Loops in real life
Real ground and with surrounding objects and with noise source
In real life we do not have the loop in free space and we do not have ideal noise sources.
That’s why in most cases we do not get the maximum feasible depth of the null !
The effects we see in real life are the same for the small, medium size and Alford loop.
The medium size loop differs only in the unwanted horizontal polarised component caused by the dipole mode and the resulting elliptical/circular polarization.
The depth of the null is affected by the ground reflection. A horizontal component of the noise source when reflected by the ground arrives not perpendicular to the loop (Y-axis). The phase and magnitude depends on the height of the loop and noise source, the distance, the frequency and the ground properties.
So also a phase difference of for instance 90 degrees with the vertical component of the noise source is possible (= elliptical polarization).
In real life the radiation pattern of the loop can be distorted by coupling with other objects like feeders, poles or antennas. The phase difference of this contribution can be anything, so also for instance 90 degrees.
In real life a noise source is not a ´point source´. For a deep null the source needs to be small and/or distant. Coupling with other objects causing duplicate sources also reduce the depth of the null. The phase difference of this contribution can be anything, so also for instance 90 degrees.
Conclusion: there is no guarantee that you get a very deep (40-60dB) null.
Far field radiation pattern with ground.
Of course the radiation pattern with ground of the medium size loop and of the Alford loop will also be different especially on the higher frequencies.
Far field 3D plot medium size loop (1.3*1.3mtr) over ground @28MHz
Far field 3D plot Alford loop (1.3*1.3mtr) over ground @28MHz
Last update: September 24, 2006