Just about the only wire antenna in common use I had not experimented with is the End Fed Half Wave(EFHW).\u00c2\u00a0 So WTF.\u00c2\u00a0 May as well give it a go.\u00c2\u00a0<\/p>\n
2021 planning had me booking a stay on Cape Lookout National Seashore(CALO) for the end of June rather than the end of July.\u00c2\u00a0 I tried unsuccessfully to make the reservation in 2020, but could not.\u00c2\u00a0 Success for 2021.\u00c2\u00a0 So my FD 2021 will be from Cape Lookout.\u00c2\u00a0<\/p>\n
Given the layout of the cabin I prefer at CALO campground I decided to tinker with the EFHW as a possible solution for allowing multi bands with least effort.\u00c2\u00a0 The “least effort” factor is growing more important with each passing year.\u00c2\u00a0 But the EFHW itself piqued my curiosity as well, and it seems it my provide a solution to the “least effort” vs. “works well”\u00c2\u00a0 conundrum.\u00c2\u00a0\u00c2\u00a0\u00c2\u00a0<\/p>\n
So, here lies the experimental portion. \u00c2\u00a0 NUMEROUS versions of the classic 49:1 transformer are documented on WWW and in the now ubiquitous scrootoobe video.\u00c2\u00a0 Version guidelines exist for either 80m or 40m multi band versions.\u00c2\u00a0 Quite typically I chucked some of that and decided to re-invent the wheel – because what is the fun of experimenting if you are just going to follow the cookbook?\u00c2\u00a0 Wellll…..not quite that either.<\/p>\n
Looking for a 40m size and decided to try modeling out a 40m EFHW fit out with a loading coil and tag end to allow 80m or 75m.\u00c2\u00a0 The idea is to have an antenna that the floppy fiberglass masts would be able to support easily in the normal 20 knot winds typical on CALO.\u00c2\u00a0 The feed point will be at about 4 feet high as I expect to deploy it.\u00c2\u00a0 The mast will support the wire vertically to about 30 or 35 feet, depending on which mast is used(Spiderpole or Jackite or K4TMC)<\/a>.\u00c2\u00a0 The rest of the wire will be stretched out horizontally with the coil supported by a second mast.<\/p>\n This deployment will have 80m or 40m basically functioning as half wave in an L configuration.\u00c2\u00a0 20m will probably have a larger horizontal component than the vertical section, and if it works there 15m\/10m will provide who-knows-what.\u00c2\u00a0 i.e., “PERFECT!” – for values of “perfect” where whatever happens is perfect.<\/p>\n Modeling showed best result with the wire between the feed and the load at a longer length than I expected at 70+ feet.\u00c2\u00a0\u00c2\u00a0 Using insulated wire for actual construction, I expect that to be shorter in real life.\u00c2\u00a0\u00c2\u00a0 I plan to test with a .05wave counterpoise, and use a 6 foot coax jumper at feedpoint.\u00c2\u00a0 The real feedpoint will be a current choke at the end of the coax jumper.\u00c2\u00a0 It seems likely the shield of the coax jumper will act as another counterpoise.\u00c2\u00a0 Maybe another choke at the radio end.<\/p>\n The item I had more questions about was the step-up transformer.\u00c2\u00a0 A lot of conventional wizzdom surrounding the 7:1 turns ratio versions.\u00c2\u00a0 I chose to give myself more options and provide multiple taps, and use the larger ft-240-43 size toroid to allow 100w. \u00c2\u00a0 Hopefully this will give less core heating.\u00c2\u00a0 Then two turns vs. three turns on the primary was considered.\u00c2\u00a0 Initially I favored using three turns on the primary. \u00c2\u00a0 I expect 80m to be more useful than 10m going forward.\u00c2\u00a0\u00c2\u00a0 Physical reality – two turns seemed more practical with the 16ga wire I used.\u00c2\u00a0<\/p>\n The other wildcard I threw into the construction detail was about sticking to the “norms” of putting the taps on nice-and-easy turns ratios.\u00c2\u00a0\u00c2\u00a0\u00c2\u00a0\u00c2\u00a0 While waiting on my toroid order to arrive, I stumbled across N8NK’s videos.\u00c2\u00a0 I found the playlist on EFHW and UNUN’s interesting viewing.<\/a>\u00c2\u00a0 The main idea I fortified was to tap the toroid in several different places.\u00c2\u00a0 That would have been more versatile using 3:1 windings.\u00c2\u00a0 Even with 2:1 windings I still liked the range of impedances available by placing “irregular” taps, i.e not on the even multiple windings.\u00c2\u00a0 With 3:1 I had expected to place the taps on every 4th turn.\u00c2\u00a0 With 2:1 windings I thought maybe every 3rd turn but with 6 taps every 2nd turn was “good enough”.<\/p>\n The only genuine benefit that conventional “even numbered taps” provides is ease in predicting\u00c2\u00a0 the transformation factor(i.e., 7:1 turns gives 49:1 step up).\u00c2\u00a0 To switch the flip I decided to tap the transformer at 4.5:1, 5.5:1, 6.5:1, 7.5:1, 8.5:1 and 10:1.\u00c2\u00a0 (FWIW, that should be stepping 50 ohms up to about: 1013, 1513, 2113, 2813, 3613 or 5000 ohms.)\u00c2\u00a0 Just for grins, it is easy to test with the ordinary antenna analyzers and a resistor test box(or well stocked junk box).\u00c2\u00a0\u00c2\u00a0<\/p>\n If it is important to your thought process, measure the damn unun to be sure.\u00c2\u00a0 To simplify, the secondary is actually tapped on turn #9,#11,#13,#15,#17, and #20.\u00c2\u00a0 With 2 primary turns and just 5 taps on secondary, tapping every 3 turns at #8, #11, #14, #17 and #20 should allow matching impedances of 750, 1513, 2450, 3616, or 5000 ohms.\u00c2\u00a0 That includes the obligatory 7:1 ratio for purists.\u00c2\u00a0 I only chose to use the odd taps as an appeasement to my increasingly contrarian curmudgeonly nature.<\/p>\n \u00c2\u00a0I figure to just use the antenna with the tap that provides the best SWR. I can then produce a cheat sheet for each band.\u00c2\u00a0 I would like to have a best choice for each band.\u00c2\u00a0 If it turns out the same tap works best for all bands – so much the better.\u00c2\u00a0\u00c2\u00a0 If they are NOT all the same tap I also want compromise choices that will allow one tap to allow operation on several bands without moving the tap.\u00c2\u00a0 Another tradeoff option – sometimes moving the tap will be easy, sometimes inconvenient.<\/p>\n Functionally we can call it good if some doing RBN compares to permanent dipoles prove it to perform acceptably.\u00c2\u00a0 The truth is I don’t care what the actual step up ratio might be.\u00c2\u00a0 I just want the antenna to function, and experimentally finding a good tap is “good enough”.\u00c2\u00a0 We are hoping that the taps provide enough options for multi-band operation with a good match.\u00c2\u00a0 It will be nice if a single tap is good on all bands.\u00c2\u00a0 It is not a deal breaker if changing bands requires moving a tap that can be reached at ground level.<\/p>\n Engineer the possible. Mind the trade-offs, because “best” can be the enemy of “good enough”.<\/p>\n End Fed Half Wave Experiment – Part 2<\/a> nonstopsystems.com Multi-Band End Fed Antenna<\/a><\/p>\nTransformer Conundrums<\/h5>\n
Precision Optional<\/h5>\n
Related Links(updated 2021\/03)<\/h5>\n
End Fed Half Wave Experiment – Part 3<\/a><\/p>\n