On 4/11/2009 12:52 AM, Joe Subich, W4TV wrote:
> Since the cage dipole is shorter than a normal
> half wave dipole (L/D ratio), the only way it can show gain
> is through an increased current.
Increasing the current while maintaining the distribution of current
along the antenna does not produce "gain" provided that the applied
power is held constant.
Directive gain can be realized only if the distribution of current along
the antenna is altered in some way. Changing the current distribution
changes the far-field pattern and the directivity.
Of course, this doesn't happen to any significant degree in the case of
a cage dipole .
While the current distribution along a dipole does vary slightly with
(l/d), the resulting changes in gain are in the realm of 0.001's of a dB
and of no practical interest.
> All of this is basic electromagnetics and is discussed
> fully by Kraus and others in the standard antenna texts.
Absolutely.
Those texts also contain mathematically rigorous solutions for the
integral equations which describe a dipole constructed of finite
diameter cylinders. No modelling, no NEC, no "time diversity"
doublespeak; just James Clerk Maxwell plus a bit of the calculus.
Would anyone find it even remotely plausible that the gain of a dipole
were to decrease by 6 dB if a solid cylinder were to be substituted for
a wire approximation to that cylinder?
The standard applied to those who would rewrite the laws of physics is
that "Extraordinary claims require extraordinary evidence."
There's nothing particularly extraordinary about the evidence that's
been offered in this case; if anything the evidence in quite pedestrian.
'Nuff said.
73,
Mike K1MK
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|