Re: [SI-LIST] : SMA Impedance Matching
Wed, 4 Mar 1998 14:38:55 -0500


Increase the center conductor clearance to the ground plane to a range of
0.125" to 0.150" depending on your board thickness and number of ground
planes. That will increase inductance in the presense of alot of
capacitance due to the pth and should serve to cancel out the two effects.

Chris Heard
3Com Corp
118 Turnpike Rd
Southboro, MA 01772
508-490-5616 on 03/04/98 01:59:07 PM

To: si-list@silab.Eng.Sun.COM
cc: (Chris Heard/US/3Com)
Subject: [SI-LIST] : SMA Impedance Matching

I installed a Straight Jack Receptacle (SMA female connector) on an
FR-4 PCB. TDR measurements indicate that the impedance goes down to
25-30 ohms where the connector pin actually goes through the board.
I am concerned about this mismatch. Does anyone have any input as to
how I can minimize the size of this discontinuity?
Thanks for any and all help,
Bruce Wallick