Stealth* planes are the REAL
ghosts of the last century.
Here are some publicly available and collected data for you to calculate with...
1, S-125M Neva manual page 39...
... contains Serbian account for the detection range of the F-117A with P-18 (Spoon Rest).
2, S-75M3 Volhov manual page 18 contains detection range of the MiG-21 with P-18 (Spoon Rest).
3, As the standard WarPact target MiG-21 has 2,2m Radar Cross Section, now you can calculate the REAL RCS of the F117A, using this...
http://en.wikipedia.org/wiki/Radar_cross_section4, As you have the RCS detection capability of the SAM Fire Control Radars against standard WarPact target (MiG21), now you can calculate predicted maximum detection range against the F117...
(S75M3 - pg22/23, S125M - pg12, 1S32M2 - pg16, 5N62VE - pg13)
*I only discuss the F-117A capabilities here, that is already withdrawn from service.