How would one go about accurately measuring low frequency fields say at 10
kHz where the far-field even at lambda/6 is 5000 meters?
Bob Heller
3M EMC Laboratory, 76-1-01
St. Paul, MN 55107-1208
Tel: 651- 778-6336
Fax: 651-778-6252
=========================
"Price, Ed"
<ED.PRICE@cubic.c
om> To
Sent by: emc-p...@ieee.org
owner-emc-pstc@ie cc
ee.org
Subject
RE: ??? RE: ??? RE: Near field
06/23/2005 11:24 H-field measurement.
AM
> -----Original Message-----
> From: Bob Richards [mailto:b...@toprudder.com]
> Sent: Thursday, June 23, 2005 7:06 AM
> To: emc-p...@ieee.org
> Subject: Re: ??? RE: ??? RE: Near field H-field measurement.
>
> Ken,
>
> I believe you are correct. There should be factors for this
> loop antenna from Emco that convert the raw reading (in dBuv)
> to a magnetic field level (like dBuA/m).
>
> The spectrum analyzer does NOT read in dBuv/m as he seems to
> suggest, it only reads in dBuv or dBm, but some analyzers do
> allow factors to be entered so the display will be in useful
> units. I prefer not having the analyzer apply factors. Less
> chance for errors that way, IMHO.
>
> Bob Richards, NCT.
EMCO (ETS) shows generic correction factors for the 6502 at:
http://www.ets-lindgren.com/productpage.cfm/model/6502/producttype/Antennas
They have a pair of charts for correcting the antenna output (in dBuV) to
units of electric field (dBuV/m) or magnetic field (dBuA/m).
I don't like the practice of a factor for converting loop output voltage
directly to dBuV/m, because it is making the assumption of far-field
conditions (377 ohms, and an H-field to E-field conversion of +51.5 dB).
The 6502 is a shielded loop, and responds to the H-field, no matter where
you place it. You can accurately derive the E-field from the H-field only
when you are confident of far-field conditions.
Ed Price
ed.pr...@cubic.com WB6WSN
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Is Our Specialty
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