Re: [SI-LIST] : Re: Diff probes for tdr.

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From: Dima Smolyansky ([email protected])
Date: Mon Oct 23 2000 - 20:55:27 PDT

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In reply to: Ron Miller: "RE: [SI-LIST] : Re: Diff probes for tdr."
Next in thread: David Instone: "Re: [SI-LIST] : Re: Diff probes for tdr."

The key thing, I think, is that Jeff is looking for differential and common
mode characterization of his signals. For common mode characterization, a
connection to the ground plane is required.

If you don't make a connection to the ground plane, you assume that your
signals are perfectly balanced and completely disregard the common mode.

Thanks,

===================
Dima Smolyansky
TDA Systems, Inc.
11140 SW Barbur Blvd., Suite 100
Portland, OR 97219
(503) 246-2272
(503) 246-2282 (fax)
(503) 804-7171 (mobile)
http://www.tdasystems.com
The Interconnect Modeling Company(TM)

----- Original Message -----
From: "Ron Miller" <[email protected]>
To: "'Loyer, Jeff W'" <[email protected]>; "Ron Miller"
<[email protected]>; "'Bob Lewandowski'" <[email protected]>; "Ken
Taylor" <[email protected]>
Cc: <[email protected]>
Sent: Monday, October 23, 2000 11:24 AM
Subject: RE: [SI-LIST] : Re: Diff probes for tdr.

> 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. >>
> > > >
> > > > ----- 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>
> > > > > <A name=3DTitle>Rocky Mountain
> > Chapter =
> > > > > EMC=20
> > > > > Society</A> presents:
> > > > > High
> > =
> > > > > Frequency=20
> > > > > Measurements and Noise > > > > size=3D6>in=20
> > > > > Electronic Circuits > > > > size=3D5>- one=20
> > > > > day demonstration based seminar.
> > > > > An informative and
> > <FONT=20
> > > > > color=3D#ff0000
size=3D5>entertaining > =
> > > > > size=3D5>=20
> > > > > multimedia seminar for digital and analog designers as well as
test =
> > > > > engineering=20
> > > > > and EMC personnel. 
> > > > > by
<A=20>
> > > > >
> >
href=3D"http://www.ewh.ieee.org/r5/denver/rockymountainemc/1dayemc.htm#Ab=
> > > > > out The Instructor"><FONT=20
> > > > > face=3DArial size=3D4>Douglas C. Smith</A> 
> > > > > Author of High Frequency =
> > > > > Measurements and Noise=20
> > > > > in Electronic Circuits 
> > > > > <A=20
> > > > >
> >
href=3D"http://www.ewh.ieee.org/r5/denver/rockymountainemc/seminarsignup.=
> > > > > htm"><FONT=20
> > > > > size=3D5>An Unusual Seminar - Sign up
> > here.</A>
> > > > > 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
> > > > > best technical seminar they ever attended! 
> > > > >  
> > > > > When: Dec 1 2000
> > > > > 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>
> > > > > Look for the Dec 1 meeting link and sign up!!>
> > > > > Charles Grasso Vice Chair=20
> > >> > > RMCEMCS</DIV></BODY></HTML>
> > > > >
> > > > > - ------=_NextPart_000_000C_01C03931.8EE7A3A0--
> > > > >
> > > > >
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> > > > > ****
> > > > >
> > > > > ------------------------------
> > > > >
> > > > > 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
> > > > >
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> > > > > ****
> > > > >
> > > > > ------------------------------
> > > > >
> > > > > 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:
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> > > > > 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
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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:
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> > > > > ****
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
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> > > > >
> > > > > ------------------------------
> > > > >
> > > > > 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
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> > > > > > [email protected]. In the BODY of message put:
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> > > > > > ****
> > > > > >
> > > > >
> > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > [email protected]. In the BODY of message put:
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> > > > > ****
> > > > >
> > > > > ------------------------------
> > > > >
> > > > > Date: Thu, 19 Oct 2000 15:38:44 -0700
> > > > > From: John Fisher <[email protected]>
> > > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > > >
> > > > > <html>
> > > > > Fabrizio, 
> > > > > 
> > > > > 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. 
> > > > > 
> > > > > Regards 
> > > > > 
> > > > > John 
> > > > > 
> > > > > At 03:44 PM 10/19/00 -0400, you wrote: 
> > > > > <blockquote type=cite cite>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
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> > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put
HELP. 
> > > > > si-list archives are accessible at 
> > > > > <a href="http://www.qsl.net/wb6tpu"
> > > > eudora="autourl">http://www.qsl.net/wb6tpu> 
> > > > > ****</blockquote> 
> > > > >
> > > >
> >
<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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> > > > >
> > > > > ------------------------------>
> > > > >
> > > > > End of si-list-digest V1 #286
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