[SI-LIST] Re: Definition of "crosstalk loss" ??
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: wolfgang.maichen@xxxxxxxxxxxx
- Date: Wed, 05 Dec 2007 13:33:18 -0500
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.
Sdd21 = insertion loss of victim
Sdd43 = insertion loss of aggressor
Sdd13 = near end crosstalk NEXT
Sdd21 = far end crosstalk FEXT = "crosstalk loss"
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® 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 text
> 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 the
> 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 to
> 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 going
> 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 is
> 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:
> //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:
> //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 technical documents are available at:
> http://www.si-list.net
>
> 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 technical documents are available at:
http://www.si-list.net
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
Other related posts:
