One of the more interesting scientific studies I have seen on this subject
was published in the proceedings of the PCB Design Conference, and I have
never seen it reprinted anywhere else. The author built boards with every
different configuration of pairs of parallel traces separated by grounds and
open spaces, and then drove them at different frequencies to measure
crosstalk.

For example:
G=ground, o=open space, tested at 100KHz
-++-    -65
-+o+-   -75
-+G+-   -89
-+oo+-  -80
+-+-    -65
+-o+-   -75
+-G+-   -89
so adding a space between the pairs resulted in 10db reduction in crosstalk,
but making it a ground reduced an additional 14db

I can't reproduce all of the tables here, and I only saved the "results"
pages so I don't know which year it was (sorry), but if you seriously want
to find it I can tell you it was on page 146, course number 105 called
Analog Design and it was NOT in 1993, 1995, 1996 or 1999

Good Luck
Jack

                -----Original Message-----
                From:   Hawes, Adam

                        Recently, I have come across an increasing number of
engineers who
                wish to have certain tracks on multilayer PCB's shielded by
ground traces
                running adjacently. It seems to be a case of jumping on the
bandwagon to me
                because we never used to do this until about 12 months ago.

                Adam Hawes
                PCB Design Eng.
                GenRad Ltd.

                Tel: 0161  491 9290
                Fax: 0161 491 9106