Re: [SI-LIST] : EMI

khardin@lexmark.com
Fri, 31 Oct 1997 15:01:42 -0500

Derek,
I agree with you that some amplitude modulation of harmonics can
be detected by any nonlinear circuits in a system. However, if
you frequency modulate with a periodic modulating profile
and sufficient frequency, the harmonics are constant amplitude.
This fact means that you meet the letter and intent of the
testing. One point that is misunderstood is that an SSCG
peak reading is the same as QP readings. This may not be
true for jitter of a clock.

The only complaint that I have heard over the last 4
years is that in an automobile a handheld receiver will break
squelch more often. This is true because the SSCG covers greater
frequency ranges and the car electronics are in very close
proximity. However, the level of interference
does to disturb any intended signal that is trying to be picked up.

Since using this technology we have answered these kinds
of questions for a long time. I am always glad to here the
tradeoffs of using this technology.

Regards,
Dr. Keith Hardin
Senior Engineer
MS:D33L/032-2
Lexmark International Inc.
740 New Circle Rd NW
Lexington, KY 40511

Lfresearch%aol.com@interlock.lexmark.com
10/31/97 01:39 PM

To: Keith Hardin@Lexmark, esayre%nesa.com@interlock.lexmark.com
cc: si-list%silab.eng.sun.com@interlock.lexmark.com
bcc:
Subject: Re: [SI-LIST] : EMI

Hi chaps,
this topic lasted longer than I thought, and generated more responses.....
My original objection to the SS approach stems from experience in the EMC
business. While it may seen sufficient that the amplitude of an undesired
signal is reduced, what often occurs is that the CW nature of a clock
harmonic ( is a nuisance agreed, but ) does not corrupt circuits. However,
when you apply modulation, the RF gets the signal into a circuit, and
somewhere there is a demodulator ( intentional or otherwise ) that
demodulates the RF and responds to the modulation.
I guess in a nutshell, just killing the amplitude of a signal will get you
through a test, but may not meet the intent of the testing, which is not to
interfere with other systems. This is the EMC engineers point of view, I'm
open to others...

Best regards,
Derek Walton.
L F Research EMC Design and Test Facility