This is a multi-part message in MIME format.
Iain,
I have forwarded your question to Ed Hare of ARRL, below or attached is his
response.
Regards,
Dave Garnier
I can jump in, but this sure is a mess.
There are differences between "reactive" and "radiating" near field regions,
where one, essentially defined by lampda/2pi, there is E or H field field
strength, it is reactive in that energy is put into the field and then taken
back, with only a portion radiated. There is the radiating field region,
where the fields are radiated, but one is not equidistant from all parts of
the antenna, so the relation between E and H vary over space, with non-planar
fields; standing waves of fields; varying phase relationships between E and H
and the probability that E/H will not be 377 ohms.
For a few examples:
http://p1k.arrl.org/~ehare/bpl/ppt/Hare_extrapolation_draft.ppt
I will correspond with him.
Do either of you want to be cc's?
Ed Hare, W1RFI
ARRL Laboratory Manager
225 Main St
Newington, CT 06111
Tel: 860-594-0318
Internet: [email protected]
Web: http://www.arrl.org/
Member: ASC C63 EMC Committee
Chairman: Subcommittee 5, Immunity
Chairman: Ad hoc BPL Working Group
Member: IEEE P1775 BPL EMC Committee
Member: IEEE, Standards Association, Electromagnetic Compatibility Society
Member: IEEE SCC-28 RF Safety
Member: IEEE EMC Society Standards Development Committee
Chairman, BPL Study Project
Member: Society of Automotive Engineers EMC/EMR Committee
Board of Directors: QRP Amateur Radio Club International
_____
From: [email protected] [mailto:[email protected]] On Behalf Of Iain Summers
Sent: Wednesday, August 02, 2006 2:25 AM
To: [email protected]
Subject: Near field/Far field what is D.
There are various references and opinions as to what constitutes the near
field far field boundary. The common one from antenna theory is 2D^2/lambda
where D is defined as the largest aperture of the antenna.
Has anyone researched what the limitations of this formula are? I am
interested in the far field boundary between 1-30MHz for large loops of wire.
In terms of a loop if this formula is applicable is D the circumference or
diameter of the loop.
Thanks,
Iain
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--- Begin Message ---
I can jump in, but this sure is a mess.
There are differences between "reactive" and "radiating" near field regions,
where one, essentially defined by lampda/2pi, there is E or H field field
strength, it is reactive in that energy is put into the field and then taken
back, with only a portion radiated. There is the radiating field region, where
the fields are radiated, but one is not equidistant from all parts of the
antenna, so the relation between E and H vary over space, with non-planar
fields; standing waves of fields; varying phase relationships between E and H
and the probability that E/H will not be 377 ohms.
For a few examples:
http://p1k.arrl.org/~ehare/bpl/ppt/Hare_extrapolation_draft.ppt
I will correspond with him.
Do either of you want to be cc's?
Ed Hare, W1RFI
ARRL Laboratory Manager
225 Main St
Newington, CT 06111
Tel: 860-594-0318
Internet: [email protected]
Web: http://www.arrl.org/
Member: ASC C63 EMC Committee
Chairman: Subcommittee 5, Immunity
Chairman: Ad hoc BPL Working Group
Member: IEEE P1775 BPL EMC Committee
Member: IEEE, Standards Association, Electromagnetic Compatibility Society
Member: IEEE SCC-28 RF Safety
Member: IEEE EMC Society Standards Development Committee
Chairman, BPL Study Project
Member: Society of Automotive Engineers EMC/EMR Committee
Board of Directors: QRP Amateur Radio Club International
_____
From: [email protected] [mailto:[email protected]]
Sent: Wednesday, August 02, 2006 10:24 AM
To: [email protected]; Hare, Ed W1RFI
Cc: [email protected]
Subject: RE: Near field/Far field what is D.
This is fantastic theory if you are doing this half way between the earth and
the moon. If not, you need to add the ground effect and a few other minor
modifications into the formula due to wavelength, etc. You also need to
include wire-to-wire spacing, etc. Wow. Talk about over simplification.
Regards,
Wayne
(302) TN633-8490
_____
From: Garnier, David S (GE Healthcare) [mailto:[email protected]]
Sent: Wednesday, August 02, 2006 10:06 AM
To: Hare, Ed W1RFI
Cc: [email protected]
Subject: FW: Near field/Far field what is D.
FYI - Maybe you would like to comment to the author
Note the reference to PLT
dave garnier
David Garnier
e GE Health Care
___________________________________________
David S. Garnier
Senior Technician
Functional & CT Engineering
3000 N. Grandview Ave - M/S W-1250
Waukesha, Wi. 53188
Tel: 262.312.7246
Cel: 414.899.7580
_____
From: [email protected] [mailto:[email protected]] On Behalf Of Iain Summers
Sent: Wednesday, August 02, 2006 7:32 AM
To: [email protected]
Subject: Re: Near field/Far field what is D.
John thanks,
I am aware that the boundary is a smooth transition and the main reason for
wanting to know is to do with some subjective analysis of powerline
telecommunications measurements that I have completed.
There are various papers that state that the attenuation of E with distance is
1/distance(d) in the far field and some combination of 1/d, 1/d^2 and 1/d^3 in
the near (or very near) field.
I have conducted measurements from 1-30MHz in a densely populated housing
estate, in a semi rural college and at a semi rural house that has no objects
to reflect the field strength back. I have plotted all of the graphs and
included curves for 1/d^0.5, 1/d, 1/d^2, 1/d^3 and I am now in the process of
correlating them.
What I'd like to know is how large the measurement errors are. eg I have used a
loop (which is the recognised method) and then converted to E for comparison to
others results by using E/H=377 which is only true in the far field. I though
it would be useful to determine what the results might be if E/H approached
3000 or 30 say and for that thought I'd use the point source formula
lambda/2*pi and also 2*D^2/lambda to determine how near or far the boundary
might be.
Sorry that is a bit of a ramble but that's the background to it.
You mentioned that D might be an area which was my initial thoughts as it is
quoted for use as an aperture and therefore may not be wholly appropriate to
use in the instance of the source being a large loop in the horizontal plane.
The overall aim of my PhD is not to come up with any answers per se but to
explain to others who quote EMC theory in relation to PLT measurement. There
are lots of assumptions but no one aver states "the answer is x and by the way
that is + or - 50%". There are lots of people measuring E in dBuV to 2 decimal
places with no mention of the errors in their measurements. This is fine for
compliance if everyone does the same thing but some people are trying to
predict interference based upon these results.
Thanks,
Iain
----- Original Message -----
From: "John Woodgate" < <mailto:[email protected]> [email protected]>
To: < <mailto:[email protected]> [email protected]>
Sent: Wednesday, August 02, 2006 8:59 AM
Subject: Re: Near field/Far field what is D.
In message < <mailto:001c01c6b604$c0ed2810$6401a8c0@homepc>
001c01c6b604$c0ed2810$6401a8c0@homepc>, dated Wed, 2 Aug
2006, Iain Summers < <mailto:[email protected]>
[email protected]> writes
>There are various references and opinions as to what constitutes the
>near field far field boundary. The common one from antenna theory is
>2D^2/lambda where D is defined as the largest aperture of the antenna.
There isn't a sharp boundary. What you take as the boundary depends on
why you want to know where it is, and you don't tell us that.
For example, you might decide that you want to know where the phase
angle between E and H is only 1 degree. Or is 45 degrees. Or more.
>
>Has anyone researched what the limitations of this formula are? I am
>interested in the far field boundary between 1-30MHz for large loops of
>wire.
Large compared with the wavelength at 1 MHz? That's large indeed!
>In terms of a loop if this formula is applicable is D the circumference
>or diameter of the loop.
Or maybe the area?
--
OOO - Own Opinions Only. Try <http://www.jmwa.demon.co.uk>
www.jmwa.demon.co.uk and <http://www.isce.org.uk> www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
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