Dear EMC Gurus,
I completed my pre-scans for an intentional radiator (13.56 MHz) in a
3 meters fully anechoic chamber and found that the emission are well within
the Class B limits. The emission @ 108.48 MHz (8th harmonic) was around 35.8
db, @ 135.6 MHz (10th harmonic) was about 24 db, @ 162.72 MHz (12th harmonic)
was about 29 db and @ 244.08 MHz (18th harmonic) was about 37.5 db. 3 samples
were tested and the results were similar for all the 3.
But when another sample of the same model was tested by my counterpart
in the 10 meters OATS (at USA) the results are differing. Emission @ 244.08
MHz is reported about 37.10 db, @ 162.72 MHz is 31.1 db, @ 135.6 MHz is 27.2
db and the device failed to meet Class B limits.
The test setup is very simple and it is just the 12 volts d.c. output
of a variable d.c power supply output connected to the device. The power
supply used by me and by my counter part are not same but similar. I tried
separately with a shielded cable and with an unshielded cable and the results
were almost similar. My counterpart used only a unshielded cable.
Now it is great puzzle for us. What is wrong and where? Apart from the
device being tested, the power supply and the cable used there are no other
variables involved in the test set up. What other factors we should compare
between both the testing? I request you all provide your valuable feedback.
Sincerely
K.Balasubramanian
Sr.Engineer, Hardware.
