cable

[Gerard Visser <gvisser@indiana.edu>]

Hi Joe,
	I have been making measurements on the cable sample (the 25-pair cable 
for FDC/CDC readout). Definitely I am coming to the conclusion that it 
would be _better_ [I don't say it is _necessary_, just better] to have a 
better quality dieletric in the cable - the current design uses PVC and 
this has a high dielectric loss and furthermore the loss is 
significantly temperature dependent. The end result is, it will be 
rather difficult to cancel the frequency-dependent losses in this cable 
with a simple analog circuit. Of course, we might consider using digital 
tail cancellation (which can be adjustable, unlike the analog version), 
or we might just live with it. I'm not ready to draw any final 
conclusions on this yet.
	But I am at a point where I think it would be worthwhile to make a cost 
comparison between the present cable (our default choice) versus one 
where the wire pair insulation is a better material. Everything else 
about the cable can remain as it is, in particular the outer jacket 
material can certainly remain PVC.
	Since you have handled all the recent discussions with Amphenol, it 
would probably be best if you could make this inquiry.
	Specifically, I would like to know whether they can make version of the 
cable with better dielectric on the wire pairs, either FEP or any other 
material they can recommend. FEP is a far superior dielectric material 
(loss factor 0.0005 vs. 0.025). There are probably other choices. Their 
halogen-free cable uses polyolefin, I don't know its dielectric loss 
factor, probably it is better than PVC though. We would be happy if the 
dielectric loss is 10X lower than this present PVC cable, and relative 
temperature dependence no worse than PVC. So, we're asking for a 
dissipation factor of 0.0025 or better, I think.
	If they can make such a cable, of course the question is then how does 
the cost compare? If it doubles the cost I suppose it will be out of the 
question...
	Can you make inquiries? Or if you prefer I ask them directly, let me 
know, and tell me who is your technical contact person for the cable.
	Thanks,

	Gerard