Re: Surface mount equivalent of clip-on ferrite?

From: Joerg (notthisjoergsch_at_removethispacbell.net)
Date: 10/28/04 

Date: Thu, 28 Oct 2004 20:34:42 GMT

Hi Steve,

>Yes - 99.8 MHz and 102.9MHz - that's with a squarewave signal of 0.5V pk-pk
>at a frequency of 6.144MHz.
>
>
Neither is an integer multiple of 6.144MHz so something else might be
coupling onto that cable. That might make the job a bit easier if you
can find out what it is and what path it takes. Look for integer
multiples, even of bus signals which might not be related to any clocks.

Sniff around for these frequencies. In a pinch you can cut a coax, tape
off the cut end, place a clamp-on ferrite at both ends and snoop across
your circuit with an analyzer or a good receiver connected to the other end.

>>What kind of cable / dummy load did you have connected ?
>>
>>
>
>They had a metre long coax cable with a load attached if I remember
>correctly - I assumed it was 75R, but looking now at the EMC report, it
>lists a 50R load(?!) in the equipment used list (no 75R anywhere)
>
>
Wrong termination and driving the cable hard without the source
resistance being equal to the cable Z will cause a coax to become a
radiator.

Regards, Joerg

http://www.analogconsultants.com

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