[SI-LIST] Re: Telephone Circuit EMC issues
- From: Bill Wurst <billw@xxxxxxxxxxx>
- To: Saril <saril_k@xxxxxxxxx>
- Date: Wed, 07 Jan 2009 16:01:01 -0500
Saril,
You haven't provided much information to go on. If I understand your
problem correctly, you have a conducted emissions problem which I'm
assuming is measured at the power Line Impedance Stabilization Network
(LISN). Then, when you connect the telephone line the conducted power
emissions increase.
I can only guess, but my hunch is that conducted emissions on the
telephone line are radiating and being picked up by the power cord. You
might try re-arranging the telephone cord to see if that has an effect.
I doubt that the filter capacitors on the Tip & Ring could increase
the common-mode noise on the digital side, but if not implemented
properly (noisy ground connection and so forth) could certainly increase
conducted emissions on the telephone line.
Hope this helps.
Regards,
-Bill
/************************************
/ William C. Wurst, PE /
/ billw@xxxxxxxxxxx /
/ Advanced Electronic Concepts, LLC /
/ www.aec-lab.com /
************************************
================================================================
Saril wrote:
> Hi All,
> I'm working on a dial up modem board. There are some conducted emissions. I
> have to do some wrok around to get it suppressed.
> we have two capacitors (0.1uF)Â as shown below, connected from the TIP and
> RING to the Digital ground.
> Â
> TIPÂ Â ------------------------
> Â Â Â Â Â Â Â |
> Â Â Â Â Â Â |
> Â Â Â Â Â Â Â _ C1
> Â Â Â Â Â Â Â |Â Â Â Â Â Â 0 Ohm Res
> Â Â Â Â Â Â Â Â --------^^^^--------- DIG_GROUND
> Â Â Â Â Â Â |
> Â Â Â Â Â Â Â _ C2
> Â Â Â Â Â Â Â |
> Â Â Â Â Â Â |
> RING ------------------------
>
>
> These capactiors are provided as per the modem chip vendors advice. when the
> telephone line is connected to the modem the emissions seems to be
> increasing.
> Â
> Does this capactors have any role on increasing the common mode noise on the
> digital side and causing the emmission to aggravate.
> Â
> Thanks in advance.
> Â
> Regards,
> Saril Kaiprath
> Hardware Design Engineer
>
>
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