"Wayne" wrote:
"Steve" wrote in message ...

On Wed, 22 Oct 2014 17:36:31 +0100, FranK Turner-Smith G3VKI wrote:

"Wayne" wrote in message
...
"gareth" wrote in message ...
Try this ...

http://farside.ph.utexas.edu/teachin...es/node94.html

This is one of a series of lectures by a prof at Texas Uni.

In fact, if you go right back to the home page of
http://farside.ph.utexas.edu/teaching,
this leads to a most excellent revision of the necessary EM theories,
and,
briefly glancing thereto, the post grad stuff even exceeds my current
interest and knowledge.

I'm fairly sure now that this area is where I came across the governing
formula that I alluded to recently in this NG when doing my own
revision previously in 2005, although the URLs and lecture node numbers
have changed since then.

When I get time, I'll browse through the links.

However, back to your original assertion that your theory has short
antennas as being inefficient compared with longer antennas (I'm
assuming you are talking half wave dipoles and such).

If 10 watts is delivered to a short antenna, where does it go if it is
not radiated just as well as 10 watts delivered to a long antenna?

Dissipated as heat?

# Probably proportionately more will be lost as heat as a very short
# antenna will be a low impedance, therefore current, driven job and I sq*R
# losses within the antenna will play their part. Apart from those
# additional losses, it should radiate all that is left, ... I think.

Actually no. The loss resistance tends to be dwarfed by the radiation
resistance, so losses in the antenna are not the problem.

The problem is matching. A small antenna has a narrow BW so you tend to
need a matching system. That is where the losses will be, plus in any
feeder.

Of course, if you only need a narrow BW and can arrange a low loss feeder
plus load the pa correctly, then pa is happy, low feeder loss, the RF gets
to the antenna.

The antenna RrRL so antenna loss is low.

RF has only one place left to go, to be radiated.




But I^2 R losses are not part of the theory Gareth presented