Dear EMC experts,
For a beginner like me this is really a treasure. I get answers to all
my questions. I am thankful to everyone who replied me.
Today I ran radiated emission testing for an USB device in fully
anechoic 3 meter chamber. In horizontal polarization the unit failed at 72
MHz. Then by adding a ferrite core on the USB cable the unit found to pass
with good margin. But the observation is like this:
When the ferrite core is near to the EUT, test fails and the result
is almost similar to the test without a ferrite core. Then I tried by moving
the ferrite core gradually towards the other end of the cable. I noticed that
as the ferrite core is slowly moved away from the EUT, the emission level also
gradually reduced and when the ferrite core was kept at the farthest point of
the cable (cable length is about 1 meter) the emission was minimum. In my
previous scans (in other devices) I don't remember a ferrite core helping in
horizontal polarization.
So what is the logic behind this? I request you all to clarify me.
Thanking you all sincerely
K.Balasubramanian
Sr.Engineer, Hardware.
