Re:Conducted Rf Failures...fixes?

[Alex McNeil]

Hi Guys,

Thanks for your responses. 

The ISDN Conducted RF was fixed by choosing an ISDN transformer with
internal CMC (I didn't know they exisetd!)
The LAN was fixed using a twisted pair cable. This was actually a
Technicians mistake as I had already had this requirement on my cable
drawing.

Again, thanks to this group of helpful people.

Kind Regards
Alex McNeil
Principal Engineer
Tel: +44 (0)131 479 8375
Fax: +44 (0)131 479 8321
email: alex.mcn...@ingenicofortronic.com


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Re:Conducted Rf Failures...fixes?

[Kim Boll Jensen]

 Hi Alex and Joe

 Just to add some more information:

 Be sure that the ISDN circuit is in good balance and that the ISDN IC
 have good ground connection and decoupling of supply. The noise can
 affect other nearby circuits. Joe's idea with the caps on ISDN have to
 be checked according to electrical safety standard because of
 restriction on insulation to other circuits.

 The LAN will normally retransmit if a packet is lost. If you use a test
 program which indicates every error in communication, I will suggest to
 make some real life communication to seen if you have a problem at all.

 Best regards,

 Kim Boll Jensen
 Bolls Raadgivning
 Denmark

 j...@aol.com skriver:

  In a message dated 10/8/2002, Alex McNeil writes:
 
 
 
  As I am in panic mode, is there some guidance out there for me e.g.
  is it
  usually a matter of changing the interface IC's or hanging special
  components onto the lines?
 
 
 
 
  Hi Alex:
 
  This test is indeed a difficult one to pass, but in general the
  transformer-type interfaces that you are dealing with are less
  susceptible than some other types.  I have seen ISDN and Ethernet
  interfaces pass this test without the need for extreme measures.  In
  the absence of more specific information about your situation, I can
  offer just a few general guidelines:
 
  1) EN 55024 allows you to use either a CDN or a clamp to induce the
  RF.  Some people find that they get more favorable results with the
  clamp than with the CDN.
 
  2) The interference is applied common mode.  In *theory* your
  transformer coupled interfaces will have fairly good common mode
  rejection, but this can be compromised by a bad layout or by some
  types of surge protection devices.
 
  3) If you have to add some filtering to pass, adding a common mode
  choke is a good first step toward reducing susceptibility.  Adding
  caps from each conductor to chassis ground also helps, especially if
  used in conjunction with a common mode choke, with the choke on the
  line side of the caps.  Note, however, that high value caps can
  interfere with proper operation of the circuit.
 
 
 
  Joe Randolph
  Telecom Design Consultant
  Randolph Telecom, Inc.
  781-721-2848
  http://www.randolph-telecom.com
 
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