Muriel,
interesting question. Considering common mode noise on the load wires: With
the load at the end of the wires, but not grounded, you have a monopole
antenna. With the load wires terminated into a filter (I'm assuming low-Z to
GND) you have a loop antenna. I ran a quick simulation using NEC-2 at 100 MHz
using a wire length of 13 cm for an inverted-L configuration (3 cm vertically
and 10 cm horizontally). The loop has dimensions are; 3 cm vertically, 10 cm
horizontal, and 3 cm back to GND. Given 1 mV and a 10 ohm source impedance the
loop radiates 19 pW. Given the 1 mV source the monopole radiates 47 fW. A 26
dB difference given these parameters. Placing the power supply outside through
filters is the winner for the most radiation, given these randomly selected
parameters.
Are you orienting the power supply on each of the three axis? And rotating it
at each? This is what I have found inconvenient about TEM cells.
Dave Cuthbert
Micron Technology
From: Muriel Bittencourt de Liz [mailto:[email protected]]
Sent: Thursday, February 20, 2003 11:52 AM
To: EMC-PSTC List
Subject: About Radiated Measurements
Group,
I have a doubt concerning radiated emissions measurement:
- For radiated emissions measurement of switched mode power supplies using a
TEM cell, should I leave the loads of the supply inside or outside the
cell?? My TEM cell have filtered connections for DC loads.
Thanks in advance for your help.
Best Regards,
Muriel
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