A multi-band inverted-v dipole for portable operation PART ONE

Transcription

1 Anré Suners, GM3VLB TECHNICAL FEATURE 6 Dougls Cresent, Kelso, Roxurghshire TD5 8BB. A multi-n inverte-v ipole for portle opertion PART ONE t the time of writing, the uthor h tivte 148 islns, 136 of A these in the lst eight yers for the SCOTIA (n IOSA) Sottish isln wr progrmmes (for further informtion, see his wesite Operting time is generlly limite, with most opertions (mny of whih hve een solo ) eing of 1 or 2 ys urtion. The mjority of Sottish islns re uninhite, n often inhospitle. Lnings my hve to tke ple in strong Atlnti swell, n from very smll rft suh s inghy or RIB. ( rigi infltle ). The time-onsuming ssemly of omplex rotry ems hs heretofore never een onsiere. Likewise, ny mplifier woul neessitte oth lrger n hevier genertor n more fuel. Even if use in onjuntion with em, suh setup woul e unlikely to give more thn few B gin over the Kenwoo TS-50S running 100W into well-mthe inverte-v ner the se. In prtie, it hs een foun tht 50W ( 1 / 2 n S- point less t the reeiving en!) is frequently equte. Inee, given resonle onitions n split opertion, the use of QRP is perfetly vile option. All Sottish isln opertions hve use one or more of either short, loe fishing-ro vertils or inverte-v multi-n ipoles. This rtile looks more losely t the ltter. The prinipl vntge of the inverte-v ipole is tht it requires only one, entrl, support. The min mst use y the uthor is ex-rmy n omes in onvenient shouler g ontining eight 1m long fireglss poles, two sets of guys (three t RCom Mrh 2005 Operting /P on the isln of Killegry, Outer Heries. In this first prt of two-prt rtile, GM3VLB esries one of his ltest esigns, whih hs een trie n teste. the entre n three t the top) n simple pulley system (n ultr-lightweight version using roh pole hs lso een onstrute). The mst is esily erete y one person, even in howling Herien gle, n supports the ntenn, whih ts s resonnt λ/2 inverte-v ipole on eh of the 20m, 40m n 80m ns. The ntenn n lso e use on the 15m n, where it ehves s 3λ/2 ipole (3λ/2 mens one n hlf wvelengths MHz is 3 x 7.050MHz, so λ/2 on 40m is 3λ/2 on 15m. A seon, lighter, multi-n inverte-v overing 10m, 12m, 15m, 17m (n 30m with en extensions) supporte t out 7m y roh pole, is lso ville. (The uthor hs reently teste nother esign of the sme overll length s the 20/40/80m version, ut with slightly ifferent onfigurtion n in whih the 20m ipole is 3λ/2 long, giving smll, though useful gin on this n n with two itionl min loes, giving inrese glol overge - see the Appenix next month for etils. As stte ove, these ntenns re omplemente y vriety of multin vertils, most of whih n lso e use /M on islns with vehiulr ess. BASIC DESIGN CONSIDERATIONS The multi-n ipole is set-up in inverte-v onfigurtion, ie the entrl fee-point is t the pex of the Λ t the top of the mst, with the two hlves sloping own to points out 60m (2ft) ove the groun. On 20m n 40m, it is esigne to e resonnt mi-wy etween the IOTA CW n SSB frequenies generlly fvoure y isln opertors n (orresponing in this se to MHz n 7.050MHz). On 80m, the esign frequeny is 3.772MHz. A swithe liner lun trnsformer t the feepoint (giving hoie of two rtios, either 1:1 or 2.25:1) llows impene mthing s well s unlne oxto-lne ipole opertion. The fee-line onsists of 3.6m length of 50Ω RG-58 ox (75Ω ox ws use, unwittingly, for severl yers - see elow). This is veloity ftor-orrete hlf-wvelength on 40m, two hlf-wvelengths on 20m n three on 15m. On these ns, the ox simply reflets the impene t the lo en in this se, the input to the lun. On 15m, 20m n 40m, this is resonly lose to 50Ω, thus proviing goo mth to 50Ω ox n thene to the TS-50S. On 80m, t height of only 8m (0.1λ), the textooks woul suggest n input impene of only few ohms. In prtie, it woul seem to e quite it higher, n n pproh 50Ω. However, t the time of the erly experiments, the uthor i not possess n ntenn nlyser. A lower vlue of roun 20Ω ws therefore ssume (h the physis teher not repetely si Never ssume nything oy!?). A 2.25:1 lun ws esigne to rise this to nerer 50Ω to provie etter mth for the ox n the TS-50S. When the system ws teste using this lun, the VVSWR ws, inee, s preite. Swithing over to the 1:1 lun resulte in n unusle VSWR! All worke perfetly - exept the mths! One y, some yers lter on the isln of Rum, ox fult ourre. The spre ox ws instlle. Result? High VSWR on 80m! With the help of isln prtner Alex, GM0DHZ, n whilst ttling the most intense infesttion of miges ever experiene, everything ws trie n teste to no vil. Lter, whilst repiring the fulty ox, it ws notie to e of slightly lrger imeter. It h een me from length of RG-59 slvge from the uthor s 5Z4 ys in the π-output 1960s! It ws 75Ω ox n not 50Ω s originlly thought! So why i it work? Well, it s mzing how you n prove something with the wrong mthemtis! Now, y working kwrs, n pplying wht ws elieve to e the orret qurter-wve trnsformer formul, ut the terms of whih h een invertently trnspose, the tul ntenn impene h een prove to e 33.75Ω this h seeme entirely resonle! In ft, no-one h hllenge this proof until few weeks go when Dle, WB6BYU, in Oregon e-mile me sying (ever so iplomtilly!): You re wrong mte! The formul shoul e: Z? ox = Z lo x Z rig. If we gin work kwrs using Z rig = 50Ω n Z ox = 75Ω, we get 85

2 FIG 1 RADCOM 432 FIG 2 RADCOM 433 Trnseiver Antenn 200pF 200pF 1:1 2.25:1 L 1 6t L 2 40t 1 pole 12 wy Blne Trnseiver (unlne) X Y Z lo = 112.5Ω. Rememering our 2.25:1 lun, the ntenn input impene must in ft e 112.5/2.25 = 50Ω! WB6BYU si tht his own experiments inite the input impene ws nerer this vlue n, if this ws the se, ll tht ws require ws to use the 1:1 lun n 50Ω ox! This, in ft, is the se! This just shows tht you shouln t lwys elieve wht you re! Thnks, Dle ATU OR NO ATU? Clerly, the ntenn system is resonnt n mthe n n ATU is therefore not normlly require on ny of these ns (ie 15m, 20m, 40m or 80m).The uthor is silly nti-atu, ut oes rry very smll homerew T-mth ATU onsisting of two 200pF semi-vrile pitors, moifie to hve shft, n swithe 40-turn toroi + 6- turn fixe oil ssemly this is primrily use to twek the GM3VLB multi-n fishing ro vertils whih re lso essentilly resonnt. See the ATU photogrph. Detils of the ATU Referring to Fig 1: L1: 25mm imeter, 6t of 16SWG tppe t 2, 4 n 6 turns. L2: T130-2 toroil ore, 40t of 18SWG, tppe t 2, 4, 7, 10, 14, 19, 25, 32 n 40 turns. NB: Do not e tempte to onnet x to y s this retes shorte turns whih re not permissile when using toroil ores. Fig 1: Ciruit of the mini-atu. Detils: L1: 25mm imeter, 6 turns / 16SWG tppe t 2, 4 & 6 turns. L2: T130-2 toroil ore, 40 turns / 18 SWG tppe t 2, 4, 7, 10, 14, 19, 25, 32 & 40 turns. NB: Do not e tempte to onnet X to Y s this retes shorte turns whih re not permissile when using toroil ores. Fig 2: Wiring etils of the qurifilr ulrtio lun. Fig 3: Construtionl etils of the lun. Fig 4: Detils of the ntenn. Fig 5: Insultor onstrution. Right, top: The mini- ATU. Right, mile: The swithe ul-rtio lun. Right, ottom: One of the insultors. CONSTRUCTION OF THE BALUN Although now superfluous, the esign n the onstrution etils for the ul-rtio lun re inlue, s it my prove useful essory when ttempting to mth other lne ntenns. It is uilt into stnr 75 x 50 x 25mm ABS ox (see igrms n the photogrph). Three eyes re srewe into piee of thik (7 or 8mm) plsti in the top hlf of the ox. One eye is for the pulley, n the other two for the ipole legs. The ox ontins the swithe lun, onsisting of qurifilr wining on ferrite ro pproximtely 6m long, SPDT miniture toggle swith n BNC soket with wether shiel (the uthor uses plsti ottle top). Brss olts with wing nuts protrue through the k of the ox to ept the spe ens of the ipole. Insie the ox, the onnetions re solere to the hes of the olts to reue the risk of orrosion n/or poor ontts. Wining the Blun Fig 2 shows the iruit igrm of the ul-rtio lun, n Fig 3 the onstrutionl etils. Streth four 45m lengths of enmelle 20 or 22SWG opper wire from vie to remove ny kinks. (ifferent olours re iel). Twist these together out eight times. Win eight turns onto 10mm imeter ferrite ro, out 6m long (perhps slvge from trnsistor rio?), holing the ens in ple with tie-wrps (for exmple). With tg-strip fixe to the ens on the winings (not shown), use further enmelle wire to mke three links etween n, 1 n, n 1 n (mke these links s short s possile). All links n joints shoul e solere o not rely on purely mehnil onnetions. Constrution of the ipole legs There re two insultors (see the photogrph n Fig 4) on eh leg, me from suitle plsti (test in mirowve oven first!) out 60 x 20 x 5mm, eh with hole t eh en to tke smll S-hook tthe to the smll strin-relieving thimles (Fig 5) t the ens of eh element. A entrl rss olt n wing nut llows prtiulr element to e onnete or not ( plug n soket rrngement, or 1 / 4 in spe onnetors oul lso e use). The lower ens of the 20m n 40m elements re solere to the hes of the olts whilst the upper ens of the 40m n 80m elements hve 13 15m tils with U-shpe tgs to fit uner the wing-nuts. The thimles n e pro- FIG :1 1:1 Trnseiver (unlne) RADCOM 434 Blne 86 Mrh 2005 RCom

3 FIG 3 RADCOM 435 Eyes FIG 4 RADCOM 436 Blun ABS ox 75x50x25mm 20m I 1 Insultors 40m I 2 80m I 1 n I 2 oth shorte for 80m (only I 1 shorte for 40m) just 1 8x1m 1 1 FIG 5 RADCOM 437 4x8t Preferly rss olt n wing-nut 'Tils' out m Ferrite ro BNC Bottle p SPDT 1:1 2.25:1 S-hooks fessionl, metl or plsti, or n e otherwise improvise. Bn hnging is simple simply lower the ipole, isonnet the unwnte segment(s) n hoist the eril up gin - two minutes t most! x 60 x 20 x 5 mm plsti x: soler tg - lso solere to the nut Thimles NEXT TIME GM3VLB looks t the numers ehin the esign, the nture of the groun n the height of the ntenn ens ove it. Dimensions re given for the ns in use. UK Stokist for the ECOFLEX Rnge of les n onnetors Airell 7 7mmø UltrFlexi ox 1p/m or m Drum Eoflex 10 UltrFlexi LOW LOSS 1.40p/m/ m Drum Eoflex 15Ultr Low Loss & Flexi 0-25m = 2.85p/m ½ inh 50R oxil Cle 26-50m = 2.75p/m 51-75m = 2.70p/m 100m DRUMS = 265 RG174 Mil-C-17 spe minture ox 50R...30p/m Single ore Auio le with sreen...30p/m 4 Core with lppe sreen...45p/m 7 Core Hevy Duty Rottor Cle...70p/m CONNECTORS UHF/PL259 7mm Pxoline Insultor...85p UHF/PL259 7mm Teflon insultor Gol Pin UHF/PL259 7mm Teflon with Gol Pin CLAMP FIT UHF/PL259 Pxoline Insultor Lrge le (10mm)...80p UHF/PL259 Teflon/Gol Pin CLAMP FIT Eo10/W N-Plug Eoflex10/W103/LMR400 CLAMP FIT N-Plug Airell7 n other 7mm les N-Plug SolerLess Eoflex15 NO SPECIAL TOOLS!!! Plese go to the wesite or ll for ll the prouts tht we sell too mny to list here. WEBSITE sles@ioeomms.o.uk Tel/Fx RCom Mrh

4 Anré Suners, GM3VLB 6 Dougls Cresent, Kelso, Roxurghshire TD5 8BB. A multi-n inverte-v ipole for portle opertion PART TWO B efore giving the imensions for the inverte-v, here re some funmentl onsiertions. (1) Length of λ/2 ipole Reers will e fmilir with the following rule of thum formule whih pply to horizontl ipoles either in free spe or t lest hlf-wvelength ove groun. If f is the esign resonnt frequeny in MHz, we hve the sitution represente y Eqution 1. In prtie, the length is shorter thn this ue to the so-lle eneffet of the insultors n their supports. Eqution 2 gives the physil sitution. Eh leg of λ/2 horizontl ipole is thus hlf of this, or 71/f metres long. For exmple, for λ/2 ipole resonnt on or out MHz, the length of eh will e 71/14.15 or 5.02m (16ft 5in). This is out 0.95 of the free-spe length of 5.30m (17ft 5in). Thus, the reltion of the physil n free-spe lengths re relte y Eqution 3. However, wht is generlly not me ler in the literture is tht, s the ens re lowere towrs the groun into wht is known s inverte-v onfigurtion, the reso- Eqution 1 Eqution 2 Eqution 3 Eqution 4 Eqution 5 In this onluing prt of two-prt rtile, GM3VLB onsiers the imensions of his inverte-v for severl ns. nnt frequeny rops the ntenn eomes too long! To mintin the originl resonnt frequeny, the length of the inverte-v must therefore e reue. This is proly the use of muh he srthing when trying to tune inverte-vs. The uthor s experiments on inverte-v ipoles suggest the empiril formul given in Eqution 4. It is regrettle tht the literture oes not mke this ler. (2) Effet of height of the ens ove groun The ove figures re not st in stone. They re very muh epenent on the resonnt frequenies hosen, the height of the mst n the pex hlf-ngle, ll of whih in turn etermine the height of the en insultors ove the groun. In the uthor s se, with the frequenies hosen, mst height of 8m n n pex hlf-ngle of 68º, the en insultors of the 20/40/80m inverte-v re out 60m (2ft) ove groun. Douling the height of the en insultors ove groun to 120m (4ft) inreses the resonnt frequeny to 3.830MHz (n inrese of out 1.8%), whilst lowering them y 60m (2ft) to groun level lowers the resonnt frequeny to 3.690MHz (this time erese of out 1.8%). It is pprent tht the 80m ntenn n e fine-tune y inresing or eresing the height ove groun of the en insultors (hieve y longer or shorter ors). The uthor feels this is nother spet of inverte-v ntenns (with en insultors lose to the groun) whih is rrely, if ever, me ler. (Note: In eh se, we re hnging the pitne of the ntenn groun. Bringing the ens loser to groun inreses the pitne, thus eresing the resonnt frequeny, n vie vers). There is negligile effet on 20m n 40m. (3) Nture of the groun The figures erive in this rtile refer to verge groun, if there is suh thing. Experiene suggests one shoul, where possile, voi soli rok, sn or severe unultions in the line of the ntenn. Sometimes, however, hoie is not n option, n vritions in proximity to groun n in its onutivity, my ffet the resonnt frequenies n input impenes, n hve, on osion (rrely, fortuntely), use some serious he-srthing! (4) Dimensions Tle 1 gives the lengths of eh leg of 20/40/80m inverte-v ipole. These lengths re the istnes etween the fixe en-points (in effet, the wing-nuts, or in the se of the lower en of the 80m segment, the entre of the en insultor). The 20m- n 40m-n frequenies re se on the verge of the IOTA CW n SSB frequenies for the 20m n 15m ns, respetively. As previously stte, the 15m n is ville on the 20/40/80m version y using the 40m ipole s 3λ/2 ipole for 15m. Similrly, the 20m ipole hs een use (40/80m isonnete) s 3λ/2 ipole on 86 April 2005 RCom

5 10m, y ing out 2.4m eh sie n llowing these itionl lengths to hng freely from the 20/40m insultors. Tle 2 gives the lengths of eh setion in eh leg of the 10/12**/15/17/30m version of the multi-n inverte-v. CONCLUSIONS This form of inverte-v llows multin opertion with one ntenn from portle lotions. It might e rgue tht it is perhps not quite so onvenient for the home lotion. This si, how often is rpi n frequent n hnging require, even t home? The uthor (together with Isln prtners Alex, GM0DHZ, n Keith, MM0BPP,) hs me over 100,000 QSOs from gret vriety of isln lotions. With the inverte-v esrie, he hs never neee to use n ATU, other thn in exeptionl irumstnes suh s n ntenn system fult (roken onutor, or orrosion, or in n extremely verse lotion. A site ner the wter (ielly over the wter) n lose to the lning point is lwys hosen in preferene to height ove se level. Aprt from nything else, the ltter reues the istne the equipment hs to e rrie. The formule n imensions propose re the result of muh experimenting n experiene. They pper vli whether the ntenn is ner the se or fr remove from it, n represent goo strting point for nyone ontemplting putting up n inverte-v. There is no out tht suh n ntenn will out-perform horizontl ipole whose entre my e sgging well elow the height of the en supports, n unfortuntely ll-too-fmilir sight. If using 0 to 17m inverte-v, ensure tht the pex ngle is not less thn 110º (with the 20/40/80m version top n 8m mst, the pex ngle will generlly e greter thn 130º). In limite spe, one n swing the ens roun slightly. FINALLY In his pst life s 5Z4KL in the 60s n 70s, the uthor frequently n suessfully use the uiquitous G5RV, in its fmilir form using 300Ω rion le n 75Ω ox, lwys in inverte-v onfigurtion, n often in the ush t heights s low s 6ft ove the groun. Vlve rigs were very forgiving not so toy s soli-stte 50Ω output rigs n mplifiers. Prior to using G5RV ipole s multi-n ntenn, you woul e well vise to re the work one y ZS6BKW (see Prtil Wire Antenns, y John Heys, G3BDQ) on improving this RCom April 2005 Tle 1: Lengths of eh leg of n inverte-v ipole. Bn Chosen esign Blun swith Feeline (13.6m λ/4 extr length in (m) frequeny (MHz) position of 50Ω ox) (68/f, m) eh se (m) :1 2λ/ (15ft 9in)* :1 λ/ (31ft 8in)* 4.84 (15ft 11in) :1 λ/4 txfmr (59ft 1in)* 8.38 (27ft 5in) * These re lengths on either sie of the fee-point the overll length is oule this. Tle 2: Lengths of eh setion in eh leg of the 10/12**/15/17/30m version of the multi-n inverte-v. Bn Chosen esign Blun swith Feeline (13.6m λ/4 extr length in (m) frequeny (MHz) position of 50Ω ox) (68/f, m) eh se (m) :1 4λ/ (7ft 11in) 12** [24.940] 1:1 ~7λ/4 [2.73] (8ft 11in) [0.32] (1ft 0in)** :1 3λ/ (10ft 7in) 0.81 (2ft 8in) :1 ~5λ/ (12ft 4in) 0.53 (1ft 7in) :1 ~ 3λ/ (22ft 0in) 2.97 (9ft 8in) ** In prtie, the extr length (with its own U spe terminl) for the 12m n (reltive to 10m) is tpe to the sie of the 15m setion n the pproprite spe terminl is onnete to the en of the 10m setion epening on whether 12m or 15m is selete. Tle 3: Dimensions for the 20/40/80m version epite in Fig 6. Bn Chosen esign Blun swith Feeline (13.6m λ/4 extr length in (m) frequeny (MHz) position of 50Ω ox) (68/f, m) eh se (m) :1 λ/2 9.65m (31ft 8in) :1 2λ/ m (49ft 2in)# 5.33m (17ft 6in) :1 λ/4 txfmr 17.91m (58ft 9in)## 2.93m (9ft 7in) # NB: The length of the 3λ/2 ipole is greter thn 204/f ( 3 x 68/f). This is euse the shortening ue to en-effet ffets only the outer 1/2-wvelengths of the 3λ/2 ipole. The ARRL Antenn Hnook suggests tht the length of horizontl 3λ/2 ipole is out 442/f metres rther thn 426/f (3 x 142/f ). In the sene of ny urte, theoretilly-se formul, the uthor pplie simple proportion n preite n empiril vlue of 212/f. This gve length of 14.98m for eh leg of the 3λ/2 inverte-v ipole, whih is inee lmost extly the vlue of the length he otine y experiment! The uthor woul therefore suggest the use of Eqution 5. ## The itionl length for 80m resonne is out 4in less thn preite y the 1/2-wve formul (68/f) previously propose. This is negligile on 80m. In ny se, the ens of the 80m ipole re fole k on themselves pproximtely 40-50m (18in) to llow preise justment of the 80m resonnt frequeny in situ. The uthor psses the wire through one hlf of twin terminl lok onnetor (preferly with rss srews), then through the egg (or other insultor) n k into the onnetor lok. This llows esy justment, without utting the surplus wire. FIG 6 RADCOM 450 Blun 8x1m mst ntenn, n the resons for oing so. This ook lso gives guine on the esign of oulet rguly fr etter multi-n lterntive for the soli-stte home sttion using G5RV s own imensions, hosen to voi unwiely retnes. λ 40m ( 2 ) I 1 n I 2 : insultors 20m ( 3λ 2 ) I 1 APPENDIX new onfigurtion Sine rfting this rtile, the uthor hs teste nother onfigurtion for the 20/40/80m version of his multi-n inverte-v ipole. It ourre to him tht, y mking the innermost ipole the 40m one, the next segment oul e use to exten this to 3λ/2 (three hlfwvelengths) on 20m. The length of the thir segment on eh sie is juste oringly to llow resonne s efore on the 80m n. Dimensions re given in Tle 3. λ 80m ( 2 ) I 2 just Fig 6: Alterntive onfigurtion for the 20/40/80m ntenn, whih is 3λ/2 on 20m. 87