2) Through hole connectors have barrels in the pcb . Which has the
largest coupling barrel to barrel or pads to plane? Is there any
formula for calculating these 2 coupling phenomena in multi layer
boards?
3) When performing a differential TDR on a 2 millimeter connector (Berg
HS), I see the barrels in the board appear to be 40 ohms. This clearly
is 40 ohms because it appears on both sides of the connector and each
pcb is a different thickness. The trace impedance of 40 ohm is 125 pS
long for one board (62 mils thick) and the other board is 210 pS (100
mils thick). In between it does go to 50 ohm. Has anyone else seen this.
Chris Knapton