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Old January 7th 08, 01:59 PM posted to rec.radio.amateur.antenna
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Posts: 106
Default Measuring the fieldstrenght nearby is not reliable.

On 7 ene, 04:25, (Richard Harrison) wrote:
art wrote:

"You did not 'determine" radiated power.....period"

Exactly right. Power in the near field is largely reactive. To determine
radiated power you measure the in-phase volt-amperes with a wattmeter.
The multimeter on the hood maximizes output same as a Bird wattmeter for
practical results, but you hanen`t quantified watts out.

Best regards, Richard Harrison, KB5WZI


Hi Richard,

You can determine radiated power and radiation pattern by near field
measurements (theoretically). Please search for "poynting theorem"
and "Huygens principle", "Huygens Source" or "Fresnel diffraction
theory". Most texts require differential vector calculus.

Because determining radiated power based on E- and H-Field measurement
is generally not feasible for amateurs (and even for many
professionals), I suggested another approach based on E-field
measurements and EM simulation.

As absolute E-field measurement and EM simulation are within the reach
of amateur radio operators, one can both tune for maximum field and
determine absolute radiated power.

Of course you don't know how much power is dissipated in nearby
structures (buildings, etc).

Best regards,

Wim
PA3DJS
www.tetech.nl
 
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