I would hate to give up the efficiency of an over-resonated T, even if field strength isn’t significantly better than an L design. I think two design issues help to avoid pattern distortion to nearby HF Yagis.
First, as Frank suggested, keep the length of the horizontal T wire non-resonant on any given band, including non-harmonically related bands like 30m. It's not necessary to select a T top wire length that results in resonance at the base feed, at least with a single omni antenna. Secondly, there's a difference in interaction between a T that's installed broadside to a Yagi versus one that's installed perpendicular off the end of a Yagi. For example, If a T is installed between two towers that are spaced 150 ft apart and a 40m Yagi is atop one of the towers, the T top wire is never broadside to the Yagi. It's looking straight down a piece of wire. It's no different than a Yagi director that's rotated 90 degrees to the driven and reflector elements. In fact, an existing Yagi design file could be modeled that way only with a rotational change to the director's Cartesian coordinates and a change in distance from the DE. No doubt modeling will still show some interaction but what remains should be cured with an optimum, non-resonant director length. Paul, W9AC -----Original Message----- From: Topband <[email protected]> On Behalf Of Guy Olinger K2AV Sent: Friday, February 28, 2020 12:16 PM To: W7RH <[email protected]> Cc: [email protected] Subject: Re: Topband: T Top Verticals and yagis That’s an awful lot of effort just to keep a T top. There are a number of effective alternatives to the traditional T top without the interaction drawbacks. Inverted L is only the dirt simple one without the skip-zone-making high angle hole in the pattern. 73, Guy K2AV On Fri, Feb 28, 2020 at 9:46 AM W7RH <[email protected]> wrote: > The discussion has involved horizontally polarized Yagis. Perhaps use > a vertical 8 circle array on 40m! LOL And keep your T-Top! > > Bob, W7RH > > -- > W7RH DM35qj > > "It has become appallingly obvious that our technology has exceeded > our humanity." - Albert Einstein > > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > -- Sent via Gmail Mobile on my iPhone _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
