[TowerTalk] T-match?

[i4jmy@iol.it]

Like it or not, the boom lenght, sooner or later becomes the basical 
and physiological limit to any project.
Fixed the boom, best results are theorically obtained "compressing" the 
cell that includes Reflector, driven and first director (not so much as 
an OWA) and leaving more room to larger spacing other directors.
Like that, the feed impedance is inevitably voted to drop.
The very short spaced director you have is probably an OWA stile 
director, a sort of fake director whose job is to broaden response and 
rising feed impedance. It doesn't have to scare anyone because such 
director is one of the best and smarter ideas to easily achieve in 
practice what's modeled in terms of gain and BW. 
About the 40 dB F/B you report, that's unfortunately a peak (just 
straight back) on a stated frequency and elevation angle.

73,
Mauri I4JMY


> ---------- Initial message -----------
> 
> From    : owner-towertalk@contesting.com
> To      : towertalk@contesting.com
> Cc      : 
> Date    : Thu, 15 Jun 2000 13:58:04 +0000
> Subject : Re: [TowerTalk] T-match?
> 
> 
> "i4jmy@iol.it" wrote:
> > When a multi element yagi is modeled to maximize gain and F/B the
> > driven element feed point impedance actually lowers as well the BW.
> 
> Not necessarily so. Feed impedance is determined by a number of 
things,
> chiefly the length of the boom and element spacing.
> 
> But, boom length is going to be the main factor. You simply cannot 
just
> keep sticking elements on a fixed length boom.
> 
> For example, my 5 element 10 and 5 element 15 have boom lengths of 28
> and 36 feet, with the first Dir spaced so closely to the DE, it's 
scary.
> But, EZNEC models both at almost 16dbi gain over real ground with a 
F/B
> of close to 40 db. And they are killers.
> 
> 73
> Ed




--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com