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home | newest check | boards | help index | log | ps | userlogin | send sysop | slog | status forward | bcm news | users | version | remove cookieG8MNY > TECH 26.04.24 16:34l 118 Lines 5244 Bytes #7 (0) @ WW BID : 6319_GB7CIP Subj: Diamond X500 Colinear Repair Path: JH4XSY<JE7YGF<LU4ECL<ED1ZAC<GB7CIP Sent: 240426/0723Z @:GB7CIP.#32.GBR.EURO #:6319 [Caterham Surrey GBR] $:6319_GB From: G8MNY@GB7CIP.#32.GBR.EURO To : TECH@WW By G8MNY (Update Sep 22) (8 Bit ASCII graphics use code page 437 or 850, Terminal Font) This old 5.2m (17ft) tall high gain 200W dual band colinear aerial has 8.3dB gain on 2m & 11.7dB gain on 70cms. But my one ended up being internally water- logged, with the water ending up dripping out of the shack coax, after passing through the N connector. (the only way out!) Lots of preparation was needed to take it down as it was at 30ft up, on a 12ft pole lashed to a chimney. Then dismantle it (not loosing which part is which) and test each component for failure, clean up, repair all the parts etc. The aerial consists of 3 complex sections:- ウ ________ウ MOUNTINGロ''''''''''''''''''''ロロトトトトトトトトトトトトトトトトトトトトトトトワワ.................... TUBE ロ BOTTOM ロロ_______________________ロロ....................ロ トトトトトトトト゚'''''''''''''''''''' MIDDLE TOP ウ3 ウRadials BOTTOM SECTION This has two aluminium tubes, outer one has the two mast support clamps. The inner tube is held in position with bolt (unless corroded solid as my one was!) Inside is a machined up brass N socket connector disk, that screws into the inner tube. (corroded solid). The disk supports a PTFE insulation stalk 10mm dia where the 4.5 turn matching coil is wound. It is tapped 2 turns up by a 10pF C from the N socket, and the top of coil has a tuning C of 1.5pF to ground & the aerial rod brass ferrule joiner. The coil tuning capacitance is also to the inner tube! The inner tube has the bottom fibreglass pole bonded inside it. Radials Bolt -------=================== Fibreglass tube painted white _ウウCoil> _~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~_ N[_ _////_[_]-----------------\\\\---------[]\\\\\\\\\\\[]-------[_] con ウウ 2 caps _____________________________________________________ -------=================== Outer Support Tube with 2 mast clamps The internal 1/8" brass rod aerials has a 70cms 8 turn hard copper phase coil and longer 2m 61 turn coil on a fibre rod, spaced along the aerial. The rod joiners are either a stainless clip, or brass ferrule and screw, or a hex grub screw. Sponge (sticky draft excluder) is wrapped around any part that could touch the fibre glass tube as a vibration spacer. MIDDLE SECTION This is a thinner tube and has lower ferrule and seal for inter tube joining. Inside is 2 x 6 turn coils separated by a mechanical capacitor boss and the rods to a 61 turn coil. __.----. Fibreglass tube painted white ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~_ -----------\\\\------[c]------\\\\---------------[]\\\\\\\\\\\[]-----[_] ___________________________________________________________________ ~~'----' Ferrule joint and water seal TOP SECTION This tube is thinner still, and has a metal top cap. It has a ferrule and seal for inter tube joint. Inside there is a joiner feeding a rod & 2x 6 turn coils separate by a mechanical capacitor boss, and the long top rod. __.----. Fibreglass tube painted white __ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ウmetal -----------[ア]------\\\\------[c]------\\\\----------------------- ウtop ___________________________________________________________________ウcap ~~'----' ~~ Ferrule joint and water seal THE REPAIR After undoing the ferrules, the water came out, and inner wire jointing screw undone to free up the upper 2 sections. I had to cut a long slot down the outer support tube with an angle grinder, to free it from the inner tube. And that slot not only freed it, but let me see the corroded in inner brass disk thread, which I was then able to leaver it out and undo the hex grub screw in the ferrule, freeing the bottom loading unit from the rods. On RF testing it, I found the bottom coil resonated, but above 2m and 70cm until I put back the inner tube again. Result the wet coil and 2 caps were still all OK! I polished up all the copper aerial coils, brass rods, joiners and line caps with a wire wheel. Then greased up all joint bosses, aluminium soldered up any loose crimp joints. And I replaced the sponge vibration spacers (turns of sticky draft excluder stip). The fibreglass tubes were not cracked, but needed a spot of paint, the faulty water seal rubber ring was replaced in the bottom ferrule. To stop any further water problems, I carefully drilled a 2mm drain hole in the brass disk near the N connector avoiding the 2 small 1kV caps. REASSEMBLY Initially done for RF testing to see if it all still worked. SWR 1:12 in the middle of 2m & OK on 70cms with aerial horizontal 1.5m above ground on wooden supports. The tests repeated again after spraying anti corrosion metal protection on the aerial components, and then again over the final assembly. On re-errecting on taller 16ft pole with new lower loss coax, the aerial was now @ 35ft in the clear it worked very well, compaired to a backup 9ft triband colinear in the loft. Why don't U send an interesting bul? 73 de John G8MNY @ GB7CIP
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