# R: Satellite Builder Question

• Subject: R: [amsat-bb] Satellite Builder Question
• From: "i8cvs" <domenico.i8cvs@xxxxxx>
• Date: Fri, 9 May 2003 00:39:13 +0200

```Bob,

You will find the volt/m definition and the equations to calculate it
in the following document

Federal Communication Commission
Office of Engineering & Technology

EVALUATING COMPLIANCE WITH FCC
GUIDELINE FOR HUMAN EXPOSURE TO

SUPPLEMENT B
(Edition 97-01)
to
OET Bulletin 65 (Edition 97-01)

You can get the above document  from the ARRL

73" de i8CVS Domenico

----- Original Message -----
From: Bob Bruninga <bruninga@usna.edu>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, May 08, 2003 5:54 PM
Subject: [amsat-bb] Satellite Builder Question

> 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
>
>
> ----
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