If a 40m yagi points towards an 80m or 160m dipole in its neighbourhood the yagi pattern will be ruined as well.
73 Peter -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of [email protected] Sent: Freitag, 28. Februar 2020 23:08 To: [email protected] Subject: Re: Topband: T Top Verticals and yagis Hi Paul, A little modelling will answer the question more completely and accurately than I can answer it in writing. I was referring to the case where a 40 meter Yagi is on one tower and a T-vertical with a top length of 60-75 feet is suspended between the tower and a fairly nearby second tower. Lets say -- for the purpose of discussion -- that the two towers are in a north-south line. If you point the 40M Yagi East or West (perhaps +/- 45 degrees), the top of the T-vertical will be either below the Yagi or off to its side. If its less than 70 feet below the Yagi, the T-top will significantly degrade the performance of the 40M Yagi. Its is off to the side of the Yagi with a separation of at least 35 feet or so, degradation of the Yagi will be minimal. Detailed evaluation is best done by modelling, its very easy to do. 73 Frank W3LPL ----- Original Message ----- From: "Paul Christensen" <[email protected]> To: [email protected] Sent: Friday, February 28, 2020 8:36:56 PM Subject: Re: Topband: T Top Verticals and yagis Frank, Perhaps you can clarify what you mean by "parallel." Are you referring to the T top in parallel and *in front* of the 40m Yagi? Or, do you mean in parallel with the Yagi but off to the side by 90 degrees as in the case of a T strung between two towers, with the 40m Yagi atop one of the towers? In both cases, the T is in parallel with the Yagi. A picture would speak a thousand words here, but asking the question in words is the best I can do! Paul, W9AC -----Original Message----- From: Topband <[email protected]> On Behalf Of [email protected] Sent: Friday, February 28, 2020 3:00 PM To: [email protected] Subject: Re: Topband: T Top Verticals and yagis Hi Paul, If you model -- or build -- a 40 meter Yagi with a nearby T-top vertical with a 60-75 foot top, you'll discover that when the 40 meter Yagi is turned so that its elements are parallel -- or near parallel -- to a nearby T-top the impact on the performance of the 40 meter Yagi is severe. Been there. Done that... 73 Frank W3LPL ----- Original Message ----- From: "Paul Christensen" <[email protected]> To: [email protected] Sent: Friday, February 28, 2020 12:45:19 PM Subject: Re: Topband: T Top Verticals and yagis 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 _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
