More on RadPhi cables and BCAL cabling
17-Jul-2006
We need to decide on a cabling scheme this week as Chris wants to order whatever is needed soon (patch panels, converters, etc.).
Outstanding issues are cables/ends, how much delay is needed, and where we split signals. See the GlueX wiki for more information:
http://www.jlab.org/Hall-D/software/wiki/index.php/BCAL_Beam_Tests
Cables
Richard's note (on the Wiki) lists 620 LGD cables, 250 ns each, and (48+30+48+6) 80 ns prompt (running from alcove to racks) and 170 ns delay cables (coiled under the racks).
Chris and I spent all morning in the RadPhi rack area and could not locate all these cables. We found the 250 ns LGD cables and most of the 80 ns cables, but not all of them. We suspect Richard's note is incorrect, and perhaps 48 of the 80 ns + 170 ns cable pairs are actually single 250 ns cables. We traced all the cables through the trays and some non-LGD cables wind their way through the 250 ns cable loops. The leading candidates for being 250 ns instead of 80 ns are the barrel gamma counter cables.
Can anyone confirm this? If not some 80 ns cables are missing (not that we need them, though...).
The 170 ns cables under the racks are a bit of a mess, and we have not figured these out yet.
The exact BCAL cabling scheme, and what we have to order, depends on the delay needed (see below) and where we split signals (PMT or patch panel).
Delay
The amount of delay needed depends on the tagger trigger delay and the photon flight time from tagger to BCAL. Mike Zarecky (H-B engineer) said the distance from the radiator to the entrance to the alcove is:
>It's 1488.66 inches (approx.)
>Mike
or 126 ns if I did the conversion correctly. Eugene's information gives a tagger trigger delay of 360 ns assuming 80 ns between CLAS TS and the BCAL TS (this cable is being pulled today...I'll know the exact length this afternoon). 360-125 = 235 ns, so 250 ns should be ok, but I'm worried we are getting close, and I have not accounted for any patch panels and cable runs in the BCAL racks.
Splits
We need to come to closure on the question of splitters. Critical is how the two connectors in the PMT bases are wired up (Paul?), and whether a small reflection from an unterminated spigot on the base can be tolerated.
