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Radar System Engineering

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478 THE RECEI VI.YG SYJSTEM-1.VDICA TORS [SEC.13.1<br />

iron-cored coils for this purpose are sketched in Fig. 13.2 and pictured in<br />

Fig. 13.3. Care must be taken that surrounding fixed objects do not<br />

introduce a lack of rotational symmetry and that no magnetizable<br />

material is included in the rotating parts.<br />

Multiple coils are used for many different purposes. Their fields<br />

must occupy the same axial region of the tube in order to avoid serious<br />

defocusing and distortion which otherwise take place when deflections<br />

1)<br />

(g)<br />

,,,<br />

l’1 dc.fle,tion coil. (c, .Ii, -cure deflection (coil for<br />

off-center PPI, u.cd in e,J[liwl[tion ~!ith (:l],cnt-r,lagnct focu>ing unit. c; l’orll.ing ?uil.<br />

of appreci:~hle maguit udc are combiuccl. In some applications reqllh-iug<br />

a fixed component of field, a perman{’nt mngnet is IIMT1 in Ii?u (of 3 coil.<br />

Often coils are arranged orthogonally (I~ig. 133) either to produce<br />

entirely indepcndrnt dcfkctions (w in z t~qm B displ:~}-’). or to pro~-idc a<br />

single radial ckflcction (such as a range m~-eep~LJ-addin~ its two rectangular<br />

components ~-ectoriall~-. The latter tt,chniquc is l~sed in the RH1, the<br />

fixed-coil PPI, and in other applications.<br />

It is somctimw neceswr~” to add dissimilar deflections in the s~me<br />

,lirection. ll-henc~-er practiralj this i+ done by achling the ~-ariou~<br />

deflecting currents in the same coil. Tn some cases. howc~cr, this is

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