[time-nuts] inexpensive fiber optic distribution

[jimlux]

On 3/20/19 11:42 PM, Warren Kumari wrote:
> 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
> 


This is very interesting stuff...
There have been times I was thinking "what I really need here is a 
optical link for the 10 or 100 MHz".. But "hundreds of dollars" was a 
bit steep.  This is starting to get more reasonable (still, about $200 
for a link, by the time you buy/assemble adapter boards, the $7 modules, 
and some fiber).

As far as the reprogramming goes (another comment on the list) - I 
understand that is to make the unit have some particular flavor 
SFP-wise.  If you were plugging them into a Cisco switch and all you had 
was ones configured for Juniper switches, then you'd want to do that. At 
the multikilobuck level to do this, you'd need a LOT of them to make it 
worthwhile.  The folks building radio telescope arrays with hundreds of 
cables probably fit in that use case.  A devoted time-nut using it to 
distribute their reference around the house or lab, probably not.




> 
>> 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
>>