[SI-LIST] Wacky power plane impedance measurements
- From: "Landrum, Chris" <chris_landrum@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 8 Apr 2004 08:02:44 -0700
Hi all,
I am running an experiment where I am attempting to measure the power plane
impedance of a PCB. The PCB is only populated with capacitors. I am using a
spectrum analyzer to plot the freq response. I have two pieces of 50 Ohm
shielded cable where I have cut the ends to expose the shield and the center
conductor. I have then soldered the shield to a large cap at GND and the
conductor to the other side of the cap at PWR. I have done the same for the
second cable at some arbitray distance from cable #1.
I have noticed that my measurement is EXTREMELY sensitive to cable movement.
The results will also change when I simply touch the N-type adapter of the
SA. I am sure there is a good connection to the PCB, as I have wire tied the
cable to the PCB so as not to allow movement at the points of contact. The
cables may be approx 2ft in length (matched), and I have tried shorter
lengths with the same result. I have also tried higher quality cables.
Is this result due to coupling? Has anyone performed such a measurement
without the varying result? Perhaps someone who has can describe their
set-up.
Thanks.
Chris
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