Bob, the circular plastic (delrin) washer was small enough to fit inside the four SMA ground posts. The only pin that went through the washer hole was the center pin. I used this because the SMA appeared capacitive. Raising the SMA center pin off of the via added a little series inductance. The result on the TDR was that the signal started to rise above 50 ohms before it took a capacitive dip. When the rise equals the dip, you have achieved the best possible match (somewhere I read that this is called a doublet). If you have access to a TDR with a very fast risetime, I would suggest trying the concept by not soldering the SMA to an existing card, and moving the connector in and out of the card while viewing the TDR waveform. If the holes are not too sloppy, you should be able to see the difference easily. It was around '89 when I did the board compensation stuff, and I can't remember what the stackups were. I don't remember if the unused vias were removed or not, and I don't know how many layers I was dealing with. My suggestion to the person on the SI List overcompensated his situation, and he wound up with his SMA launch looking inductive. Referring to your second paragraph, you misunderstood my suggestion, which was to remove the copper (increase the antipad) all the way out to where the antipad almost touched the inside corners of the four ground pins. The ground pins were soldered on all sides to the plane, as usual. This makes for a very large antipad, and I suspect it was in the days before we started removing the unused vias for signal integrity purposes. Richard Ellison 214-544-1920 bus 214-544-1924 fax ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu