- If the tuned circuit of an lightly oscillating valve LC oscillator is brought near
(coupled with) a tuned circuit with the same resonant frequency a
dip in the grid current will occur
- This is the principle of the GDO, though nowadays
it is a dip in base current or drain current of a transistorised unit
- As a dip in current indicates resonance, a GDO is often called a Dip Meter
- The unit has a series of plug-in coils and a calibrated
tuning dial to vary frequency, allowing a wide range of
resonant frequencies to be measured
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