Did you know those Serbian decoys used with Neva,

Yes

are they more compact (mean without this big box, which must be digged). I've seen only the transmitting devices, which are similar to those of the "Doubler" (you post them too in this topic once...).

Yes, they were much more compact, but not emitted the same waveform.

I think that they are connected straight to tne Neva cabin?

They were operated from the UNK van, by an extra guy, standing behind the commander.