E614 Cabling, Preamps & Postamps        Aug. 19/97

Noise Problems

There are some concerns that the Fastbus crate may be introducing
some noise into the wire chamber stack and/or the preamps. This will
have to be confirmed, possibly on the bench. My feeling is that most
of our noise problems are probably due to ground loops resulting in
some RF pickup. To reduce these problems in the future, it is
important that we attach all equipment to a common ground and AC power
source.

Preamps

As l'm sure Vladimir will agree, soldering the microcoax cables to the
VTX preamps was a very time consuming operation. lt would be much
better if we could make this interface a detachable connector or
alternately have "banks" of preamps mounted on "motherboards" with
output connectors for the microcoax assemblies. The microcoax
assemblies would then be routed through a hole in the endcap and
ultimately to the postamps. Pierre can explain this "motherboard"
concept.

Also, in our test configuration the DC power for the preamps was
delivered to each preamp via a coaxial cabie with a relatively small
gauge conductor. This may have also introduced some ground loop
problems. ln the final configuration, we could deliver the DC to each
motherboard with a fairly heavy gauge shieided cable from a DC supply
mounted directly onto the detector stack endcap.

One other possibly problematic aspect of our test configuration were
the short pieces of microcoax that were used to attach the preamps to
the chamber. The ground of each input channel of preamp was taken from
the chamber ground to the preamp ground via the braid of the
microcoax. The "motherboard" concept would eliminate this undesirable
situation.

Postamps

As discussed at a previous meeting, we would implement Vladimir's new
postamp design using a "VME-like" module housed in a 19" sub-rack
assembly. The microcoax cable assemblies from the preamps should be as
short as possible and the best location for the rack of postamps would
be the platform we used for the test. We coufd then run the ECL logic
cables to the Fastbus data acquisition which could be located on the
platform or outside the area if we determine it to be a proximate
noise source. The bundle of ECL cabies should be suitabiy shielded.

Grant Sheffer

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