[rescue] Radio DF equipment (was Ham radio license question)

[James Sharp]

> antennas.  The only question about those Doppler kits
> is...are they really using the Doppler effect?  (They do
> work whatever they use.)

They do use the dopper effect.  By electrically switching between the
antennas fast enough, the antenna system becomes a single virtual antenna
that is being swung about the circumference of a circle that can be
calculated by the switching frequency & the reception frequency.

Picture someone swinging a noise maker at the end of the rope.  As the
noisemaker approaches you on the swing, doppler shift increases...it
decreases as the noisemaker swings away.  Same concept, except the
noisemaker is stationary & the receiving point is moving.