Re: [SI-LIST] : EMI due to fans (fwd)

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Thu Oct 12 2000 - 11:37:54 PDT


Sunil,

I tend to agree with somebody here, who suggested your probe actually
picks up noise. I don't see how EMI from fans can badly affect twinax
cable, unless your Ground Connection is re-e-e-eally screwed up (and it
takes some screw-up plus some ingenuity and luck....).

Mike.

George Borkowicz wrote:

>
>
> One more per cent. Try to replace the fans with a resistive load
> of the same power (bulbs, power resistors, what have you) right
> at the fan end of the fan wires.
>
> gjb
>
> -----Original Message-----
> From: Sunil Kumar [SMTP:sunilb@cdotb.ernet.in]
> Sent: Thursday, October 12, 2000 2:42 AM
> To: si-list@silab.eng.sun.com
> Subject: [SI-LIST] : EMI due to fans (fwd)
>
> Hello everybody.
>
> I am measuring cycle-to-cycle jitter in clock in a system, where
> clock
> (PECL, 50MHz) is going from one PCB (card) to other through
> twinax
> cable. In the second card clock is converted into TTL and then
> distributed
> to various ICs. I am looking at the clock just before the
> PECL-to-TTL
> convertor. Both the cards are in the same backplane. The system
> is
> equiped with a set of fans for cooling, which are kept below the
> card
> frame. Now what I have observed is, when the fans are not on,
> jitter is
> much much less in comparision of the jitter when fans are on. I
> think, the
> fans are generating EMI, which is disturbing the planes in the
> backplane
> and the cards, and hence jitter is increased. Any explanations?
>
> One more thing which I have observed is, the PECL-to-PECL clock
> fanout buffer (no PLL inside) is reducing jiiter (with fans off),
> i.e.
> jitter at input is more than that at output. Can anybody explain
> this?
>
> Is there any PECL-to-TTL clock fanout buffer which adds very low
>
> jitter? The PECL-to-TTL buffer which I am using, is adding lot's
> of
> jitter.
>
> Thanks
>
> Sunil Kumar
> Senior Research Engineer
> ATM Group
> C-DOT
> Bangalore-560052
> INDIA
>
>
>
>
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