That's exactly what I was implying.  The effect would be local to where the
trace and the plane edge coincide, and the radiation would be a function of
field strength (i.e. dc/analog/slow control signals would have very little,
5GHz clock would be very high).

-----Original Message-----
From: Brad Velander [mailto:[EMAIL PROTECTED]]
Sent: Thursday, July 12, 2001 5:55 PM
To: 'Protel EDA Forum'
Subject: Re: [PEDA] 20H rule, Planes etc (Ex: perimeter stitched ground
vi as question)


Bruce,
        this is the manner in which I understand this issue. If I am wrong
please correct me, I don't design antennas for a living and know very little
about such. I do know that I have read certain descriptions of these
problems and the proposed solutions but we all know there are bad solutions
backed up by specific experimentations that prove the solution.

This is the theory that I would apply to the situation.
        The manner that planes do not have noise fields between them is
achieved 'theoretically' because you have coupled your planes together to
near perfection through all of your properly selected, distributed and
positioned power supply bypass capacitors. Effectively reducing the
differential AC potentials between your planes to "0". Now that is the
perfect world which doesn't exist but the real world differences should be
relatively small if you have done your power distribution design correctly.

        Would the application of this to a trace (running parallel to your
plane edge) not be exactly the opposite circumstance? There you have
definite potential difference between the trace and the plane, much larger
differentials then between your two planes. And thus if differentials
between two planes with a little noise causes a dipole antenna effect, why
would a trace with significantly larger differential not cause the same
effect only stronger for the same relative length of the trace against the
plane edge?

        This seems very clear to me but then I don't design antennas so what
do I know. I only know that the article I read about traces and the 20H rule
to plane edges most definitely showed the desired effect in the results
arrived at with the field solvers.

Brad Velander,
Lead PCB Designer,
Norsat International Inc.,
#300 - 4401 Still Creek Dr.,
Burnaby, B.C., V5C 6G9.
Tel. (604) 292-9089 direct
Fax (604) 292-9010
website www.norsat.com


> -----Original Message-----
> From: Bruce Walter [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, July 12, 2001 4:54 PM
> To: 'Protel EDA Forum'
> Subject: Re: [PEDA] 20H rule, Planes etc (Ex: perimeter 
> stitched ground
> vi as question)
> 
> 
(clip)
 
> How well this applies to traces over a plane near the edge of 
> the board, I'm
> not sure, but I would imagine the effect would be local, and 
> would only be
> significant if there were a strong field between the two 
> conductors (poles).
> 

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