[time-nuts] inexpensive fiber optic distribution

[Warren Kumari]

On Thu, Mar 21, 2019 at 7:05 AM Anders Wallin <anders.e.e.wallin at gmail.com>
wrote:

> We've tinkered with SFP-to-SMA adapter boards like this:
> https://github.com/aewallin/SFP2SMA_2018.03
> http://www.anderswallin.net/2018/04/500-mhz-sfp-board-v4/
>

And if you want a "ready made" solution instead of making the board
yourself, etc there is
http://shop.sysmocom.de/t/development-boards/sfp


I have some on order to play with, but am traveling, and so cannot play
with them yet.

W


> although designed for 1 Gbit (1.25 GHz, or 800 ps 'bits') they work down to
> 10 MHz (and 5 MHz IIRC).
> With a decent interface-board and a short bit of fiber the ADEV noise floor
> is very close to what is measurable with a 3120A (aka TimePod).
> IIRC a rough rule-of-thumb is that the fiber can add around 1e-16/meter. So
> add 1km of fibre and you can expect fluctuations at 1e-13 level -
> roughly...
>
> AW
>
> On Thu, Mar 21, 2019 at 6:06 AM jimlux <jimlux at earthlink.net> wrote:
>
> > While researching this for a radio telescope, I found amazingly
> > inexpensive (<$10) fiber optic transceivers for 1Gbps sorts of rates..
> >
> > They take a standard singlemode duplex fiber and have a pinout suitable
> > for plugging into a Cisco, etc. switch. Apparently, there's some
> > internal programming which sets the hardware for the kind of switch,
> > rates, etc..  fs.com has a generic ASIC inside the adapter which can be
> > reprogrammed for whatever formatting, compatibility etc is needed. The
> > astronomers were saying that at Berkeley, they bought a box for a few k
> > which allows them to reconfigure the transceivers.
> >
> >
> > Something like this:
> > https://www.fs.com/products/12622.html
> >
> > Data sheet here:
> https://img-en.fs.com/file/datasheet/sfp1g-lx-31-10km.pdf
> >
> > and a 10 meter patch cable is $5
> > https://www.fs.com/products/40203.html
> >
> > This is sort of "old news" in the networking world (the SFP form factor
> > was defined in 2001)
> >
> >
> > It seems like you could probably figure out how to interface to these
> > things and use them to distribute timing signals.
> >
> > I'll be talking to the radio astronomers tomorrow again, and I'll see
> > what I can find out about interfaces. I suspect they do NOT use them for
> > conventional networking - they're all about running lots of bits from
> > antennas into large multichannel correlators/beamformers.
> >
> > They're buying these things by the dozen.
> >
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-- 
I don't think the execution is relevant when it was obviously a bad idea in
the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair of
pants.
   ---maf