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"
