Are the regions of insrability "always" the shaded region?

Are the regions of insrability "always" the shaded region?

- Assuming correct operation, the unstable regions

are always supposed to be the shaded ones.

I believe there were some known instances of

odd results on rare occasions (when the radius of the

circle was mathematically very large). Not sure

if that was addressed for v604 or not. If question

arises, concrete way to check is to display SB1 SB2

on a table (not on Smith Cht) then use the HELP

info to deciper what's shown in the table for

given frequency point- this can be used to verify

stable / unstable.

However, it is suggested that one verify this by running a simulation using a port impedance of, say, an impedance in the shaded region and looking at the reflection coefficient to verify that this region is in fact one of instability. Or, look at S11/S22 (see if they are above zero dB) and see if the origin of the chart is shaded or not (it should be shaded if they are above zero dB).