|
[si-list]
||
[Date Prev]
[12-2007 Date Index]
[Date Next]
||
[Thread Prev]
[12-2007 Thread Index]
[Thread Next]
[SI-LIST] Re: Definition of "crosstalk loss" ??
- From: "Rost, Michael" <Michael.Rost@xxxxxxxxx>
- To: <scott@xxxxxxxxxxxxx>, <wolfgang.maichen@xxxxxxxxxxxx>
- Date: Wed, 5 Dec 2007 13:46:43 -0600
Straight from the network analyzer, the magnitudes of Sdd13 and Sdd23 as ex=
pressed in dB are going to be negative numbers. I think the IEEE tacks on =
the word "loss" to crosstalk to simply indicate that they have written thei=
r specification in terms of the absolute magnitude of the measured crosstal=
k which ends up being a positive number when expressed in dB.
Look at the formulas and graphs for crosstalk in any of the 802.3 specifica=
tions (well, at least those that I've reviewed) and you'll notice that the =
specifications are all greater than 0 dB over the applicable frequency rang=
e. You might not see this at first since, if a graph is included, they see=
m to generally flip the y-axis so 0 dB is at the top (look at 802.3ak). Th=
e same thing is done for insertion loss and return loss in these specificat=
ions: absolute magnitude is specified so all the numbers are greater than z=
ero.
Regards, Mike
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On=
Behalf Of Scott McMorrow
Sent: Wednesday, December 05, 2007 12:33 PM
To: wolfgang.maichen@xxxxxxxxxxxx
Cc: hreidmarkailen@xxxxxxxxx; si-list; si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Definition of "crosstalk loss" ??
Actually, I believe all measurements are made w.r.t. the victim.
Crosstalk loss is the energy that the sum total of the aggressors impart =
on the victim. In a 4-line system with 4 differential ports.
----- edited -----
Sdd21 =3D insertion loss of victim
Sdd43 =3D insertion loss of aggressor
Sdd13 =3D near end crosstalk NEXT
Sdd23 =3D far end crosstalk FEXT =3D "crosstalk loss"
----- edited -----
When the moon and stars line up and all aggressors fire at a point and =
phase where they destructively interfere with the victim at the =
receiver, then you have an apparent loss, or "crosstalk loss". =
Interestingly enough, if the aggressors constructively interfere with =
the victim, then you get an apparent gain, or "crosstalk gain". They =
use a power sum for multiple aggressors, based on the assumption that =
not all aggressors will be at the worst case phase alignment with the =
victim at any time. Personally, I'd much rather use a linear sum, just =
to be sure.
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed=AE is the registered service mark of
Teraspeed Consulting Group LLC
wolfgang.maichen@xxxxxxxxxxxx wrote:
> I have to admit I haven't heard that term myself before. But from the tex=
t =
> it looks like they mean the signal loss in the agressor - keep in mind =
> that the crosstalk signal (energy) in the victim has to come from =
> somewhere, so if there is to be a crosstalk signal on the victim, then th=
e =
> agressor must experience signal loss. Loss in aggressor signal voltage is=
=
> often not as easily visible, for two reasons. Since power is proportional=
=
> to the square of the voltage, a 1% energy loss due to crosstalk amounts t=
o =
> only an approx. 0.5% reduction in aggressor signal. In addition, it's =
> easier to observe the crosstalk on the victim going from e.g. 0 to 10mV -=
=
> a large relative change - than it is to observe the aggressor signal goin=
g =
> from 1000mV to 995mV - a very small relative change -, which can hide the=
=
> effect in practical scope measurements and lead to the false belief that =
> crosstalk only affects the victim but not the aggressor.
> Wolfgang
>
>
>
>
>
>
> agathon <hreidmarkailen@xxxxxxxxx> =
> Sent by: si-list-bounce@xxxxxxxxxxxxx
> 12/04/2007 05:01 PM
> Please respond to
> hreidmarkailen@xxxxxxxxx
>
>
> To
> si-list <si-list@xxxxxxxxxxxxx>
> cc
>
> Subject
> [SI-LIST] Definition of "crosstalk loss" ??
>
>
>
>
>
>
> Hello all,
> I'm trying to make clearer the following statement from 802.3ap:
>
> "...FEXTn is the crosstalk loss, in dB, of aggressor n."
>
> What the heck is "crosstalk loss"????
>
>
> The full paragraph is:
>
> 69B.4.6.2 Power sum differential far-end crosstalk (PSFEXT)
> The differential far-end crosstalk at TP4 is calculated as the power sum =
> of
> the individual FEXT aggressors
> (PSFEXT). PSFEXT is computed as shown in Equation (69B?16), where FEXTn i=
s
> the crosstalk loss, in dB,
> of aggressor n. Note that for the case of a single aggressor, PSFEXT will=
=
> be
> the crosstalk loss for that single
> aggressor.
>
>
> Thanks,
> Agathon
>
> ------------
>
> ------------------------------------------------------------------
> 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:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at: =
> http://www.freelists.org/archives/si-lis=
t
> 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:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at: =
> http://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:
http://www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at: =
http://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
=
CONFIDENTIALITY NOTICE: This message (including any attachments) may contai=
n Molex confidential information, protected by law. If this message is conf=
idential, forwarding it to individuals, other than those with a need to kno=
w, without the permission of the sender, is prohibited.
This message is also intended for a specific individual. If you are not the=
intended recipient, you should delete this message and are hereby notified=
that any disclosure, copying, or distribution of this message or taking of=
any action based upon it, is strictly prohibited. =
Chinese Japanese
www.molex.com/confidentiality.html
------------------------------------------------------------------
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:
http://www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
http://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
|
|
