*** Apologize for mistake: resending with proper subject line *** Pete, I meant very simple thing. Realness together with assumption about analytical behavior at very low frequency can be used to roughly estimate if we have or have not enough data points close to DC. Theoretically, there are two scenarios. First, the dependence can be thought as a function analytical in vicinity of s=0. Then, real part must approximate to a constant level as low order even polynomial in f: R(f) = S0 + S2*f^2 + ... and imaginary part as odd polynomial: I(f) = S1*f + S3*f^3 + ... If low frequency data points exhibit such behavior, and we see that real part approximates to a constant level (S0) while imaginary turns into a straight line pointing to the origin I(f) = S1*f, then we have enough confidence in predicting what should be at f=0. If the function we represent has no derivative in s=0 [example: s^(1/N), in particular, sqrt(s) used in skin effect description], we don't observe such behavior, regardless of how close we are to DC. This case is difficult to differentiate from when the underlying function is analytical but the low frequency portion is missing. Fortunately, these are not frequent cases for measured models. Thanks, Vladimir >7) I'm not sure what Vladimir was talking about regarding realness from >s-parameter data. Whenever you inverse transform to get >back to the time domain, you enforce realness by producing the negative >frequency data as the complex conjugate of the positive >frequency data provided. Vladimir, if you can explain this further, I'd be >interested to know what you're thinking. ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu