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I recently looked at a reference design for an 433MHz transmitter and noticed that inductor orientation was specified (using the DOT). On the pcb layout the inductors are placed close, so they will probably couple electrically and magnetic. But is the orientation mainly to cancel EMC (magnetic) or voltage induced?

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    \$\begingroup\$ Please add an circuit diagram to your question \$\endgroup\$
    – jippie
    Mar 6, 2013 at 19:51

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Most of the magnetic field lines exit the inductor along the axis of the cylinder, so inductors will couple more strongly when parrallel one after another.

Likely to be more weakly coupled:

enter image description here

Likely to be more strongly coupled:

enter image description here

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A dot on a single inductor makes no sense. Dots are used to specify the orientation of the magnetic coupling between two or more windings. If your schematic had a dot by one inductor, then there is probably another inductor or winding in the same package. There is no standard way to specify relative orientation of two discrete inductors on a schematic. This would need to be done with a special note for that purpose on the schematic or a separate document given to whoever does the layout. Ultimately the layout defines the relative placement and orientation of discrete parts.

If you want to minimize inductive coupling between two discrete inductors, then you either put them far enough apart so that the external fields are attenuated enough to ignore, or you put the two in a "T" arrangement. A T is only possible if the axis of the coils are parallel to the board. If they are vertical, then this is not a option.

Shielded inductors help in this regard because the "shield" provides a nice path for the magnetic flux lines to return so that very little of the external field will return thru the air.

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