I believe you must get into several wavelengths before you get significant end directivity from a "long wire". My reference says that the angle of the main lobe to the antenna is about 55 degrees when the wire is a wavelength long, compared to 90 degrees at 1/2 wavelength. It takes a wire more than 7 wavelengths long for the angle of the main lobe to 20 degrees off of the end.
For a horizontal wire, the angle of maximum radiation with respect to the horizon continues to be a function of height in wavelengths above ground. So, for a given wire a specific height above ground, as the frequency goes up, the lobes will slowly move toward the end and should be at an even *lower* elevations in the higher frequencies since the wire is higher above ground in terms of wavelengths. Of course one has to feed the wire. That's why most of us who use an end fed wire have it arranged as an inverted "L". Mine is about 40 feet vertical from the rig, then 90 feet horizontally. So the radiation is a strong mix of vertical and horizontal polarization. On my favorite band, 20 meters, the vertical section is about optimum for low-angle vertical radiation and the height is perfect for low angle horizontal radiation. It works very well across the HF spectrum. I use an external homebrew tuner to provide physical separation between the very RF hot (on some bands) end of the wire and the rig (and me at the rig). As for impedance, it will be highest and 1/2 wavelength and diminish at longer lengths. Cranking a sample antenna into EZNEC shows that the impedance of a typical real-world wire at 1/4 wavelength long is about 35 ohms as expected. At 1/2 wave it's about 1500 ohms. At 1 wavelength it's about 800 ohms. At 2 wavelength it's about 300 ohms, and so on. Of course many things affect the actual impedance including the diameter of the radiator itself. Ron AC7AC -----Original Message----- I'm not sure I see the advantage. A full wave end fed antenna would theoretically have the same very high feedpoint impedance, and would additionally blow most of it's radiated energy at a fairly high angle off the ends of the antenna instead of broadside at a lower angle. If you find it that easy to tune, I suspect that electrically it really isn't that close to a full wavelength ... possibly because of coupling to earth (if it is low) or nearby structures. Either that or there is a lot of loss in the system somewhere. 73, Dave AB7E On 8/24/2011 2:14 PM, Niel Wiegand wrote: > Phil, > > You might try a 67' length of wire (EFFW antenna). I've used that (and a > 32' EFHW) on 20 a lot with my K1 with the KAT1 installed...tunes to > close to 1:1 just fine. > > Have fun at Crater Lake. There are some neat places along the rim for > hamming. It's a 2000 mile drive (one way) for me but I've gotten there > twice within the past several years. See > http://www.prismnet.com/~nielw/qrp/CraterLake_july04.jpg and > http://w0vlz.blogspot.com/2009/08/after-three-weeks-5300-miles-and-12.html > > 73, > Niel - W0VLZ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
