[SI-LIST] Re: Wacky power plane impedance measurements
- From: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
- To: "'mibrown@xxxxxx'" <mibrown@xxxxxx>,"'chris_landrum@xxxxxxxxxx'" <chris_landrum@xxxxxxxxxx>,"'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 8 Apr 2004 10:09:06 -0600
Chris, The papers I recently posted on measuring the emissions from printed
circuit boards described how to minimize the cable radiation in this kind
of experiment.
If you're interested I can send you the references.
Best Regards
Charles Grasso
Senior Compliance Engineer
Echostar Communications Corp.
Tel: 303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Email: charles.grasso@xxxxxxxxxxxx;
Email Alternate: chasgrasso@xxxxxxxx
-----Original Message-----
From: Brown, Mike (Austin, TX) [mailto:mibrown@xxxxxx]
Sent: Thursday, April 08, 2004 9:53 AM
To: chris_landrum@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Wacky power plane impedance measurements
Sounds like you have signal current on the outside of the coax shield, =
perhaps. Try a ferrite on both coax cables, very near the board under =
test.
Mike
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Landrum, Chris
Sent: Thursday, April 08, 2004 10:03 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Wacky power plane impedance measurements
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.=20
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.=20
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.=20
Thanks.
Chris=20
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=20
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