Do you have a grounding problem between the signal source and the Spectrum Analyzer? Tom Dagostino Teraspeed Consulting Group LLC Device Modeling Division 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 tom@xxxxxxxxxxxxx <mailto:tom@xxxxxxxxxxxxx> Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 http://www.teraspeed.com Teraspeed (SM) is the service mark of Teraspeed Consulting Group LLC -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Istvan NOVAK Sent: Thursday, April 08, 2004 5:41 PM To: chris_landrum@xxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Wacky power plane impedance measurements Chris, You mention spectrum analyzer... was the source a built-in tracking generator? Or did you mean network analyzer? Beyond the points that other people already pointed out, you may experience sensitivity to cable location if the IF bandwidth is unnecessarily wide, and/or if accidentally you mix up the power and ground connections inj the two cables. This means if you connect accidentally the braid from the source cable to the center of the receive cable. I hope this helps. Istvan Novak SUN Microsystems ----- Original Message ----- From: "Landrum, Chris" <chris_landrum@xxxxxxxxxx> To: <si-list@xxxxxxxxxxxxx> Sent: Thursday, April 08, 2004 11:02 AM 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. > 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 > > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl > > List technical documents are available at: > http://www.si-list.org > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu