Wayne wrote:
When the subject of antenna efficiency comes up, it often involves a
discussion of ground losses on verticals. What about, for example, a
dipole? Could one calculate "power out/power in" by measuring the VSWR
and declaring that everything not reflected was transmitted? It would
seem more accurate to actually measure power out and power in, but that
introduces inaccuracies by having to calibrate the setup. Thoughts?

"Roy Lewallen" wrote in message
...
There's no direct way to measure the total power being radiated other than
sampling the field at many points in all directions and integrating.
"Reflected" power is not power that isn't transmitted. You can find the
power being applied to the antenna by subtracting the "reverse" or
"reflected" power from the "forward" power, but that tells you nothing
about what fraction is radiated and what fraction lost as heat.

Roy Lewallen, W7EL

Thanks for the reply. My dipole example is intended to avoid transmission
line issues by not having one, and the elements are assumed to be reasonably
low loss. If I do some quick back-of-the-envelope calculations, for a VSWR
of 1.3:1, I get an efficiency of about 98.3% (using the equation
1-gamma^2). Assuming a resistance of 1 ohm in the dipole conductors the
efficiency I calculate is about 98.6% (72/73).

Are there any other loss issues missing in this example.