GShV is an ECCM fix against AM-modulated jamming. For the first time, this technique was introduced into C-25 Berkut, later - into C-75 Volkhov and C-125 Neva systems. In Berkut, this mode was called GSh, in Neva - GShN. I guess that the abbreviation GSh stands for the Russian "Gashenie Shumov" - that is, "noise reduction", letters V and N means the implementation in Volkhov and Neva systems.

In a nutshell, GShV is a side-lobe blanking and AM-demodulation scheme, that is based on comparison of the signal from the narrow-beam antenna, epsilon or beta (this is called main channel) with a reference signal coming from the wide-beam antenna (this is called auxiliary, or compensation channel).

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1) since GShV needs main/aux channels with narrow & wide beam antennas, in Volkhov it can be used only in LORO ('Podsvet') mode.