[time-nuts] inexpensive fiber optic distribution

[Gerhard Hoffmann]

Am 21.03.19 um 07:27 schrieb Hal Murray:
> jimlux at earthlink.net said:
>> It seems like you could probably figure out how to interface to these  things
>> and use them to distribute timing signals.

The document is the "SFP MSA".  I still have the XFP version somewhere here.

> I don't know how well they will work for something like a PPS.  Somebody
> should try it.  The signal pattern is mostly trying to be friendly to the PLL
> that does clock recovery and/or the AGC that sets up the switching level.
>
> If I wanted to send a PPS, I'd use something simple like Manchester encoding.
> That assumes you can line your transmit clock up with the PPS.  It won't work
> if you just want a link-extender for a PPS.


Manchester should work. Simply trying to transmit a differential CML 
level 1pps won't do.

The signals are ac-coupled typically 100nF/50 Ohm right at the module 
border.

I was one of the ~5 people who did the electronics of the 10 GBPS XFP 
modules

at Infineon Fiber Optics (RIP, sold) and someone decreased the coupling

capacitors to 10n for a very minor advantage. It's 10 GBPS, pure RF 
after all.

No. That gave us 1 bit error per day (complete show stopper) and a month 
of delay.


I'm puzzled that it works so far off-frequency with these SFPs. In our 
10 GBPS XFPs

it would definitely not work. The eye opener at the input to the 
transmitter would

go nuts, and the receiver clock recovery would not work.


BTW our modules for Cisco had special contents in some registers to make 
sure

that nobody could use alien modules. There must have happened some

social engineering if I read the post above :-)


regards,

Gerhard