POOR MAN's TEST EQUIPMENT

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GRID DIP METER MILLEN 90661
measuring instrument to measure resonant frequency of radio frequency circuits. It measures the amount of absorption of a high frequency inductively coupled magnetic field by nearby objects. It is an oscillator whose amplitude changes when near a resonant circuit which is tuned to the frequency the oscillator generates. At the heart of the instrument is a tunable LC circuit with a coil that serves as a loose inductive coupling to the measured LC resonant circuit. Resonance is indicated by a dip in the meter indicator on the device, usually based on a microammeter.
  Usually measure the properties of resonant circuits, filters, and antennas.

 adverdising  of the model 90662


video: how it works
https://www.youtube.com/watch?v=_pgQq9IxZy0

manual (90651 model):
http://www.k7jrl.com/pub/manuals/millen/90651/90651.pdf
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