Topband: Antenna Impedance vs efficiency

[Ford Peterson]

Ken wrote:

> Hi Ford,
> 
> There have been a lot of responses to your post. Most of them addressed 
> the issue of the impedance of free space. I would like to comment on 
> your usage of water flow in a garden hose as an analogy for RF 
> propagating through transmission lines.
> 
> The use of analogies to help visualization of invisible phenomena can 
> both help us understand and it can also mislead us. If RF energy 
> transmission  through a transmission line depended on the delivery of 
> electrons from one end to the other, with more electrons delivered being 
> better, then your analogy would work better.

...snip...

Ken, and others...

When I gave that seminar on SWR to the local club, my biggest concern was trying to provide a visual image of what is happening with a transmission line, reflections on the line, and the resultant loss of signals due to the line losses.  The biggest trouble with this audience is their virtually complete lack of understanding.  Most of the guys are hamshack on the belt clip types, running mobile VHF gear and the like.  With all of its technical imperfections, the garden hose analogy allowed me to explain to these young recruits, in language they understood, why lines generally work better when matched with load and source impedances.

I suspect I could have taken a more exacting approach (I took careful note of the eyes glazing over when presenting the math) but in the 20 minutes allocated, the garden hose visual worked, without having to explain Nepers, dB, or the wonders of real and imaginary impedances.

I appreciate the many thoughtful responses to my query about the interface between the so-called "impedance of free space" and our seemingly low impedance antennas.  Once again, Topbanders unite to clarify and hone our understanding of the magic of RF.  This reflector is an excellent resource.  Where else can a fella pose a naive question and get thoughtful answers?

Thanks

Ford-N0FP
ford at cmgate.com