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    User name paschke

    Log entry time 20:48:43 on June29,2004

    Entry number 127415

    keyword=BCM behaviour

    BCMs were moved around this afternoon. Here I'm looking at data taken
    since then (Runs 2531, 2532, 2533, and 2534).
    BCM1, BCM3, and BCM8 are all read out from the same ADC.
    BCM2 and BCM7 have been moved to another ADC on the other side of
    the crate.  The question is: can we get a good double difference
    from BCMs in different ADCs?  The answer: "maybe".
    Double Difference (1-2) and DD(7-8) are both about  1.5 sigma from 
    zero, while DD(1-3) is zero, with nice lack of tails.   
    DD (3-7) is 3.6 ppm (with ugly tails) and a huge component of apparent
    readout helicity pickup (the pairsynch cut select which helicity 
    came first in the pair).  
    So, the two downconvertors really don't agree.  Helicity pickup
    previously reported in bcms 7 and 8 was coming from the bcm 
    10 kHz electronics (not from the ADC reading those signals out).  
    And while bcm1, 2 and 3 still bear watching, they at least haven't 
    been shown to be bad.
    Helpful guide to bcm identities:
    BCM1 = upstream 1x (1MHz)
    BCM2 = downstream 1x (1MHz)
    BCM3 = downstream 3x (1MHz)
    BCM7 = upstream 3x (10 kHz)
    BCM8 = downstream 3x (10 kHz)

    FIGURE 1