[time-nuts] inexpensive fiber optic distribution

[Anders Wallin]

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/

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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