletchley at a wavelength apart which, on an ronisation between the ground station Park. ·'Bimbo" was renowned for his opposite phase, produced a "washed and the aircraft was established. To lightning-fast mind and at once gave out" cardioid pattern; thus two sets of position himself on the correct beam proof of it. beams were sent out, one for the the pilot switched on his equipment "Yes, Wotan was the chief German flightpath to the target and the other which also incorporated a sensitive god-wait a moment, he had only one for the aircraft's return. (and heavy duty) relay with an extra eye ... One eye-one beam! Can you Keying the system was originally winding. The relay operated according think of a system that would only use effected by mercury switches or vacu­ to course variations by switching over one beam?" , um relays, but as they gave rise to key­ the polarity for left and right direc­ Or Jones could, in principle; but it clicks they were replaced by the so­ tions: thus the motor would be in the was not until the end of 1940, when X­ called ··capacitive mill" designed by a correct rotation sense when switched Gemt was finally mastered, that he and Or Escherish. This was a motor-driven on until a potentiometer connected his assistant Or F. C. Frank suspected differential capacitor which used a between the motor and the additional that another German beam system light bulb to take the transmitter load winding on the relay delivered suffi­ might be making its appearance. Could between the pauses in transmission. cient voltage to release the relay. this be the Wotan they were looking The long-lobed directional antennas The Y-System could probably have for? The new system seemed to involve were keyed at 176 pulses per minute, been the most effective (if not danger- a director beam plus a means for Practical Wireless, March 1988 31

www.americanradiohistory.com ranging and Jones' suspicions were Bomber ~ aroused when on October 6 an Enigma R --.-.A transmission to what appeared to be a "- station called "Wotan 2" north-west of 42·5HHz ." ",,46'9HHz Cherbourg read: Target No. 1 for "Y" "- co-ordinates 50°41' 49.2N north, 2°14'21.2" west . . 42'5HHz " "" Study of a map revealed these to be " .... the co-ordinates of an army depot at TX " RX k Bovington in Dorset, and they showed RX ..... a great difference from the X-Gerat TX system in which a number of beam directions were always sent out, each (assel Alexandra Palacl station having to set its beam in the The method of interfering with the V -beam system required direction. With this new method, however, the position of the target was given to a single station which suggested that the station had Alrbornl RX and TX with o-,...... A the Plendl Analyslr ~ the entire means of directing the ",k bomber to its target. This seemed to be ",~ confirmed when Bovington was at­ 42'5HHz tacked a few days later by two aircraft with results which, though somewhat inaccurate in direction, were good as regards range.

Frequencies and Ranging principle of the V-system Cyphers Signals Intelligence and our moni­ signed to operate a beam-flying indica­ though not identical, to X-Gerat. But toring services soon began to report the tor in the aircraft. As things turned out, of greater significance was the charred existence of beams on frequencies more surprising developments were to radio operator's notebook: between 40 and SOMHz which had be revealed. very different characteristics from Jones discovered that the aircraft Loge 244 142 10 Knickebein and X-Gerat. Instead of using the new system were not from Schmaistigel 454 149 11 the left and right transmissions being K..Gr.100 but from the Third Group of Bruder 372 120 11 modulated with dots and dashes, the KG 26. He also learned that the scien­ Suden 272 117 11 emissions were of equal duration ex­ tist who had developed the system was BUd 405 137 11 cept for a short pause in transmission none other than Dr Plendl who had when one signal, for example the left, devised X-Gerat. Plendl was the Ger­ Rtick/'hl6 came directly after the pause and the man equivalent ofT. L. Eckersley, our Knowing that KG 26's base was at other signal followed in a sequence leading radio propagation expert, and Poix, south-west of Amiens, and that thus: pause-left, right, pause-left, when Jones asked Eckersley what he "Loge" was the German code-name and so on. thought ofPlendl he replied, "He's not for London, Jones and Charles Frank Dr Robert Cockburn and his assis­ much good, he bases his theory on were able to make the following tants at the Telecommunications Re­ experiment!" interpretation: search Establishment put the signal on (Amateurs please note!) Objective Distance Rhumb Magnetic an oscilloscope and immediately ob­ On 19 January 1941 an aircraft of toPoix Bearing Variation served its principle. The beam emitted KG 26 was shot down and though it loPoix three directional transmissions per was badly damaged it could be seen London 244km 142° 10· second and seemed to have been de- that it carried equipment similar, Sheffield 454km 149° 11" Bristol 372km 120· 11" Southampton 272km 117" 11" Birmingham 405km 137" 11"

Hom~",1lt'd jli6"t The second table in. the notebook gave:

Hinflug 294 10 318 11 283 11 274 11 302 11 By assumimg that these entries re­ ferred to the same cities as those in the first table and that they were bearings, Prof... or R. V. Jones at Clarendon Laboratory, Oxford 1936

Apologies to the inhabitants of Retford, Nottinghamshire, for "relocating" their town in Part 1 of this .erie•. 32 Practical Wireless, March 1988

www.americanradiohistory.com the intersection point appeared to be at Cassel in north France, which gave them:

Outward /light Objective Approach Bearing Magnetic from Cassel Variation London 294 0 lO° Sheffield 3180 1l" Bristol 283 0 11" Southampton 274 0 11" Birmingham 3020 11"

Jones could therefore deduce that: (a) the aircraft approached its target from the direction of Cassel; (b) it was . . i" jI.~2Silj J. ...hodnq,J~

www.americanradiohistory.com by the ground station when to release its Only later did Or Jones learn that also go to AEG (formerly Telefunken) bombs. it had to be monitored all the the Y-System was really Wotan 2. and for their permission to use extracts ,time during its bombing run. and the X-GenU was Wotan 1. "And so, while from Die deutschen Funklenkverfahren ground station could handle only one Wotan may have had one eye for 'Y' he bis 1945, and especially to Dr Colin aircraft at a time. The aircraft would could not have crossed eyes for 'x' .. ." Hamilton, manager of the Airborne therefore fly to a convenient area from In fact the Y -System was nicknamed Early Warning Department, for his which it could be ordered onto the beam "Benito" because Mussolini was consi­ kind assistance and advice. I am also by the ground station. and so com­ dered to be the one-eyed end of the grateful for the help received from mence its bombing run. In principle. all Axis! some old and respected opponents, we needed to do was transmit false So ends the battle of the beams. The notably Herr Fritz Trenkie, author of orders to the aircraft. In fact we did not author hopes that some interest may Die deutschen Funk-Navigations und do this. but it seemed such an easy have been aroused to prompt readers Funk-Filhrungsverfahren bis 1945; Or countermeasure that the German crews to study further this aspect of scientific Rudolph Kllhnhold, designer of the thought we might. and they therefore warfare and to live again those mo­ Freya and Seetakt radars; the late began to be suspicious about the in­ mentous days of the 19405 in the Professor Or Wilhelm T. Runge, de­ structions they received. " company ofsuch distinguished (if then signer of the Mannheim, Darmstadt, Substance was added to this later secret) servants who unravelled the Warzburg and Lichtenstein series of when an aircraft was ordered by the enemy beam systems. radars, who was able to give valuable ground station to steer due west (possi­ But to one man, above all, must go help regarding Telefunken's work in bly because it was east of the beam) to the highest recognition: R. V. Jones, the field of beam systems; and Or bring it onto the start of its bombing the young scientist who defied the Herbert Kiimmritz, Or B. Rode and Or run. Failing to hear further ground experts, confounded officialdom, and Gotthardt Muller. station orders, the aircraft flew a con­ Quietly saved the country from a terri­ siderable distance west then returned ble disaster-yet inexplicably, is still Further Reading to base to complain that the British denied the knighthood he so richly Most Secret War by R. V. Jones. had given false orders. On other occa­ deserves. The man who, to repeat Published by Hamish Hamilton. sions when the power of Alexandra Churchill's words, "Broke the bloody The Bruneval Raid by George Millar. Palace had been increased, aircraft beams." Published by The Bodley Head. became confused and were ordered The Ultra Secret by F. W. Winter­ back to their bases after being told, Acknowledgements botham. Published by Nicolson. again, that a wire was probably loose I am grateful to Professor R. V. The Rise ofthe Boffins by Oark. somewhere in the equipment. "What Jones, Emeritus Professor in the De­ Instruments of Darkness by Alfred with our real countermeasures and partment of Natural Philosophy, Price. those imagined by aircrews. Y-opera­ University of Aberdeen, for his kind For our German speaking readers: tions became a fIaSCO and the system help and advice, and also for his Die deutschen Funk-Navigations und was withdrawn; we had restored our permission to use extracts from his Funk-Fahrungsverfahren bis 1945 by moral ascendency for the rest of the book Most Secret War, published by Fritz Trenkie. Published by Motor­ winter. " Hamish Hamilton. My thanks must buch Verlag.

FRANCE OepARTEMENTS Enclosures Two electronic case ranges, rounded comers throughout. designed for hand-held One model in the range even portables, have been has a moulded pocket clip. launched by West Hyde. The ELOS, whilst being The TINOS and ELOS the more general purpose ranges are available in a total range and without a battery of nine different sizes and in compartment carries, as light grey and black ABS, standard, moulded pads to costing from £ 1.44. provide a base for a p.c.b. The TINOS range have, on and sub-chassis mounting. one side, a textured finish to West Hyde Developments. provide a firmer grip, also a 9-10 Part St. Ind. Est•• battery compartment for Aylesbury. PP3 9V batteries and Bucks HP20 1ET. Dlplomedu RTTY, etc., on request. Calvados Contact with the club The REF regional club of the station, FF6KCZ on h.f. or Department du Calvados in FF1KCZ on v.h.f. counts as Normandy, have an award two contacts. available to all radio No QSLs are necessary, amateurs and s.w.l.s. send your log details, Applicants must have certified by two licensed worked (or heard) 10 amateurs and 10 IRCs to: stations located in the The Award Manager. Calvados district (No. 14) on Pierre Roger FC 1CNJ. any band and/or mode. B Rue des Petites Haies. There are special F. 14440 Oouvres La endorsements available for Oelivrande, h.f., v.h.f., s.h.f., C.w., France. 34 Practical Wireless, March 1988

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