I am thinking that the point of putting the nano in an enclosure is to stabilize the
poor isolation, not necessarily to eliminate it. But when the nano's leak is stabilized,
the ISOL CAL should then enable good correction.
This assumes that what goes outside the enclosure is done with good quality
cables (at least with respect to leakage) that are terminated. It would probably
help to terminate the ends in items that roughly duplicate the impedances that
the DUT will provide, although this is admittedly not very practical in most
cases.
BTW, SMA(M) cables that are left dangling with nothing connected can exhibit
wildly variable leakage from the ends. The center pin is coupled capacitively
to the nut, whose contact to the main body of the connector can range from only
fair to non-existent, depending on how it is laying (i.e., on what forces are acting
on the nut and from what directions, etc). RF leakage of this kind leads to RF
currents on the outside of the cable, which can resonate at various frequencies.
radiate to nearby cables that are similarly indisposed, etc. So even if you can't
spare good terminations, at least screw each cable end onto something that is
well-shielded for the isolation CAL step.
Dana
