From: Ron Miller ([email protected])
Date: Mon Oct 23 2000 - 11:24:24 PDT
Hi Jeff
As you say there is current in the ground plane. There are many sources for
this current so for critical signals stay away from it. Measurement implys that
accuracy is important so decouple stray sources. That means do not connect the
ground unless needed. For differential signals ground is not needed.
Ron
> -----Original Message-----
> From: Loyer, Jeff W
> Sent: Monday, October 23, 2000 8:27 AM
> To: 'Ron Miller'; 'Bob Lewandowski'; Ken Taylor
> Cc: [email protected]
> Subject: RE: [SI-LIST] : Re: Diff probes for tdr.
>
> OK, now I'm confused (nothing new here, though)...
>
> Every TDR literature I've seen (TDA, Bogatin, Agilent) clearly shows
> connecting the ground of each TDR probe to the motherboard ground when
> performing differential impedance measurements. This agrees with my
> perception of the differential model, where the capacitance between the
> trace and motherboard ground can be a substantial contributor to the
> characteristic impedance (differential or single-ended) of the trace. I.E.,
> the capacitance between the 2 traces is not the only significant
> contributor. The only exception I can think of might be a case where the
> differential pair is EXTREMEMLY decoupled from the motherboard ground, in
> which case it won't make a difference whether you connect the probes to
> motherboard ground or not.
>
> As far as I know, having a "virtual ground" between the 2 traces doesn't
> imply that there is 0 current flow through the ground plane.
>
> As far as what probe to use to launch onto small geometries, I too have had
> the most success using semi-rigid coax as my probe.
>
> Jeff Loyer
> (253) 371-8093
>
>
> -----Original Message-----
> From: Ron Miller [mailto:[email protected]]
> Sent: Friday, October 20, 2000 10:55 AM
> To: 'Bob Lewandowski'; Ken Taylor
> Cc: [email protected]
> Subject: RE: [SI-LIST] : Re: Diff probes for tdr.
>
>
> Good comments Bob
>
> If you are measuring a differential line, though, you do not
> have to connect the ground. All you are really intrested in
> is the differential impedance. The impedance to ground is
> irrelevant, because you have a virtual ground half way between
> the two differential drive pins anyway.
>
> Ron Miller
>
>
>
> > -----Original Message-----
> > From: Bob Lewandowski
> > Sent: Thursday, October 19, 2000 7:04 PM
> > To: Ken Taylor
> > Cc: [email protected]
> > Subject: Re: [SI-LIST] : Re: Diff probes for tdr.
> >
> > I concur with all the semi-rigid coax comments. Most all of the
> commercial
> > probes I've seen generate large launch discontinuities (~20%), with the
> > exception of Picoprobe, and Cascade Microtech (both $$$ !).
> >
> > I've used .047" diameter coax, either solid jacket or the tin dipped braid
> type
> > (very flexible). Tensolite/QMI sell .047 cable assemblies of the braid
> type
> > with male or female SMAs, that they call Semi-Flex. Just buy a 1 ft.
> cable and
> > chop it in half, match the lengths for differential. With the small coax
> you
> > can solder the jacket to a board ground next to a trace, and with a very
> short
> > center conductor, keep the launch reflection down to around 5%.
> Semi-rigid coax
> > typically can be obtained with tight tolerance on the Z0, so the cable
> becomes a
> > good reference impedance before the launch. Be cautious about minimizing
> the
> > length, as the small stuff is pretty lossy and degrades rise time.
> >
> > ---Bob Lewandowski
> > Vixel Corp.
> >
> > Ken Taylor wrote:
> >
> > > John Fisher's solution below is a very good one that I have used
> > > extensively. Although a little clumsy mechanically (you will want to use
> a
> > > probe positioner, hold the probe at about 45 degrees to get the tips and
> the
> > > ground to contact, keep the tips and ground path VERY short like 2 mm or
> so)
> > > they give great results. One more thing, however: If the probe impedance>
> > > doesn't match your DUT impedance, you will get reflections etc. and you
> > > won't be able to see anything close in to the contact point. To solve
> that,
> > > match the impedances as closely as possible, keep the probe (semi rigid
> > > stuff) more than, say, 6" long, and then all the mismatch will be at the
> > > flexible cable/probe connection, and you can keep it out of the way of
> your
> > > measurements. These probes work well for 17 pS Tr.
> > > One last thing, these things were whipped up for customers by friendly
> Tek
> > > AEs, and weren't part numbered for sale. (How can you charge $5000 for
> these
> > > things? Can't, so they don't sell them!) The real Tek (and Agilent)
> probes
> > > looked nice, are definitely nicer mechanically, but can't hold a light
> to
> > > these "do it yourself" probes.
> > >
> > > Regards, Ken.
> > >
> > > Ken Taylor
> > > Polar Instruments, Portland, OR, USA.
> > > [email protected]
> > >
> > > John said
> > > <<We have built these using equal length sections of semi rigid coax
> with
> > > sma's at one end. The semi rigid copper outer shield is soldered
> together
> > > approx. every 3 ". Prepare the ends by careful cutting of the
> > > shield with an exacto knife, than solder the center conductors to
> > > the launch point vias or pads. Tektronix shipped some of these to
> > > us as accessories when we bought their IPA-510 a few years ago. I
> > > might be able to find a tek part number but someone like Micro-Coax
> could
> > > make some for you or find an off the shelf semi rigid assembly with
> sma's
> > > on both ends and then just cut it in half. Be carful not to bend it too
> > > much and kink it. These can also make nice 50 Ohm 10x passive
> > > probes with the addition of a series 450 resistor at the end.<br> >>
> > >
> > > ----- Original Message -----
> > > From: "si-list-digest" <[email protected]>
> > > To: <[email protected]>
> > > Sent: Thursday, October 19, 2000 5:00 PM
> > > Subject: si-list-digest V1 #286>
> > >
> > > >
> > > > si-list-digest Thursday, October 19 2000 Volume 01 :
> Number
> > > 286
> > > >
> > > >
> > > >
> > > > In this issue:
> > > >
> > > > 1.) [SI-LIST] : High Frequency Seminar
> > > > "chasgra" <[email protected]>
> > > >
> > > > 2.) [SI-LIST] : SI - Salary Survey
> > > > sainath nimmagadda <[email protected]>
> > > >
> > > > 3.) [SI-LIST] : Differential TDR probes
> > > > "zanella, fabrizio" <[email protected]>
> > > >
> > > > 4.) Re: [SI-LIST] : Differential TDR probes
> > > > "Ritesh Kapahi" <[email protected]>
> > > >
> > > > 5.) Re: [SI-LIST] : Differential TDR probes
> > > > [email protected]
> > > >
> > > > 6.) RE: [SI-LIST] : Differential TDR probes
> > > > "Daniel, Erik S." <[email protected]>
> > > >
> > > > 7.) Re: [SI-LIST] : Differential TDR probes
> > > > John Fisher <[email protected]>
> > > >
> > > >
> > > > ----------------------------------------------------------------------
> > > >
> > > > Date: Wed, 18 Oct 2000 18:30:58 -0700
> > > > From: "chasgra" <[email protected]>
> > > > Subject: [SI-LIST] : High Frequency Seminar
> > > >
> > > > This is a multi-part message in MIME format.
> > > >
> > > > - ------=_NextPart_000_000C_01C03931.8EE7A3A0
> > > > Content-Type: text/plain;
> > > > charset="iso-8859-1"
> > > > Content-Transfer-Encoding: quoted-printable
> > > >
> > > > Rocky Mountain Chapter EMC Society presents:
> > > >
> > > > High Frequency Measurements and Noise in Electronic Circuits
> > > > - - one day demonstration based seminar.
> > > >
> > > > An informative and entertaining multimedia seminar for digital and =
> > > > analog designers as well as test engineering and EMC personnel.=20
> > > >
> > > > by Douglas C. Smith=20
> > > >
> > > > Author of High Frequency Measurements and Noise in Electronic
> Circuits=20
> > > >
> > > > An Unusual Seminar - Sign up here.>
> > > >
> > > > > This seminar is unique. Demonstrations on real circuits are used to =
> > > > illustrate most of the concepts being taught unlike most seminars
> which =
> > > > are taught through the use of vu-graphs as the main medium. About 70%
> of =
> > > > class time is spent in demonstrations. Complicated math is avoided.
> This =
> > > > format makes the seminar more interesting to the students and helps
> them =
> > > > to achieve a deeper understanding of the material covered. Many
> students =
> > > > have said that this was the best technical seminar they ever
> attended!=20
> > > >
> > > >
> > > >
> > > > When: Dec 1 2000
> > > >
> > > > If you are interested then goto our weblink: =
> > > > http://www.ewh.ieee.org/r5/denver/rockymountainemc
> > > >
> > > > Look for the Dec 1 meeting link and sign up!!
> > > >
> > > > Charles Grasso
> > > > Vice Chair RMCEMCS
> > > >
> > > >
> > > > - ------=_NextPart_000_000C_01C03931.8EE7A3A0
> > > > Content-Type: text/html;
> > > > charset="iso-8859-1"
> > > > Content-Transfer-Encoding: quoted-printable
> > > >
> > > > <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
> > > > <HTML><HEAD>
> > > > <META content=3D"text/html; charset=3Dwindows-1252" =
> > > > http-equiv=3DContent-Type>
> > > > <META content=3D"MSHTML 5.00.2919.6307" name=3DGENERATOR></HEAD>
> > > > <BODY bgColor=3D#ffffff>
> > > > <DIV><FONT size=3D2>
> > > > <P align=3Dcenter><A name=3DTitle><FONT size=3D6>Rocky Mountain
> Chapter =
> > > > EMC=20
> > > > Society</FONT></A><FONT size=3D6> presents:</FONT></P>
> > > > <P align=3Dcenter><FONT color=3D#0000ff face=3DArial size=3D6><B>High
> =
> > > > Frequency=20
> > > > Measurements and Noise</B></FONT> <FONT color=3D#0000ff face=3DArial =
> > > > size=3D6><B>in=20
> > > > Electronic Circuits<BR></B></FONT><FONT color=3D#0000ff face=3DArial =
> > > > size=3D5><B>- one=20
> > > > day demonstration based seminar.</B></FONT></P>
> > > > <P align=3Dcenter><FONT size=3D5><I>An informative and
> </I></FONT><FONT=20
> > > > color=3D#ff0000 size=3D5><B><I><U>entertaining</U></I></B></FONT><FONT
> =
> > > > size=3D5><I>=20
> > > > multimedia seminar for digital and analog designers as well as test =
> > > > engineering=20
> > > > and EMC personnel.</I></FONT> </P>
> > > > <P align=3Dcenter><FONT face=3DArial size=3D4><B>by </B></FONT><A=20>
> > > >
> href=3D"http://www.ewh.ieee.org/r5/denver/rockymountainemc/1dayemc.htm#Ab=
> > > > out The Instructor"><FONT=20
> > > > face=3DArial size=3D4><B>Douglas C. Smith</B></FONT></A> </P>
> > > > <P align=3Dcenter><FONT size=3D4>Author of <I>High Frequency =
> > > > Measurements and Noise=20
> > > > in Electronic Circuits</I></FONT> </P>
> > > > <P align=3Dcenter><A=20
> > > >
> href=3D"http://www.ewh.ieee.org/r5/denver/rockymountainemc/seminarsignup.=
> > > > htm"><FONT=20
> > > > size=3D5><B><U>An Unusual Seminar - Sign up
> here.</U></B></FONT></A></P>
> > > > <P align=3Dleft>This seminar is unique. Demonstrations on real
> circuits =
> > > > are used=20
> > > > to illustrate most of the concepts being taught unlike most seminars =
> > > > which are=20
> > > > taught through the use of vu-graphs as the main medium. About 70% of =
> > > > class time=20
> > > > is spent in demonstrations. Complicated math is avoided. This format =
> > > > makes the=20
> > > > seminar more interesting to the students and helps them to achieve a =
> > > > deeper=20
> > > > understanding of the material covered. Many students have said that
> this =
> > > > was the=20
> > > > <I>best</I> technical seminar they ever attended! </P>
> > > > <P align=3Dleft> </P>
> > > > <P align=3Dleft>When: Dec 1 2000</P>
> > > > <P align=3Dleft>If you are interested then goto our weblink: <A=20
> > > >
> href=3D"http://www.ewh.ieee.org/r5/denver/rockymountainemc">http://www.ew=
> > > > h.ieee.org/r5/denver/rockymountainemc</A></P>
> > > > <P align=3Dleft>Look for the Dec 1 meeting link and sign up!!</P>>
> > > > <P align=3Dleft>Charles Grasso<BR>Vice Chair=20
> >> > > RMCEMCS</P></FONT></DIV></BODY></HTML>
> > > >
> > > > - ------=_NextPart_000_000C_01C03931.8EE7A3A0--
> > > >
> > > >
> > > >
> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > ****
> > > >
> > > > ------------------------------
> > > >
> > > > Date: Thu, 19 Oct 2000 11:44:46 -0800
> > > > From: sainath nimmagadda <[email protected]>
> > > > Subject: [SI-LIST] : SI - Salary Survey
> > > >
> > > > Hi SI folks:
> > > >
> > > > I understand that with growing complexity in multimedia technology, SI
> > > > positions are getting increasingly challenging (we see "PhD preferred"
> > > > in ads)and hopefully lucrative too. We often find salary surveys for
> > > > mainstream folks such as IT professionals. I am just curious if there
> is
> > > > some kind of salary survey for SI folks too. I am sure that helps us
> SI
> > > > folks have an idea where we stand in this dynamic market.
> > > >
> > > > Best,
> > > >
> > > > SN
> > > > _____________________________________________________________
> > > > Tired of limited space on Yahoo and Hotmail?
> > > > Free 100 Meg email account available at http://www.dacafe.com
> > > >
> > > >
> > > >
> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > ****
> > > >
> > > > ------------------------------
> > > >
> > > > Date: Thu, 19 Oct 2000 15:44:15 -0400
> > > > From: "zanella, fabrizio" <[email protected]>
> > > > Subject: [SI-LIST] : Differential TDR probes
> > > >
> > > > We're having problems getting a good high frequency launch when
> probing pc
> > > > boards and cable differential pairs when taking TDR measurements.Has
> > > anyone
> > > > found good differential TDR probes which allow you to measure very
> closely
> > > > spaced points on pc boards or cables?
> > > >
> > > > Thanks and regards,
> > > > Fabrizio Zanella
> > > > Hardware Engineering
> > > > EMC Corporation
> > > > [email protected]
> > > >
> > > >
> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to>
> > > > [email protected]. In the BODY of message put: UNSUB> SCRIBE
> > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > ****
> > > >
> > > > ------------------------------
> > > >
> > > > Date: Thu, 19 Oct 2000 14:12:22 -0700
> > > > From: "Ritesh Kapahi" <[email protected]>
> > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > >
> > > > Agilent has got some micro probe which is an accessory for their high
> > > > bandwidth scope 86100 and differential TDR module 54754A . It usually
> has
> > > a
> > > > long lead times (3-4 months)
> > > > Bye
> > > > Kaps
> > > >
> > > > - ----- Original Message -----
> > > > From: zanella, fabrizio <[email protected]>
> > > > To: SI List (E-mail) <[email protected]>
> > > > Sent: Thursday, October 19, 2000 12:44 PM
> > > > Subject: [SI-LIST] : Differential TDR probes
> > > >
> > > >
> > > > > We're having problems getting a good high frequency launch when
> probing
> > > pc
> > > > > boards and cable differential pairs when taking TDR measurements.Has
> > > > anyone
> > > > > found good differential TDR probes which allow you to measure very
> > > closely
> > > > > spaced points on pc boards or cables?
> > > > >
> > > > > Thanks and regards,
> > > > > Fabrizio Zanella
> > > > > Hardware Engineering
> > > > > EMC Corporation
> > > > > [email protected]
> > > > >
> > > > >
> > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to>
> > > > > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > ****
> > > > >
> > > > >
> > > >
> > > >
> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > ****
> > > >
> > > > ------------------------------
> > > >
> > > > Date: Thu, 19 Oct 2000 16:39:38 -0500
> > > > From: [email protected]
> > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > >
> > > > Kaps,
> > > >
> > > > Have you comfirmed that the TDR Module 54754A works with their new
> 86100A
> > > main
> > > > frame?
> > > > They (their sales guys) tell me that it will not be ready until Dec
> 00.
> > > >
> > > > Thanks,
> > > > - -- Sal
> > > >
> > > >
> > > >
> > > >
> > > > "Ritesh Kapahi" <[email protected]> on 10/19/2000 04:12:22 PM
> > > >
> > > > Please respond to "Ritesh Kapahi" <[email protected]>
> > > >
> > > > Sent by: "Ritesh Kapahi" <[email protected]>
> > > >
> > > >
> > > > To: "zanella, fabrizio" <[email protected]>, "SI List
> > > > cc: (Salvador Aguinaga/MW/US/3Com)
> > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > >
> > > >
> > > >
> > > > Agilent has got some micro probe which is an accessory for their high
> > > > bandwidth scope 86100 and differential TDR module 54754A . It usually
> has
> > > a
> > > > long lead times (3-4 months)
> > > > Bye
> > > > Kaps
> > > >
> > > > - ----- Original Message -----
> > > > From: zanella, fabrizio <[email protected]>
> > > > To: SI List (E-mail) <[email protected]>
> > > > Sent: Thursday, October 19, 2000 12:44 PM
> > > > Subject: [SI-LIST] : Differential TDR probes
> > > >
> > > >
> > > > > We're having problems getting a good high frequency launch when
> probing
> > > pc
> > > > > boards and cable differential pairs when taking TDR measurements.Has
> > > > anyone
> > > > > found good differential TDR probes which allow you to measure very
> > > closely
> > > > > spaced points on pc boards or cables?
> > > > >
> > > > > Thanks and regards,
> > > > > Fabrizio Zanella
> > > > > Hardware Engineering
> > > > > EMC Corporation
> > > > > [email protected]
> > > > >
> > > > >
> > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > si-list archives are accessible at > http://www.qsl.net/wb6tpu
> > > > > ****
> > > > >
> > > > >
> > > >
> > > >
> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > ****
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > ****
> > > >
> > > > ------------------------------
> > > >
> > > > Date: Thu, 19 Oct 2000 17:26:16 -0500
> > > > From: "Daniel, Erik S." <[email protected]>
> > > > Subject: RE: [SI-LIST] : Differential TDR probes
> > > >
> > > > Fabrizio-
> > > >
> > > > A couple things we have used with some success for diff TDR on PC
> boards
> > > and
> > > > chip packages:
> > > >
> > > > 1. GGB Picoprobe Model 10
> > > > - -------------------------->
> > > > These are micro-coax probes with needle-like tips connected at the
> end.
> > > > They are pretty cheap, and there are a wide variety of options
> (different
> > > > needle tip lengths, widths, materials, ...). We have used two
> > > ground-signal
> > > > style probes soldered together to form a GSSG style differential
> probe.
> > > The
> > > > needles are flexible and can be bent to accommodate different board
> > > > geometries (although bending the needles too much definitely degrades
> the
> > > > launch). There are some technical drawbacks to these, but they have
> come
> > > in
> > > > handy for troubleshooting.
> > > >
> > > > 2. GGB Picoprobe Model 40A Dual probes
> > > > - ---------------------------------------
> > > > These are very good microwave probes (with an advertised 40 GHz
> bandwidth)
> > > > that you can buy in GSSG or GSGSG styles in a variety of pitches.
> They
> > > are
> > > > fairly expensive, the lead times are long for custom orders, and I
> would
> > > not
> > > > recommend trying to bend these(!) to accommodate different geometries,
> but
> > > > they are electrically very good.
> > > >
> > > > There are a number of other similar microwave probes we have used in
> > > various
> > > > special cases, but I think I have used these two options the most.
> > > >
> > > > - Erik
> > > >
> > > > ==================================================================
> > > > Erik Daniel, Ph.D. Mayo Foundation
> > > > Voice: (507) 284-1634 Guggenheim 1011B
> > > > Fax: (507) 284-9171 200 First Street SW
> > > > E-mail: [email protected] Rochester, MN 55905
> > > > ==================================================================
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: zanella, fabrizio [mailto:[email protected]]
> > > > > Sent: Thursday, October 19, 2000 2:44 PM
> > > > > To: SI List (E-mail)
> > > > > Subject: [SI-LIST] : Differential TDR probes
> > > > >
> > > > >
> > > > > We're having problems getting a good high frequency launch
> > > > > when probing pc
> > > > > boards and cable differential pairs when taking TDR
> > > > > measurements.Has anyone
> > > > > found good differential TDR probes which allow you to measure
> > > > > very closely
> > > > > spaced points on pc boards or cables?
> > > > >
> > > > > Thanks and regards,
> > > > > Fabrizio Zanella
> > > > > Hardware Engineering
> > > > > EMC Corporation
> > > > > [email protected]
> > > > >
> > > > >
> > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > ****
> > > > >
> > > >
> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > [email protected]. In the BODY of message put: UNSUBSCRIBE>
> > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > ****
> > > >
> > > > ------------------------------
> > > >
> > > > Date: Thu, 19 Oct 2000 15:38:44 -0700
> > > > From: John Fisher <[email protected]>
> > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > >
> > > > <html>
> > > > <font size=3>Fabrizio,<br>
> > > > <br>
> > > > We have built these using equal length sections of semi rigid coax
> with
> > > > sma's at one end. The semi rigid copper outer shield is soldered
> together
> > > > approx. every 3 ". Prepare the ends by careful cutting of
> the
> > > > shield with an exacto knife, than solder the center conductors
> to
> > > > the launch point vias or pads. Tektronix shipped some of these
> to
> > > > us as accessories when we bought their IPA-510 a few years ago. >
> I
> > > > might b> e able to find a tek part number but someone like Micro-Coax
> could
> > > > make some for you or find an off the shelf semi rigid assembly with
> sma's
> > > > on both ends and then just cut it in half. Be carful not to bend it
> too
> > > > much and kink it. These can also make nice 50 Ohm 10x passive
> > > > probes with the addition of a series 450 resistor at the end.<br>
> > > > <br>
> > > > Regards<br>
> > > > <br>
> > > > John<br>
> > > > <br>
> > > > At 03:44 PM 10/19/00 -0400, you wrote:<br>
> > > > <blockquote type=cite cite>We're having problems getting a good high
> > > > frequency launch when probing pc<br>
> > > > boards and cable differential pairs when taking TDR measurements.Has
> > > > anyone<br>
> > > > found good differential TDR probes which allow you to measure very
> > > > closely<br>
> > > > spaced points on pc boards or cables?<br>
> > > > <br>
> > > > Thanks and regards,<br>
> > > > Fabrizio Zanella<br>
> > > > Hardware Engineering<br>
> > > > EMC Corporation<br>
> > > > [email protected]<br>
> > > > <br>
> > > > <br>
> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to<br>
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> > > > ****</font></blockquote><br>
> > > >
> > >
> <div>*********************************************************************</
> > > div>
> > > > <div>John M. Fisher -- Cisco Systems -- [email protected]</div>
> > > > <div> 170 W. Tasman Dr., Bldg G, San
> Jose
> > > > CA 95134-1706</div>
> > > >
> > >
> <div><x-tab> </x-tab> &n
> > > bsp;
> > > > __
> > > >
> > >
> _ &nb
> > > sp;
> > > > _</div>
> > > > <div> ________/// \_/
> > > > \________/ \ ____</div>
> > > >
> > >
> <div><x-tab> </x-tab><x-tab>&
> > >
> nbsp; </x-tab><x-tab> &n
> > >
> bsp; </x-tab><x-tab> &nb
> > > sp; </x-tab>
> > > > \/</div>
> > > > <div>Manager Signal Integrity, Enterprise Line of Business</div>
> > > > <div>408-527-9186, Page 408-308-5501, Fax 408-526-5504,
> > > > N6PFN</div>
> > > > *********************************************************************
> > > > </html>
> > > >
> > > >
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