[time-nuts] SE880 GPSDO

Michael Wouters michaeljwouters at gmail.com
Fri Apr 29 02:42:13 UTC 2016


According to this,

http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449

there are many practical challenges  with a one way free-space optical link.

They were, however, aiming for much higher stability than is needed here.

There are a lot of ideas being tossed around here. It would probably
help to focus the discussion a bit if we knew:
(1) The budget (presumably small)
(2) Site constraints - is there line of sight, is it really impossible
to run a fibre (I know trenching costs are high but a fibre strung
along a fence with some UV protection might be acceptable in this
application)
(3) What expertise there is that can be drawn upon

Cheers
Michael


On Fri, Apr 29, 2016 at 11:11 AM, Bruce Griffiths
<bruce.griffiths at xtra.co.nz> wrote:
> One advantage of a free space optical link for this application, is that most of the factors that produce severe attenuation of the optical signal also preclude observation of the stellar sources as well. Thus the link only needs to work well under near ideal conditions.Increasing the aperture of the transmit and receive optics reduces the required transmitter power and the associated safety hazards of the transmitted optical beam.
> Bruce
>
>
>     On Friday, 29 April 2016 1:02 PM, Bruce Griffiths <bruce.griffiths at xtra..co.nz> wrote:
>
>
>  If you add a small beam expander, then there should be few safety issues.In this case a laser beam power of a few (1??) mW may suffice.Similar collection optics at the receiver will also be required. One can use small telescopes for this purpose. I've used an eyepiece with a 12" (305mm) dobsonian to produce a 300mm diameter beam from a green laser pointer. You shouldn't need to go quite that far though.
> Bruce
>
>
>     On Friday, 29 April 2016 12:01 PM, Attila Kinali <attila at kinali.ch> wrote:
>
>
>  On Thu, 28 Apr 2016 23:22:24 +0200
> Attila Kinali <attila at kinali.ch> wrote:
>
>> > Thanks Attila, I know how to build a transmitter and a receiver, and now
>> > is more clear the system you designed. But as I will propose this system
>> > to an astro club, and in this astro club there's the possibility that
>> > not all would have a radio license, I need something "free-to-play", if
>> > it concern.
>>
>> Ok.. that's quite some constraint. This rules out any kind of transmission.
>
>
> Here another crazy idea:
>
> If you can ensure line of sight between stations, you can use a
> laser link between them. Modulate the laser with an RF signal in the
> 10-100MHz range. Use this on the receiver side to lock the OCXO.
> Proceed as before...
>
> This approach should be fairly simple to build, but needs some care
> to ensure that you are not endangering anyone with the laser beam.
> Other than that, you don't need a license for running such a system.
> There have been hobbyist laser communication links around for a couple
> of years, though i would advise to check the designs carfully as some
> of them have EMI and other problems that the original designers and users
> didn't care about.
>
>
>             Attila Kinali
>
>
> --
> Reading can seriously damage your ignorance.
>         -- unknown
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