Ground plane near FDC readout strip

[Elliott Wolin <wolin@jlab.org>]

Hi,

I talked with Fernando, and as many of us suspected it is not a good idea to have a ground 
plane near the cathode readout strip.  It is important to shield the entire detector from 
external noise, so the outside frame and windows should be made of conducting materials 
(and be hermetic...even small gaps can let lots of noise in).  But the capacitance of the 
readout strips to ground should be minimized, so putting a ground plane close to the 
strips is not a good idea.

I believe one can think of the ground plane as causing the preamp input to see the signal 
as being dropped across a capacitive divider with the preamp connected to the middle, so 
you want the capacitor to ground to be small so that the signal isn't lost (Fernando...is 
this correct?).


				Sincerely,
					Elliott


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Elliott Wolin
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