Thread: New antenna
View Single Post
  #26   Report Post  
Old October 13th 07, 02:28 PM posted to rec.radio.amateur.antenna
Richard Fry Richard Fry is offline
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 440
Default New antenna

"Dave" wrote
and ONE MORE TIME.... define 'equilibrium'. write the equations.
just what is in 'equilibrium' with what??

__________

Art posted his definition in this thread on Oct 11. But no math
to support it.

\\ If he understood Gaussian law then he could have made the Gaussian
antenna which requires an element in equilibrium which means a
FULLWAVELENGTH. I know you dislike the meaning of the term equilibrium but
here it is indispesable. //

What I get from his comments is that Art believes fractional wavelength
radiators are inefficient because they are not in equilibrium, ie, they are
not a full wave length and therefore don't act like a tank circuit (he
says) -- which he believes is necessary for efficient radiation.

I've sent Art several emails with NEC results and math-based discussion
showing that a 1/4-wave monopole working against a 2-ohm r-f ground plane
radiates about 95% of the power applied by a matched source between it base
feedpoint and r-f ground. This is the configuration used by virtually all
commercial AM broadcast stations, and its very high system radiation
efficiency has been proven thousands of times since the earliest days of
broadcasting. Of course that is at odds with the beliefs Art continues to
post here and elsewhere.

In a response to my emails Art seemed to understand, and even thanked me for
"sticking with it." But I guess he was not convinced, because he started
this thread _after_ our email exchange.

Since my discussions with Art I put together a chart showing the groundwave
field generated at 1 km by several, fractional wavelength monopoles at
applied powers from 1-10 kW (see link below). I used a perfect ground plane
in preparing the chart, but the values would be only slightly less with a
2-ohm r-f ground.

ART: Note that the 1 kW field for the 1/4-wave monopole is exactly the peak
field of a 1/2-wave dipole in free space (about 313 mV/m). Taller
monopoles generate more groundwave field, given the same applied power and
r-f ground, because their radiation patterns have more gain in the
horizontal plane and less gain in other directions -- not because they are
more "efficient." All of the monopoles in this chart radiate all of the
power applied to them (100% efficient).

Also note, Art, that a 1/2-wave monopole and its ground image comprise a
full-wave antenna (eg, having your "equilibrium"), yet the 195-degree and
225-degree monopoles produce higher groundwave fields, even though they are
NOT by your definition "in equilibrium."

http://i62.photobucket.com/albums/h8...Radiator10.gif

RF