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Poor Low Frequency Data with Multiport Extension? (N5230A/U3042AE12)

Question asked by mhreider on Dec 3, 2012
Latest reply on Dec 4, 2012 by Dr_joel
I'm currently having some erratic behavior occurring with one of our 12-port extension setups we have in our lab. 
This is an N5230C mated to a U3042A E12 unit on the FW 09.46.xx. I'm getting some relatively poor data on all single-ended pairs under ~1GHz.

Interestingly, this behavior only shows up when the 12-port extension is enabled and across all ports. 
So far I have tried:
Reverting to old firmware
Trying different electronic calibration units
Swapping jumpers around (of course this wouldn't help, since its plaguing all measurements)
Double-checking that our error terms seemed reasonable (and they do)
Running through the troubleshooting guide for the 12-port extension with no power holes to be found. This would've been my first guess, as we've had problems with it for this very reason in the past.

I've attached two images: one with calibration on, one with calibration off comparing the Analyzer's performance with and without the jumpers/multi-port enabled. I used S21 to show that this isn't an issue just with ports on the extension, only when the jumpers are run through the multi-port. As I've said, this is plaguing any thru on ALL ports. The DUT in this case is a small thru trace on one of our calibration boards. 

Is there anything else I can investigate in order to isolate the problem, or is there any idea as to what is going on? 

I've also supplied the .s2p files I took, though I can supply an .s16p file where I caught this behavior as well. 

Any help would be appreciated