[SI-LIST] : Return Loss

William Mackillop (Bill.Mackillop@viasystems.com)
Thu, 18 Mar 1999 14:06:46 -0800

Folks,
I have a question on correlating return loss and insertion loss to
impednce.
The ultimate issue may be in assembly, (poor solder joints) but having
said
that here goes.
I have a small 4 layer stripline card. 5mil wide circuits (layers 2 and
3)
12.5mils over their ground (layers 1 and 4) separated by 33 mils.
Two circuits 1.5" and .85" have tested as follows:
1Mhz 25Mhz 150Mhz 300Mhz
Ins loss(.85") -.02 -.05 -.14 -.38
Ins loss(1.5") -.02 -.04 -.14 -.22

Ret loss(.85") -50 -48 -39 -20
Ret loss(1.5") -48 -48 -27 -15

Impede(.85") 74 75 69 89
Impede(1.5") 74 75 73 70

My original thought was that the longer line would be slightly more
capacitive and have a slightly lower impedance but I can't account for
the
numbers I am seeing here.
Any thoughts
Bill
William J MacKillop
804.226.5367 phone
804.226.5511 fax
william.mackillop@viasystems.com

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