[SI-LIST] : SMA Impedance Matching

Jay Diepenbrock (jaydiep@us.ibm.com)
Wed, 4 Mar 1998 20:00:15 -0500

Bruce Wallick wrote:

>>Hello:
>>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, the drop in impedance is due to the capacitance of the via hole to
Ground. Try using an end launch connector, which requires no via.

Jay Diepenbrock

Advisory Engineer
Interconnect Technology & Qualification
IBM Global Procurement, B8UA/061, RTP, NC
Phone: 919-543-8804 Fax: 919-543-3642
Email: jaydiep@us.ibm.com