Topband
[Top] [All Lists]

Re: Topband: T Top Verticals and yagis

To: <topband@contesting.com>
Subject: Re: Topband: T Top Verticals and yagis
From: "Paul Christensen" <w9ac@arrl.net>
Date: Fri, 28 Feb 2020 15:36:56 -0500
List-post: <mailto:topband@contesting.com>
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 <topband-bounces+w9ac=arrl.net@contesting.com> On Behalf Of 
donovanf@starpower.net
Sent: Friday, February 28, 2020 3:00 PM
To: topband@contesting.com
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" <w9ac@arrl.net>
To: topband@contesting.com
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 <topband-bounces+w9ac=arrl.net@contesting.com> On Behalf Of Guy 
Olinger K2AV
Sent: Friday, February 28, 2020 12:16 PM
To: W7RH <midnight18@cox.net>
Cc: topband@contesting.com
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 <midnight18@cox.net> 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
<Prev in Thread] Current Thread [Next in Thread>