amdx wrote:
"Paul wrote in message
...
On Sat, 14 Nov 2009 12:05:21 -0600, wrote:

Hi All,
I'm having a disagreement about the use of this folded dipole calculator
impedance calculator.
http://www.k7mem.150m.com/Electronic...ed_dipole.html
We are using it to calculate the impedance of folded dipoles to drive a
yagi.

Excuse me, but what does such simple dipole calculator have to do with
the calculations for a Yagi feed element ?

I think it all started with the MFJ-1800 that uses a folded dipole, but
there
are many yagis that use a folded dipole as the driven element.
But, I think (now) I understand enough to know why you ask the question.
I think your point is the impedance of dipole feed on a yagi is highly
modified
by the reflector and directors.

Even assuming a single element feed element antenna, playing with the
tube diameter (upper and lower bars) or the number of bars in a folded
dipole will radically change the feed impedance.

Paul


I excerpted this from my latest email to my friend I'm having the
disagreement with. (Might
not even be a disagreement, it could be a miscommunication.)
Excerpt;
"The online calculator takes the (Impedance of a dipole x Ratio). This
gives you the impedance
after folding the dipole.
We still have no idea what the impedance of a dipole is when surrounded by
the reflector and
director. We do know how to change the transformation ratio once we know
what the impedance
of dipole would be in that surrounding."
Mike


Hi,
Even now Yagi-Uda antenna design is empirical business tinkering with it
in the antenna range based on theory plus actual field result.