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 Regular Features 79 Advert Index 16 News Desk 38 Short Wave 33 Binders 64 On the Air Magazine 56 Book Service 47 PCB Service 58 Subscriptions 12 Comment 14 PW Services 12 Write On Editorial and Advertisement Offices: Editor Geoff Arnold T .Eng FSERT G3GSR Practical Wireless Assistant Editor Dick Ganderton C.Eng . MIERE G8VFH Enefco House Art Editor Steve Hunt The Quay Technical Features Editor Elaine Richards G4LFM Poole, Dorset BH 15 1PP Technical Projects Sub-Editor Richard Ayley 'S' Poole (0202) 678558 (Out-of-hours service by answering machine) Editorial Assistant Sharon George Prestel202671191 Technical Artist Rob Mackie Administration Manager Kathy Etheridge Advertisement Manager Clerical Assistant Claire Horton RogerHaIlG4TNT'S'01-7316222 COPYRIGHT © P'W Publishing Limiterl 1988. Copyright in all drawings, photographs, and articles publisherl in Practical Wireless is fully protecterl and reproduction or imitation in whole or in part is expressly forbidden . All reasonable precautions are taken by Practical Wireless to ensure that the advice and data given to our readers are reliable. We cannot however guarantee it and we cannot accept legal responsibility for it. Prices are those current as we go to press. Practical Wireless, January 1988 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.