Re: Oops

On Thu, 23 Feb 2012 21:53:22 -0500, Phil Hobbs
<(E-Mail Removed)> wrote:

>Robert Baer wrote:
>>
>> John Larkin wrote:
>> > On Wed, 22 Feb 2012 23:34:04 -0800, Robert Baer
>> > <(E-Mail Removed)> wrote:
>> >
>> >> Phil Hobbs wrote:
>> >>> John Walliker wrote:
>> >>>>
>> >>>> http://news.sciencemag.org/sciencein...8O-G8w.twitter
>> >>>>
>> >>>> It appears that the faster-than-light neutrino results, announced last
>> >>>> September by the OPERA collaboration in Italy, was due to a mistake
>> >>>> after all. A bad connection between a GPS unit and a computer may be
>> >>>> to blame.
>> >>>> ...
>> >>>> According to sources familiar with the experiment, the 60 nanoseconds
>> >>>> discrepancy appears to come from a bad connection between a fiber
>> >>>> optic cable that connects to the GPS receiver used to correct the
>> >>>> timing of the neutrinos' flight and an electronic card in a computer.
>> >>>> After tightening the connection and then measuring the time it takes
>> >>>> data to travel the length of the fiber, researchers found that the
>> >>>> data arrive 60 nanoseconds earlier than assumed.
>> >>>>
>> >>>> John
>> >>>
>> >>> That isn't too plausible unless they have really, really slow edges on
>> >>> that light pulse. I sort of suspect that they loosened a connector,
>> >>> removed 40 feet of fibre, and then tightened it again.
>> >>>
>> >>> Cheers
>> >>>
>> >>> Phil Hobbs
>> >>>
>> >>>
>> >> Light fibers are THAT slow? Then why not use less costly coax?
>> >
>> > About 2/3 c or something like that. About the same as coax.
>> >
>> > We use fiber because of the horrible pulse transmission of coax over
>> > tens of meters... rise times go to hell, and ground loops make things
>> > worse. You can shoot a 10 ns pulse over a kilometer of multimode fiber
>> > and it hardly changes. You can get 10 ps RMS edge jitter with cheap
>> > parts. Ditto a hundred km of singlemode.
>> >
>> > Multimode fiber is cheaper than good coax anyhow.
>> >
>> >
>> Hmm..as i remember, coax i used ran in the 80-90% C, a lot faster
>> than 60-70% cited for fiber.
>> Signal loss and edge loss over a long line is another story, natch.
>
>Foam dielectric coax can get up there, but it has a lot of drawbacks,
>e.g. when you bend it, the centre conductor tends to cut through the
>foam and cause all sorts of nasty impedance discontinuities, and in
>really bad cases, may even short to the shield.

The GoreTex "high-speed" coax we used in the '80s was pretty decent stuff,
albeit expensive as hell.