[Antennaware] FW: FW: Fwd: Modelling yagi split DE

[Charlie Ocker via Antennaware]

Hi Matt,

The gain is free space.

I am 100% on board with the merits of hairpin matching.  My other 
homebrew yagi, a 5el 15m, is hairpin matched.

I have another optimization set of results for my 20m yagi that uses the 
hairpin match.  Overall, it is slightly better in gain and F/R.  It 
looks like an OWA, too, with D1 close to DE.  The vswr bandwidth is 
excellent, covering the whole 20m band less than 1.3 to 1.

I have played around with YO enough to observe that no matter what 
parameters I adjust, or the weights that I apply to them, that gain 
seems to always occur.  One of my runs that gave very good results, I 
set the gain weight to 5%, the F/B at 50%, and SWR at 45%.

Regarding your 20m stack - nothing wrong with that setup!  Paul, W0AIH, 
uses a 4 stack of 204BA's as his main 20m antenna.  They work very well.

I found a technical paper on the internet written by a university 
professor that describes very well the math behind the hairpin (beta) 
match, and how to use a modelling program to estimate the parameters 
needed.  I wrote a spreadsheet that uses these equations and methods, 
and I can quickly zero in on a hairpin match using the "Source Data" 
feature of EZNEC.  I would be happy to share it if there is any interest.

73,
Charlie  N9CO

On 7/9/2014 10:38 PM, Matt wrote:
> FB Charlie - understand you want the 50 ohm match.   I have a pair of
> stacked 4 element 20m beams on 26ft booms (yea - I know it's too short but
> it's what I have...)  I optimize my 3-el or larger Yagi's for -25J ohm
> reactance and then back off when the impedance starts to go south of about
> 20 ohms.   This seems to work very well for beta match, which is my
> preferred method of feeding.   I like the fact that the beta grounds both
> sides of the DE (I have some element tips with holes burned right through
> them from lightning strikes - no other consequence).  I feed everything with
> baluns so beta is not an issue.
>
> With respect to optimization, I generally optimize for F/B over bandwidth
> and forward gain usually falls right into place.  You don't mention if your
> forward dbi is over real ground or free space ???
>
> Matt
> KM5VI