Antonio,
I think the near field probe idea has merit, however you will observe coupling
effects to the cable and human body (if holding probe).
We use to use a Shielded loop antenna to measure Magnetic field emissions in
accordance with VDE 0871 and Mil-Std 461. This would be a better approach with
the antenna fixed on a tripod. Another alternative is the Van Keen Loop (3
axial loop) set. Calibration on thes devices are much more exact that the near
field probes.
Good Luck.
Wolf Josenhans
"Antonio Sarolic" <antonio.saro...@fer.hr> on 11/24/99 05:07:20 AM
Please respond to "Antonio Sarolic" <antonio.saro...@fer.hr>
Sent by: "Antonio Sarolic" <antonio.saro...@fer.hr>
To: emc-p...@majordomo.ieee.org
cc: "Antonio" <antonio.saro...@fer.hr> (Wolfgang Josenhans/MW/US/3Com)
Subject: Near field magnetic probes
Hello group
This discussion list is worth reading and very helpful. I thought I might
put a question that's been bothering me.
I want to measure EM field (H field) originating from GSM base station
antenna (distances 5m-100m), using near field probes for magnetic field.
They are commonly used for locating EM radiation sources on PCBs or leakage
sources.
I see a few problems concerning this measurement.
1. These probes are constructed for sources (PCB, enclosure leakage) that
are very close to the probe tip. Power density of the source falls rapidly
with distance, so the rest of the probe, including connection cable, is
placed in the field that is much lower than close to the probe tip. That is
not the case in the far field. Is the calibration still valid for the
measurements in far field?
2. Also, measurements should be done outside and inside a room. That means
lot of reflections. There must be some cable pick-up. Does this usually add
more field or not?
After all, I think the measurement will not be too accurate, but can provide
the order of magnitude at least. I know I would be better off with the
isotropic probe with optic link, but right now I am interested in near field
probe.
I would like some opinions please. Am I right or am I wrong? Am I missing
something?
Thanks a lot.
Antonio
Antonio Sarolic
Faculty of Electrical Engineering and Computing
Dept. of Radiocommunications and Microwave Engineering
Unska 3, HR-10000 Zagreb
CROATIA
tel. +385 1 61 29 789, fax. +385 1 61 29 717
E-mail: antonio.saro...@fer.hr
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