FEBRUARY 1938 59

A ROTATING DIRECTIONAL AERIAL FOR SHORT ,WAVE;, BROADÇASTING

by.P, J. 'H. A. NORDLOHNE.

A description is given of the rotating direction'1l1aerial erected at Huizen for broadcastingfro:m:the transmitter' PCJ· on 31.28 m. ' .

On November 16th 1937 a rotating directionalaerialwas put into use at Huizen for experimentaltransmission by the short wave station PCJ des-'cribed in' the previous number, with' a frequencyof 9.59 megacycles (wave len,gth 3~:?8, m):"Thisdirectional aerial was designed" for a power ofabout 75 kW carrier wave energy.

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25221Fig. 1.. View from above of a uni-directional "aerial.

The purpose: of building a rotating aerial was tomake possible _the \ restrietion of the energy toany chosen direction with a single aerial: instal- 'lation, and in this way to concentrate all the avail-able energy toward a given part of the world, forexample toward a given part of North, CentralorSouth America: "

Instead of a rotating aerial, up to now it has beenusual to build a number of permanent fixed direc-tional aerials for this purpose; each of which servedfor a single definite direction. The angle of emergence

25222

Fig. 2. Position of the half wave aerial 'wires in the verticalplane.

621.396.677.029.58

_ofthe .beam sent out by' a directional aerial can bechosen' more or less, wide. If aerials with smallangles of emergence are built, a' narrower sectionof the earth's surface is reached; but with greaterintensity; .if, on the other hand, the aerials havelarge angles .of emergence à' wider section of theearth's surface 'is covered, bilt' at th~ cost of inten-sity.

Considering the fact that the wave length withwhich one seJÇvesa certain distant part of the worldis almost always less suitable for another" distantpart of. the world in the opposite direction, since,for examplc.ithe state of ionization along the path.to the latter is different, it is advantageous to make"the directional effect ofthe aerial one-sided. Thusthe aerial m u s t no t i~d tat e a n-y ene r gyin

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Fig. 3. View from above of the towers with the aerial wireshung on the projecting supports.

a backwards d ir ec t ion, This uni-directional.action can be attained by grouping the variousaerial wires in two parallel planes 'which lie at adistance of a quarter wave length from each other,and by giving the currents in front and rear planesa phase difference of 90°.

, ~Fig. 1gives a .view ~f the uni-directional aèriai. from above. The supply is such that the currentsin the aerial wires 'öf the front plane are ."90° inphase behind those .of the wires of the rear plane,SO" that the. waves which the two' planes radiate,~\'heÎl they hav~ the same amplitude, 'will reinforceeach other toward the front and exactly neutralizeeach other toward the back., The sharpness of the beam depends' upon thenumber 'of ~erial wires next to each other in eachplane and on the mutU:al separation of thewires. Ifdirectional ~eri"iilsfor a given frequency are avail-able, the intensity of which falls to one half at13° on either side of the main direction, and if it isdesired to reach all parts of the world from EastAfrica to and including the United States with an

60 PHILIPS TECHNICAL REVIEW Vol. 3, No. 2

intensity which is never less than half of that inthe main direction of the aerial, eight such aerialswould be necessary. These directional aerialsshould be placed along the sides of a polygon toprevent one aerial from exerting too much in-fluence on the radiation diagram of another, Thetransmitter building may be situated at the centreof the circumscribed circle of the polygon. Withthis method very large areas of ground are neces-sary, as well as one or more complicated and ex-pensive switching arrangements.These objections are avoided with the rotating

aerial.For the rotating aerial of PC] for a wave length

of 31.28 m two 60 m wooden towers were builtwhich can rotate together around a central pivot.In connection with the desired concentration ofradiant energy in a horizontal as well as in verticalplane, four aerial wires a half wave in length weresuspended next to each other, and three were sus-pended one above the other in the same verticalplane (fig. 2), while two of such planes were placedone behind the other as shown in fig. 1. These aerialwires may be hung in the usual way between thetwo towel's, but in that case the diameter of thecircle described by the rotating towers is relativelylarge. When steel masts are used, moreover, inorder to limit the currents induced in them, whichwould have an undesirable influence on the radiation

Fig. 4. Wheel boxes on the outer track.

Fig. 5. Anchorage of the steel pivot about which the wholerotating aerial is centred.

pattern, the distance from the aerials to the poleswould have to be made equal to at least about onewave length, so that the structure would be un-reasonably large. The diameter of the circle des-cribed can be considerably decreased by usingwoo den towers and by not suspending the aerialsbetween them, but on the towers themselves. Inthis case the towers must be provided with projee-ting supports in the form of platforms (fig. 3).Each tower then carries four vertical wires, eachof which is divided by two insulators into threehalf wave aerials whose currents are in phase witheach other. Since the distance between the aerialsin the front as well as the rear plane is fixedat a half wave length, the distance between thecentres of the towers becomes exactly one wavelength.

In order to allow the whole structure to rotateeasily, the two towers must be joined together attheir bases. They must therefore be mounted in thesame rotating undercarriage. The latter consists ofa steel construction about 54 by 13 m which restsat each of the eight points where it bears thetowers on a set of wheels (fig. 4) consisting oftwo wheels in a line (16 wheels in all). Four ofthese sets of wheels are on the outer track, the

FEBRUARY 1938 ROTATING DIRECTIONAL AERIAL FOR SHORT WAVES

other four on the inner track. The outer track hasa diameter of about 46.4 m and consists of a normalrail AH no. 1, welded to an I-girder, DIN 24,which in turn is anchored in a (circular) wall ofreinforced concrete. The inner track is constructedin exactly the same way but has a diameter ofabout 22.4 m.

Since during rotation in a strong wind thewheels might be pressed against the sides of the

the steel framework weighs about 40 tons, whileeach set of wheels weighs 1.5 tons.The wheels rotate on double ball bearings. There

is one set of wheels under each of the four postsof the two towers.The heaviest load occurs as the result of a wind

diagonally against the towers. There is then a38 ton compressive stress on one side and a 38 tontensile stress on the other side. In this way a

Fig. 6. The wooden towers of the rotating aerial.

rails, the whole structure is centred about a steelpivot which is anchored in a block of reinforcedconcrete with a heavy base (fig. 5). This pivottherefore serves exclusively to take up the horizon-tal forces.

The wooden towers are made of Norwegian firimpregnated with a substance to prevent rot. Thegeneral construction can be seen clearly in fig. 6.All joints are made with nuts and bolts, whileseveral important points are provided with ironbutt straps. Each wooden tower weighs 18 tons,

maximum load of 51 tons may occur on one set ofwheels: 4.5 tons from the wooden tower, 7 tonsfrom the steel undercarriage, 1.5 tons from thewheels themselves and 38 tons due to the force ofthe wind. In the construction of the towers thecalculations were made, according to the Nether-lands Normalization Committee, with a wind forceof 70 kgjm2 for the first 20 m of height, while forevery additional meter of height an increase ofpressure of 1.5 kgjm2 is calculated. This increase,however, goes only to a height of 40m, so that above

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62 PHILlPS TECHNICAL REVIEW Vol. 3, No. 2

this height the pressure remams 100 kg/m2. Thewind pressure makes heavy demands on the woodconstruction, considering the fact that the surfaceon which the wind exerts its force is much greater"than that of an iron tower, which can always beconstructed in a more slender form. Moreover, theplatforms in the shape of a cross, on whose extrem-ities the aerial wires are hung, represent loadswhich are effective at the top, and thus make largecontributions to the moment of the forces actingon the tower.The construction of a tower was carried out m

Fig. 7. The bridge with the towers is freed from the concreteblocks and rests upon the wheels.

the following way. Two sides about 20 m high werefirst built on the ground. After thcse had beenerected in their places the necessary struts etc.were added to complete the other two sides. Thetower was finished with the help of a hoist andtackle and temporary scaffolding.The iron framework was also made ready in large

sections which were put together on the spot.The specially constructed wheels are mounted inpractically closed long narrow boxes (cf. fig. 4).Since the wheels could not be delivered quicklyenough, and it was impossible to wait for thembecause of the lateness of the season, the framework

and towers were first mounted on eight concreteblocks. It was then possible, during the construc-tion of the towers and the putting together of the

Fig. 8. Diagram of the supply of the aerial. The aerial can befed from 0 via, Hl or H2 to M.

framework, to level the ground, cast the concretewalls for the tracks and to fix the I-girders andfinally the rails.

The last eperation was that of fastening the wheelboxes underneath the framework, and then freeingthe connection between the framework and theeight concrete blocks (fig. 7). During this operatienthe framework was supported by jacks. The wholewas easily lowered a distance of 0.5 cm on to therails.

Rotation, is, for the time being, carried out by hand,

25225

Fig. 9. Diagram showing supply circuit whim using the supplyarm AIA2' via H2 or H2 from O.

FEBRUARY 1938 ROTATING DIRECTIONAL AERIAL FOR SHORT WAVES

for which purpose two hand capstans are fastenedunderneath the framework. From each capstan asteel cahle passes to a single pulley block which isfastened to a shoe on the outer rail, and from thereto one of the wheel boxes. Two men at each capstancan easily set the towers in motion, while the motioncan be maintained with one or two men.' An elec-trical drive is now being designed, about whichwe cannot yet give any details.

The energy is supplied to the aerial verticallyabove the .pivot by means of overhead connections.With a permanent, fixed supply connectionthere would be certain positions of the tower atwhich they would touch the supply lines or thelatter would have to be conducted through thetowers. By arranging the supply from two pointsthis difficulty is avoided (fig. 8). In order to changefrom the supply point HI to the point H2 theswitch at 0 must be reversed and the supply lineMHI is replaced by MH2•

Changing the supply line is rather time-consuming,and in the long run a troublesome operation. Forthis reason a rotating supply arm has been designed,which can rotate independently of the towers on apivot of its own above the framework pivot andwhich rests on the track. From the position drawnin fig. 9 the towers can then be turned to the rightover about. 1000 without the necessity of any com-mutation. With a greater rotation than this, theaerials must be supplied via H2 by means of theother half of the rotating arm. For this purposethe switch at 0 must be reversed, the switch at HIopened and the rotating arm turned to the rightuntil A2 reaches Hz. The switch at H2 can then beclosed. Fig. 10 gives a view of the Phohi groundsat Huizen where the PHI transmit.t crs of thePhohi and the PC] transmitter are set up. Thenew rotating directional aerial which serves forbroadcasting on 31.28 m may clearly bc seen atthe left. In the centre background is the permanent

Fig. 10. General view of the grounds of the PHI transmitters of the Phohi and PCJ.

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64 PHILIPS TECHNICAL REVIEW Vol. ,3, No. 2

directional aerial-used up to now for experimentalbroadcasting by PCJ on 19.71 m to the Dutch EastIndies and British India. At the top of the woodenpole of this fixed directional aerial is a dipoleaerial for non-directional broadcasting on either19.71 or 31.28 m. To the right between the two

•high towers hangs the fixed directional aerial ofthe Phohi' transmitter for broadcasting to the DutchEast Indies on a wave length of 16.88 m. Under thetower to the right, in the background, may be seenthe fixed permanent aerial fo~ transmission on awave length of 25.37 m to' the Dutch East Indies.

•

ABSTRACTS.OF REC~NT SCIENTIFIC.PUBLICATIONS OF THEN.V. PHILIPS', GLOEILAMPÉNFABRIEKEN

1247*: J. van Niekerk: Anaphylaxie und Vita-min C (Act. brevia Neerl. 7, 144 - 146,1937).

Compare 1238 for the investigations describedin this article.

1248: J. H. de Boer and E. J. W. Verwey:Semi-conductors with partially and com-pletely filled 3d lattice bands (Proc. phys.Soc. 49, extra ;part, 59 - 71, Aug. 1937.

Semi-conductors and insulators ate disèussed withincompletely filled bands of the energy levels of 3delectrons. Ifthey possess a.whole number of electronsper atom their lack of conductivity may be explained

. by the very great probability that the movingelectron will be drawn back by its original atom,if only the potential h~rriers to be passed through- are great enough to keep the probability of transitionsufficiently small. If the number of elect~ons peratom of a definite level is not a whole number thehindrance to I conduction disappears. This is thecase for example in lattices of Fea04 and nickelor copper oxide when some of the places of the.metal ions are unoccupied.

Substances with completely filled energy bandsmay be~ome conductive as a result of irradiationwith light which is capable of raising electrons intoa band of higher energy. If several' oxygen placesin a zinc oxide lattice are empty, the excess electronin the lattice will he able to change the Zn+ + ionsinto Zn++ ions by passing over into the energyband of'-the 4 a-electrons.

1249*: M. J. O. Stru tt: Moderne Mehrgitter-

*) An' adequate number of reprints for the purpose of dis-tribution is not available of those publications marked withan asterisk. Reprints of other publications may be obtainedon application to the Natuurkundig Laboratorium, N.V.Philips' Gloeilampenfabrieken; Eindhoven, (Holland),Kastanjelaan.

Elektronenröhren, Erster Band: Bau,Arbeitsweise, Eigenschaften (138 pages;Julius Springer, Berlin 1937).

In à comprehensible but not too elementary waythis book gives the basis of. the development ofradio valves with several grids. The direct stimulusto the preparation of this book was the lecture

. mentioned in 1148 before the Physikalische Gesell-schaft Zürich.

1250: Balth. van der Pol: Television (Natuurk.,voordracht Mij. Diligentia, The Hague, 15,36 - 45, Oct. 1937).

In this Diligentia lecture a survey was given ofthe present position of television. The relation toother ,subjects of research, such as relaxationoscillations and the theory of the rainbow waspointed out among other features.

In Nov. 1937 appeared:

Philips Transmitting News 4, No. 5:

.J. P. Heyboer: The use of pentodes in radio-transmitters (continuation}. .Studio-equipmentfor League of Nations - Geneva.

M. J. Druyvesteyn and. J. G. W. Mulder:Physical principles of gasfilled hot-cathode recti-~n. '

,In Dec. 1937 appeared:

Philips Transmitting News 4, No. 6:

J. P. Heyboer: The use of -pentodes ill radio-transmitters (continuation].A rotabie directional aerial for short wave worldbroadcasting.

P. Zijlstra: The Philips ultra short wave radiobeacon type B.R.A. 075/4: