I've gotten to the point, that before I say anything about a model, I actually run it and play with it, to make sure I haven't forgotten something, or remembered something wrong.
As to that particular antenna a center fed half wave antenna is troublesome. The better version of that if one wants that pattern is the extended double zepp, two 5/8 waves fed in phase, where you are feeding a lower impedance at the center, and it's a far less cranky antenna. The double zepp maintains its essential shape fed at 45% whereas the halfwave converts to cloverleaf. That's ancient knowledge, garnered by experience in the 40's and 50's without the benefit of software. These days if you can't look it up for free on the internet, it's forgotten. 73, Guy. On Fri, Aug 26, 2011 at 12:17 PM, David Gilbert <xda...@cis-broadband.com>wrote: > > Yup ... I was wrong again, but the trouble is I can't figure out why. I > mean, it's easy to verify the cloverleaf pattern with EZNEC and I have done > so, but I know that I have modeled something similar with an off-center feed > in the past and gotten an end-fire pattern. As soon as I figure out what > that was I'll come back here and try to clear up the confusion I have > caused, but in the meantime let's all just agree that I don't know what I'm > talking about. > > sigh ... > > 73, > Dave AB7E > > > > > > On 8/25/2011 11:13 AM, Guy Olinger K2AV wrote: > > Sorry to interject, but a fullwave fed at the 25% point has a clover leaf > pattern. It only has the two halfwaves in phase colinear behavior when fed > very near the center. Even fed at 45% it has a significant cloverleaf lobe > and a NULL in the center Easy to verify with any modeling program. 73, > Guy. > > On Wed, Aug 24, 2011 at 8:37 PM, David Gilbert > <xda...@cis-broadband.com>wrote: > >> >> Yes, Don ... you are totally correct. For some reason I was thinking >> about a full wave antenna fed at the 25% point (I have built such >> antennas before), which looks like two colinear half waves fed out of >> phase. The current phasing along the antenna would indeed be much >> different and give a cloverleaf pattern if it were end fed. I >> wholeheartedly apologize for any confusion I may have created. >> >> 73 and thanks for catching my mistake. >> >> Dave AB7E >> >> >> On 8/24/2011 3:23 PM, Don Wilhelm wrote: >> > Actually Dave, a full wavelength wire will have a " 4 leaf clover" >> > pattern - that is neither broadside to the antenna, nor off the ends. >> > Check out the pattern for a 1 wavelength long wire in the ARRL Antenna >> > Book. The maximum radiation is about 28 degrees from the wire - the >> > radiation from the end is almost zero. >> > >> > The elevation angle of maximum radiation is similar to a half wave >> > dipole - about 15 degrees with a lesser lobe at 45 degrees (that is >> > for a wire 70 feet high, at lower heights, the angle will be greater). >> > >> > 73, >> > Don W3FPR >> > >> > On 8/24/2011 5:34 PM, David Gilbert wrote: >> >> >> >> 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 >> >> >> > >> ______________________________________________________________ >> 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 >> > > ______________________________________________________________ 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
