> > Hi Tom, > > To save money on analog fiber transmitter/receivers, perhaps you could > transmit your full 10GHz band on a single > analog fiber, or as you suggested, convert the 10 GHz band to a pair of > 5 GHz IF's, and transmit on two analog fibers. > > After the analog fiber receiver (located in the electronics lab) you > then can break the 5 or 10 GHz bands up into smaller bands > and digitize the smaller bands, or consider digitizing the full band > using a 20 Gsps ADC (but you'll have to wait for > this ADC board, or help us develop it - we are looking for partners to > drive the development of this board).
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. 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. John > > Best Wishes, > > Dan > > > > > Tom Kuiper wrote: >> Dan Werthimer wrote: >>> Can you transmit the RF or IF through analog fibers, and then locate >>> the digitizers in >>> an electronics lab, where they are easy to service, upgrade, keep >>> cool, shield from the receivers, ...? >> We can, in principal. The receiver being built first for Canberra by >> Steve Smith in Sandy's group at Caltech re-uses much of the GAVRT >> design and technology. 17-27 GHz will be converted to baseband in >> five 2-GHz bands. The conservative assumption is that we will clone >> this for Goldstone. Of course, technology is always changing. >>> At the ATA we use analog transmission over fiber. >>> Each ~15 GHz bandwidth fiber driver/receiver pair cost $2500. All >>> the digitizers >>> and digital backends are in the same room, making it easy to upgrade >>> and service. >>> >> 40 x $2500 = $100K is about the cost of the receiver. This is also >> the reason why Sandy is bringing down only half of the IFs that he >> generates in his GAVRT receiver. Do you think that, given the >> receiver design, we would want to upgrade the ADCs? >> >> Currently, the design is to bring the baseband out to connectors on >> the receiver box, to be connected with hardlines to the ADC box. >> Steve understands the need for shielding well. He works >> elbow-to-elbow with Glenn, after all, and they have tested both their >> analog and digital gear together in close proximity. >> >> ATNF digitizes at the receiver on the AT so it can be done, carefully. >>> The fastest current CASPER digitizers is 6 Gsps (8 bit); we plan to >>> develop >>> a 20 Gsps digitizer over the next year or so. Their are a some 80 >>> Gsps digitizers, >>> but we don't have any plans to use them yet, as we can't handle the >>> data rate. >>> >> When you finish the 20 Gsps digitizer, we may want to revisit the >> receiver design. Currently, with available mixer chips, we cannot >> cover the whole 17-27 GHz band but we could break it into two. >> >> Jouko's recommendation seems like a good idea. Fiber cables are >> cheap. If I understand it correctly, the single mode fibers will >> support analog if we need to go that way. >> >> Best regards >> >> Tom >>> Best Wishes, >>> >>> Dan >>> >>> >>> >>> Tom Kuiper wrote: >>> >>>> During the upcoming Goldstone 70-m down-time, we have an opportunity >>>> to put fibers dedicated to radio astronomy in the antenna. The >>>> receiver we envision would, when fully built up, have 40 2-GHz >>>> ADCs. To be able to use our signal processing equipment with other >>>> antennas as well, we would want to put it in the Signal Processing >>>> Center, which is about 0.5 km away from the receiver. I assume that >>>> we would have a 10 GBe switch in the antenna. Could someone give me >>>> an estimate of how many fibers of what kind would best serve our >>>> needs? >>>> >>>> An alternative scheme would be what GAVRT DSS-28 does, which would >>>> be to bring 40 IFs to the SPC and digitize there. That way the ADCs >>>> could serve other antennas. However, this appears to me to be more >>>> expensive and more problem prone, and ADCs are cheap. >>>> >>>> Thanks and regards >>>> >>>> Tom >>>> >>>> >> >
