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RE: A couple of questions on clause 52





> -----Original Message-----
> From: Jonathan Thatcher 
> [mailto:Jonathan.Thatcher@worldwidepackets.com]
> Sent: 17 April 2001 02:30
> To: serialpmd
> Subject: A couple of questions on clause 52
> 
> Would someone please remind me:
> 
> 1. Why is it that in the OMA tables that we spec the dBm 
> range in OMA/2
> instead of just OMA? We specify the Rx in OMA (dBm). Are we 
> just testing to
> see if the user knows to add 3dB when working on the link 
> budgets?  :-)

It's the difference between preferring to measure the "peak" value of a
time-varying ("AC")voltage/current/lightbeam or the "peak-to-peak".  We
inherit the traditional measure of signal strength,

	dBm(average) = dBm(peak)+ dB(extinction ratio penalty)

We also inherit OMA, defined on a peak-to-peak basis.  So we are stuck with
an untidy situation.  My preference is to use dB(OMA/2), daft as it looks,
because that provides better compatibility with traditional specifications
and actual power meters.  I'd really like to redefine OMA, but I guess it's
too late for that.

> 2. What did we mean in Table 52-21 that the Minimum 
> dispersion in ps/nm for
> ER/EW be the worst of i) 0.93... and ii) 0?
> If Lamda is within the specifications (1530 to 1565 nm) 
> required for ER/EW,
> when would 0 (zero) be the worst case?

Facile answer:
We are just declaring a range of dispersions, from most positive to most
negative.  We aren't taking a position on which end of the range is worst.
Perhaps you could suggest better wording in a comment.

Techie answer:
Negative dispersion penalties are possible, so there could be doubt about
which end is worst.

Hope I answered your questions,

Piers

> 
> jonathan
>