After reading Jeff's comments I decided to look into my resource of antenna publications to confirm or refute the information he presented and was unable to find anything contrary to his words (with a minor exception to the feeding of a "J" antenna). My sources were: Radio Engineers Handbook by Terman Antenna Engineering Handbook by Johnson & Jasik Antennas by John Kraus Transmission Lines, Antennas, and Waveguides by King - Mimno - Wing Directional Antennas by G. H. Brown Microwave and Radar Antennas by Richard F.H. Yang Antennas and Radio Propagation Dept.of the Army TM 11-666 Principals of Radar, 3rd Ed. by J. Francis Reintjes and Godfrey T. Coate Reference Data for Radio Engineers, 5th Ed. H.P. Westman, Editor VHF - UHF Manual by D.S. Evans & G.R. Jessop A very good presentation Jeff. I found no information what-so-ever to backup the "5% rule". Allan Crites WA9ZZU
--- On Sun, 2/21/10, skipp025 <[email protected]> wrote: From: skipp025 <[email protected]> Subject: [Repeater-Builder] Re: Ground Plane 5% longer radiator ... To: [email protected] Date: Sunday, February 21, 2010, 6:14 PM Hello Sailors, Well, I'm offended this $%#*& laptop wants to send my posts premature when I hit the wrong key... but that's not related to the topic. I'm going to make some statements I don't care (at this time to back up with hard proof. If you model a ground plane feed point resistance it will not be a perfect 50 ohms. You can do a number of different things to a ground plane to change or modify/move the base/feed point impedance to a more favorable or desired value. One options is to angle the radiators at a 45 degree angle (downward). I'm not fonda' Jane (as are most Vets), nor am I fond of non DC Grounded Antennas, which would be the case with a more standard single vertical radiator Ground Plane Antenna. I like the DB-201 antenna but I think the hair pin is a bit over kill in the amount of hardware (metal) hanging out there in the wind even though the DB-201 is a fairly robust antenna design. In the middle of all my years of playing with antennas I found and stole the beta match method of matching a ground plan. I shorten the vertical radiator and then match it with a simple, small hair-pin inductor at the base. Or depending on how you look at it I leave the horizontal ground plane elements about 5% longer than the vertical element. What the above layout does is provide not only a much better (closer) 50 ohm base point impedance... but also a true strong DC Ground (return) Connection. I still have a copy of the 1970's era antenna paperwork where I first saw and lifted (stole) the information from... and it wasn't the ARRL. In addition to all this cannon fodder I should mention the horizontal radiators remain perpendicular to the mast so you don't have to mfgr some type of a special bent angle mounting bracket for the rods, which would otherwise be best optimized at 45 degrees. Modeling a Dipole feed impedance is easy when compared to all the possible Ground Plane configurations. cheers, skipp > "Jeff DePolo" <j...@...> wrote: > At the risk of offending someone somewhere, the fact that > the ARRL cites the "5% rule" without backing it up with the > analysis behind the rule doesn't really suprise me... > > Think about it this way. If you made a dipole, would you cut > one side 5% longer than the other? > > Why not make the vertical radiator 5% longer, and leave the > radials exactly a quarter-wave, thereby saving on materials? > > You know I'm not taking a dig at you Chuck - I'm just waiting > (hoping) that someone comes up with some real evidence to back > up the 5% rule. > --- Jeff > > > Various ARRL publications cite the 5% longer "rule." Right or > > wrong, who > > knows? > > > > Chuck > > WB2EDV >
