Robert Ehrlich wrote:

Eric Greenwell wrote:

...
In any case, the bearing info appears to be determined by using
two or more antennas.
...


More than 2 are necessary. With 2 antennas, you can only measure
the time difference between the 2 received signals. This time
difference can be translated into a distance difference. The points from
where a given difference is observed are on an hyperbola, which
can be considered as the same as its 2 asymptotes, as the distance
to the antennas is high compared to their mutual distance. But
to determine which of the both asymptotes is the correct one, you
need some more information, i.e. another antenna.

A more careful reading of the document shows only two antennas are used:
one bottom mounted omni-directional and one top mounted directional. It
also shows the omni-directional antenna can optionally be a directional
antenna.

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Eric Greenwell
Washington State
USA