Two New Multiband Trap W8NX details ai new coax trap design used in two multiband antennas; one covering 80,40,20, 15 and 10 meters, and the other covering 80, 40, 17 and 12 meters.

Over the lasi 60 or 7 0 yearr, amateurs hnçe uscd many kinds of multilrand antennas rn çover the traditional H F handr. The availability of ihe 30. 17 antl 12-meter

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with rimplc aniennas cnntiniie~. At the end o f rhc 19?0q,3 different technolopical approach appcared i n ihe fvrm of resoiinni trnps i n 111tennm. Thc Minrs S i g nnl Sqiri-ter is the ~ r a n d f a t h c rof modem day t r i h a n d c r ~ .'This ~ anicle discuï.;es i n detnil an innovativc trnp d e ~ i g neniploycd

bandqhas tirpandcd a u r need fnr moltihand :menna covcrage. A feriunatc few have the qpnce and SÇF(III;CCF for rniilt i band aniennas Irke rhombicr o r long V s , but many i n iwo muliihand rlrpnle~ ham. have crnploycd invcrred-L long wires or parallcl dtpoles. Old-timcrq wrll rccalr One W8UX Trap Deslgn-Two the offcenier-fed IVindnrn of thc '30s-t he Mul tlband Dipores T w o diffcreni 3ntcnnos arc descrihcd ftrqt version usinR a s i n ~ l c - w i r etranqrntqsion Iiiie. and the laier d c s i ~ n itsing here. The Tir-ïi cnvcrq 80, dO,?O. 15 and ltl IWO-wirefeed line. Over the yenrs. random- meicrs. and the scconrl coverq 80. 40. 17 lenpih dipolcs with open-wire fecder5 and and 12 merers. Each USCF rhr urne ~ y p cof assoçiated tuners Iiave h ~ c niiscd successW8NX ~r;ip+nnnectcd for difrerenr fu31y as multibanr'l antcnnas. The G 5 R Y rnodcc of operatinn-and a pair c i f short camultiband nntcnnaisa spcciali7cd example pacitive stuhs IR enhance coifersFe. Thc of th?\ approach.' n e w WRNX coaxial-cable rrnps have two Rit Iri~~~eriodicnrrrir reprrrxentsnliind different modes: ir higli- and a Iow-impedof hruit-f'nrcc approach to tlic goal o f ancc mode. The inner-condiictor windings achicvin_e coverape of multiple HF ham and shield wlndinps o f the irnps arc çonbandr. I i sccms ~nçffiçienrbecause of the necrcd in series III rhc conveiiirtinal rnanner large gaps hetween our rc!ativcly nnrrow amarcitr HF bands. Occr ihe last few dccades. two f ~ ç f o r ~ hzvc üffecrcd t h e dcve!opment of rnliltiband ~nrennas-the poptilarity of Iow-impedancc 4 usually 50-01çoaxia! feed IInes, nnd thc nppcarance of uiituned, 50-11 FOI rdstnic arnplafierc. The impetlance o f ari anienna i s rclativcly low ocly *II its fiinda-

mental frequencv and a t odd-order harnicanics. A l t h o i i ~ hnntenna tuners nrr ofwn

necersnrv 10 rcsrinate an nntennn syqtcm. the queszfotcnparded muliihand coveraEe

for hnth niode\ H O U P L P ~e .i ~ h e rihc liiw or high-irnpedrtnçe point can hc iisetl a $ the itap.5 u i i t ~ u terminal. i For low-impcd:i.rcc irap operaiion. nnlj the cenret contiucirir iurn\ of rlic triip winrling< arc uscii For high-impednncc operazion. a!! i u r n \ arc uscd. in ilie convcniioii;il rniiiincr tora i n p The çhon r i ~ i h con esch .inrenn> are ktr:!i gically sirrd ancl localcd in perrnin mhrc flertFi1iiy i n ad~iirtincthe scynnant frequcncies O!+ the antcnn.1 Figure 1 ïhnwc the confijiur:ilion nf ihe SO, JO. ?O. 1,i and 10-meier antinna Thc radi:iiinp clernrtits arc mntle r i ! # l J sirandtd ccipprr w i r r 'I'lie rPcmcnt leng:h~ are bhe w i r r spnn l e n p i h ~in fecr 'i'hcrc Icnpths do not includc the Irnpths of rlrr p i ~ r a t Ja!~ the balun. traps ~ i i in5tilsrnr. d Vif 32.3-fnot-long inncr 40-metcr q e p rn-nlc arc rneasiired :'rom rhc rveYci (il thc rnpiii bnlun ID the icneinn relicC holc i n thc rrayicoil f n m T h î J.9-foot segrneni leneth is ~ r i e n ~ u r clrniii d rhe icnçjnn r ~ l i c fholc i n

Point

123 RF

Figure 1-4 W8NX muIliband dipole lar 80,40, 20,15 and 10 meters. The values shown (123 pF and 4 1iH) for the coaxial-cabre iraps are lor parallel resonarice a: 7 15 MHz. The low-impedance output ol each trap is used For lhts a n t e n n ~

Çhapter 3

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