Jay,
* If I'm not mistaken, we can get a BPM offset from a bad RF cable (probably the termination), or a very poorly matched pair of cables. It would have to be a gross rather than subtle defect to explain a 4mm offset: the equivalent of a putting a 3dB attenuator on one of the signal cables, or a 100 Ohm termination.
* Which brings me to my next point. I haven't looked at the attenuations, but I assume if we replaced the existing cute BPM RF cables on 09B with matched 3/8 heliax, we could put the front end electronics on the floor where we can SHIELD it. Hard to believe the offsets could get worse. Right now 09B may be in a 1 kRad/hour field when Qweak is taking high current. The front end box has been replaced once. The new one may only last another few weeks.
* As for the 09B harp, the noise and offset don't look that bad in your elog figure, and some of the wires are clearly present. So I'd go with the hypothesis of low gain on the preamp. Could the preamp be rad-damaged as well?
* When Mark Pitt was RC, we decided to defer swapping the unreliable 08 can (low S/N due to the large antenna spacing, but also funny offsets) with a standard one because 09 and 09B were working at the time. Of course 09B shit the bed soon after and we lost our redundancy. Next down of more than a few days, we should swap out 08.
Dave