Re: [casper] fiber capacity

[Dan Werthimer]

Hi Jouko,

You can use fiber optic cables on the iBob, Roach and Bee2 boards. 

There are several vendors that make CX4 optical fiber cables;  these 
cables house copper to optical transceivers
in the connector body.  Matt Dexter has tested several vendors - we use 
optical CX4 cables at BWRC
and the Allen Telescope Array.   They cost more than copper cables (eg:  
~$300 from Zarlink),
but they can go long distances.

Best Wishes,

Dan

Hi,

OK, the dynamic range might be much better now, I remember something 
like 13 dB but it was year 1985 and first-generation 10 Mbps Ethernet.
The 45 dB sounds a bit weird, physics have stayed the same. Possibly 
some tricks in signal levels?

So there is still the standard question we ask all the students. "Why 
do you want to do that". The ones that have good answers get the best 
grades. :-)

IMHO, getting a good timing standard to the antenna and sampling as 
early as possible would be the easiest and best solution. I may be 
mistaken, I have been mistaken many times. No hard feelings if you 
prove me to be wrong.

Anyway, if cable conduit is available then lots of fibers are 
recommended. Usually the cable body costs about the same as fibers but 
96 fibers could be a mess to terminate. Unfortunately iBobs or roach 
boards do not have cradles for fiber optic transceivers, designing 
them in would have been real easy.

Cheers,
Jouko

"Life is pretty simple: You do some stuff. Most fails. Some works. You do
more of what works. If it works big, others quickly copy it. Then you do
something else. The trick is to do something else."


On Fri, 18 Dec 2009, Michael Inggs wrote:

Hi
Roufurd Julie's M.Sc. dissertation should come out early in January 2010
(yes, Roufurd, just next year...) and he has a lot of practical 
measurements
of gain changes with ambient, phase changes, changes due to the antenna
cable wraps, and so on. Dynamic range, now specified at the 1%GCP, is 
around
45dB, with the Foxcom links Justin mentioned.

Regards

Mike

2009/12/18 Jouko Ritakari <j...@kurp.hut.fi>
      Hi all,

      In the old days the biggest problem was the very limited dynamic
      range of fiber optic receivers. If you are thinking of using
      analog links you shoud check if this is still true and if it
      isn't, what tricks have been used to circumvent it.

      Otherwise all the different standards are a big mess, but if you
      know basic optics almost anything can be done. For example the
      operators routinely connect multimode and singlemode equipment
      by using inexpensive attenuators. Our 10 Gbps link uses dwdm in
      one end and inexpensive 10Gbase-ZR on the other, never had a
      problem.

      Using optics for high-speed digital links is surprisingly easy,
      I guess analog links are easy too if the signal strength is
      constant which is true for radio links, not true for radio
      astronomy.

      Please correct me if you think otherwise.

      Cheers,
      Jouko

      "Life is pretty simple: You do some stuff. Most fails. Some
      works. You do
      more of what works. If it works big, others quickly copy it.
      Then you do
      something else. The trick is to do something else."



On Fri, 18 Dec 2009, Justin Jonas wrote:

      Alan reminded me I should have given the link to the
      supplier:

      http://www.foxcom.com/index.aspx?id=2510

      J



      On 18 Dec 2009, at 12:53 AM, Tom Kuiper wrote:

            John Ford wrote:
                  We've decided (Maybe prematurely?)
                  that wide-band analog links are
                  not the
                  way to go, for single-dish, at
                  least.  The stability we need was
                  not there
                  the last time I looked, when you
                  factor in the twisting of the
                  fibers, the
                  diurnal temperature variations,
                  etc.  Can you give me more info on
                  these
                  wideband analog links?  It would
                  be much easier for us if they
                  really
                  worked well at these bandwidths of
                  ~10 GHz.

            Glenn is in Green Bank, I believe, but when he
            sees this thread he may have something to says
            about stability concerns at DSS-28 due to the
            fibers from receiver at the base of the dish
            and the DSP electronics in the antenna
            pedestal.
                  In any case, I agree with Jouko
                  that you should bury as many
                  fibers as you
                  have money for.  The cost of the
                  WDM systems far overshadows the
                  cost of
                  fiber at 500 meters.  If you were
                  trying to reuse existing
                  infrastructure,
                  it would be a different story.

            We don't even have to bury the fiber bundle.
             It just gets strung alongside all the other
            cables that are already there.

            Cheers

            Tom


      Justin Jonas
      j.jo...@ru.ac.za








--
Michael Inggs
Department of Electrical Engineering, University of Cape Town and 
Centre for
High Performance Computing, Private Bag, Rondebosch 7701, South Africa.
Tel: +27 21 650 2799 Fax: +27 21 650 3465
"Ex Africa semper aliquid novi"