Timeline for Multi-wire EFHW?
Current License: CC BY-SA 4.0
20 events
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| Mar 20, 2022 at 23:02 | comment | added | EdvinW | I don't know why it works, but I can testify that it does. I use this method to tune the SWR of endfed antennas when I'm portable, and sometimes adding half a meter (or even less) of wire hanging from the feedpoint of an efhw can knock the SWR of an efhw down from >2 to <1.5. I don't have any precise system, but try various configurations until it works. | |
| Sep 21, 2020 at 19:45 | comment | added | Brian K1LI | @JayHDee Now that I know the total length of wire and coax, I believe your analysis may be correct. Can't really comment on raising the coax, but it seems like a good idea. If it's not too difficult, give it a try! | |
| Sep 21, 2020 at 18:30 | comment | added | JayH Dee | @brian-k1li OK, so this is essentially an OCFD, with the center conductor leg being the ~50ft wire and ~6ft wire (I removed one of the 2 shorter wires which got me better SWR on 80m/20m/10m but sacrificed 40), and the ground conductor leg being the feedline (50ft RG8X) & 4ft counterpoise. That makes a bit more sense, and I'd forgotten about the radiating effect of the coax shield. This has been quite an effective ant. on 80m-I've managed make contacts into Europe with it up about 28ft. Would it improve things if I elevated the coax, because that 50ft of coax is just sitting on the ground? | |
| Sep 21, 2020 at 12:30 | comment | added | Brian K1LI | @JayHDee Like a half-wave dipole, the radiating portion of an OCFD should be isolated from the outside of the coax shield by a choke, to prevent the feedline from becoming part of the radiating and resonating system. Page 4 of your citation says, "Additional counterpoise is not normally required, as the coax shield provides the counterpoise function." This means that the outside of the coax is intended to be part of the resonant system; it will carry current, radiate and present RF potential. Since the length of this conductor is not specified, it's impossible to know its influence. | |
| Sep 21, 2020 at 2:05 | comment | added | JayH Dee | @brian-k1li There is an error in my post: The EARCHI Matchbox antenna is a 9:1 unun. earchi.org/92011endfedfiles/Endfed6_40.pdf. Maybe that changes things a bit? Not sure how I'd go about measuring the impedance of the feedpoint of the wires. Also, I havent exactly measured any of the wire lengths (they're now up on poles) but the long wire is about 45-50ft. I agree that it seems like an offcenter fed dipole, but isn't one of the ends of an OCFD attached to the ground/coax shield? All of these wires are purely attached to the center conductor, except for the counterpoise. | |
| Sep 19, 2020 at 15:27 | comment | added | Brian K1LI | I can't come up with a NEC2 model that produces anything like the impedance measurements you obtained. The configuration of wire is reminiscent of an off-center-fed dipole with multiple wires on the longer side of center. It would be very useful to know the impedance at the feedpoint of the wires, as opposed to the feedpoint of the matching unit. | |
| Sep 19, 2020 at 11:26 | answer | added | Phil Frost - W8II | timeline score: 3 | |
| Sep 19, 2020 at 1:55 | history | edited | JayH Dee | CC BY-SA 4.0 |
Added VNA plots and descriptions
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| Sep 19, 2020 at 0:40 | history | edited | Mike Waters |
edited tags
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| Sep 18, 2020 at 23:42 | history | edited | JayH Dee | CC BY-SA 4.0 |
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| Sep 18, 2020 at 23:36 | history | edited | JayH Dee | CC BY-SA 4.0 |
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| Sep 17, 2020 at 21:23 | comment | added | JayH Dee | Brian. "Sorta". The ~60ft wire is a sloper at 30ft running down to the top of the fence. The other 2 wires (actually I think they are about 6-9ft each, not exact and not identical) are strung from the matchbox along the fence for one, and to another wooden stairway for the other, both at 5ft above ground. The counterpoise is about 3 feet long and basically does just hang down. I do have a NanoVNA and will post some plots. The counterpoise makes some difference, but not a lot. I have a T240-43 toroid with about 8 loops of coax wrapped around it as a choke, close to the radio. | |
| Sep 17, 2020 at 15:31 | answer | added | webmarc | timeline score: 1 | |
| Sep 17, 2020 at 14:37 | comment | added | Brian K1LI | Thanks for your interesting question! Does the drawing accurately describe the antenna's physical configuration? How long is the "counterpoise?" Do you have a common-mode choke on the coax to the transmitter? | |
| Sep 17, 2020 at 8:48 | comment | added | Marcus Müller | Thanks! I've created a minimal tag description | |
| Sep 17, 2020 at 8:33 | comment | added | JayH Dee | End Fed Half Wave | |
| Sep 17, 2020 at 8:24 | history | edited | Marcus Müller | CC BY-SA 4.0 |
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| Sep 17, 2020 at 8:21 | review | First posts | |||
| Sep 17, 2020 at 15:05 | |||||
| Sep 17, 2020 at 8:17 | comment | added | Marcus Müller | Hi! Welcome here! Out of interest: what's an EFHW? | |
| Sep 17, 2020 at 8:14 | history | asked | JayH Dee | CC BY-SA 4.0 |