[SI-LIST] Re: Definition of "crosstalk loss" ??
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: scott@xxxxxxxxxxxxx
- Date: Wed, 05 Dec 2007 14:04:45 -0500
Oops
that should have been:
Sdd21 = insertion loss of victim
Sdd43 = insertion loss of aggressor
Sdd13 = near end crosstalk NEXT
Sdd23 = far end crosstalk FEXT = "crosstalk loss"
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
Scott McMorrow wrote:
> 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
>>
>> ------------
>>
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