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 <[email protected]>
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
[email protected]
--
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"
