Wednesday, February 26, 2014

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Minimalist Dip Meter

In days gone by a radio amateur always had a dip meter close to hand in his ‘shack’. Now that people can afford oscilloscopes, the poor old dip meter has lost its importance and is  frequently no longer to be seen. Actually this is a shame because many tasks are much easier to carry out with a dip meter. Anyone who’s interested (perhaps the second time around) can easily build one rapidly with this very simple but adequate circuit. The interesting question is namely what do you actually need from a dip meter? 

Minimalist Dip Meter-Circuit Diagram Minimalist Dip Meter Circuit Diagram
  • A visual display of the dip? Nope, the ‘scope can handle that task.
  • A large frequency scale? Not necessary, as you can connect a frequency counter for this.
  • A selection of coils? We don’t need these because we can use a jumper to change range (no coils to lose any more!).
The sensor coil L1 has ten turns and is wound  using an AA-size battery as a former. This coil will allow us to over the range from 6 MHz to 30 MHz. With jumper JP1 open an additional fixed inductance of 10 μH comes into circuit. The frequency measurement range is then from 2.5 MHz to 10 MHz. The switch may be replaced by a jumper. 

To take measurements you hold a resonant circuit close to the sensor coil. Tune the rotary capacitor C1 slowly to and fro in order to find the resonant frequency, at which the oscillator amplitude decreases somewhat. The frequency can then be read directly off the oscilloscope.
To obtain a very accurate measurement you can additionally connect your frequency counter to the second output.

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