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*Subject*: Re: [amsat-bb] Satellite Builder Question*From*: "John M. Franke" <j.m.franke@xxxxxxxxxxxxx>*Date*: Thu, 08 May 2003 13:01:30 -0400*In-Reply-To*: <Pine.GSO.4.44.0305081134440.8218-100000@arctic>

See: http://www.astron.nl/craf/conv.htm John WA4WDL At 11:54 AM 5/8/2003 -0400, you wrote: >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 ---- 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:*Bob Bruninga

**References**:**Satellite Builder Question***From:*Bob Bruninga

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