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*Subject*: [amsat-bb] Satellite Builder Question*From*: Bob Bruninga <bruninga@xxxxxxxx>*Date*: Thu, 8 May 2003 11:54:53 -0400 (EDT)

RF Field Strength Experts? I still cannot get a consistent answer from NASA and other "experts" about Field Strengths or how they calculate them. THey specify limits in terms of X Volts/Meter. My question is what "meters" are they referring to and where? Distance from the source? or "field Strength" at the source? One bureaucrat said they mean "Field strength" at a normalized distance of 1 meter. But I cannot find this anywhere in writing. We have weekly meetings with NASA folks and after 3 months, they still do not have an answer as to what our safe limits are or how they calculate them (other than saying we are over them)... I can calculate "Volts/meter" at the source by simply taking my 435 MHz 2 Watt transmitter into a 50 Ohm monopole 1/4 wave antnena (18 cm), and I compute a voltage on the antenna of 50v/m over the 18cm long whip. But how to normalize that to a field strength 1 meter away or any other distance? Or do they simply use the 1/r^2 isotropic approach? There I would say the surface area of a 1m radius sphere is 4Pi square meters over which my 2 watts is spread. THus I get 0.16 Watts per meter squared. The most power that could induce into a wire would be a 1/4 wave wire (.18 m) so I multiply and get a field strength of 28 milliwatts per meter. Convert to volts (assuming a 50 ohm system) and get about 1.2 volts per meter at 1 meter from the antenna. This would go down as 1/r^2 in the far field beyond about 3 wavelengths.. What is the RIGHT way to do these calculations? Bob, WB4APR ---- Sent via amsat-bb@amsat.org. Opinions expressed are those of the author. Not an AMSAT member? Join now to support the amateur satellite program! To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**Follow-Ups**:**Re: Satellite Builder Question***From:*John M. Franke

**R: Satellite Builder Question***From:*i8cvs

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