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[email protected] · December 13th 10, 06:02 PM posted to rec.radio.amateur.antenna

Registered User wrote:
On Mon, 13 Dec 2010 00:13:10 -0000, wrote:

Registered User wrote:
On Sun, 12 Dec 2010 17:32:53 -0000, wrote:

Registered User wrote:

Efficiency is a measure so it must have one or more dimensions

Efficiency is a ratio usually expressed as a percentage and has no dimensions.

The efficiency of an antenna is the radiated power divided by the input
power.

There are two dimensions in the calculation, radiated power and input
power. Although the units of measure associated with the dimensional
data may cancel the dimensional metadata doesn't.

x power/ y power = x/y

The units cancel to form a dimensionles, unitless, ratio.

This is grade school math.

unitless yes and in the example given no metadata is provided. The
result of the calculation is just a meaningless number.

What of the equation :
x units of radiated power / y units of input power
The units cancel but the metadata doesn't. The result is a number that
describes the ratio of radiated power to input power.

2 watt / 10 watt = 0.2

No "metadata".

If the 2 watts is the radiated power of an antenna and the 10 watts is the
input power, the antenna efficiency is 0.2 or 20% since efficiency is normally
expressed as a percentage.

If the 2 watts is the output power of some circuit and the 10 watts is the
input power, the circuit has a gain of 0.2 or -7db.

If the input energy to a heat engine is 10 joules and the output energy is
2 joules, the efficiency of the engine is:

100 * (2 joule / 10 joule) = 20%

--
Jim Pennino

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