Supplied Ferrites all have small knot in one wire

[cutty]

The pre-wound ferrites that came with my Blue kit all have a small loose knot tied in one of the two wires.

What is the significance of this?
Should this be connected to a certain pin of the pre-amp?

thanks

Connect those one with the knot to the + terminal.

The polarity doesn't matter for the Blitzortung system.  This is a TOA / TOGA system, and all it needs is stroke impulse data. The polarity would matter if this were a DF locator, which it is not.  It's good to keep 'consistent' however, since it is possible, if you do everything correctly, (Same polarity, Correct physical orientation) using two ferrites at 90° to 'eyeball' the direction of a signal on local signal display...e.g. attached.... which can help track down "interferers"