The two antennas behave as one, a director with a reflector, with a null in
the radiation pattern. Varying the phase and magnitude controls have the
effect of rotating the antenna pattern and varying the spacing between the
two elements.

Orientate the noise antenna in a different direction to the main antenna and
if you know where the noise source is located then maximise noise pickup
from the noise source. There will be one null only if there is one noise
source. And usually you can consider yourself lucky if you can find it.

Another tactic is to arrange for the noise antenna to pick up a minimum of
the wanted signal if you know from where it is coming. If the main antenna
is outdoors and high in the sky and the noise source is very local, ie., you
are in the noise near-field, then install the noise antenna indoors at
ground level.

A null is impossible if signal and noise arrive from exactly the same
direction. If from nearly the same direction then the wanted signal will
decrease almost as much as the noise. But the situation can usually be
improved yet again by changing orientations of one or both antennas.

If the main antenna picks up stronger noise than the noise antenna then a
null can be obtained only by increasing gain in the noise receiver.

Its all a matter of phase and magnitude.
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Reg, G4FGQ