Tank circuit impedance measurement

Once the coil has been incorporated into a tank circuit, a dip meter can be used to measure the resonance frequency. For a parallel resonant circuit, the dip meter can be used in the usual way, i.e., look for a "dip" indication as a function of frequency. For a series tank circuit, it is best to use the dip meter as an rf source acting like an artificial NMR signal and maximize the receiver output when the receiving system is fully hooked up. This will work also for the parallel tank. (See section V.C.9. on impedance matching.)... 

As already described, a magic-tee is a four port device in which two of the ports are isolated, i.e., have infinite impedance between them if the impedances at the other two ports are matched. Thus, the device can be used to match a resonant circuit to 50 Q or, for that matter, to measure the impedance at resonance of the tank circuit. The tank circuit under question will have impedance R at resonance when the output of the magic-tee, easily monitored on an oscilloscope, is an absolute minimum. (See the figure under magic-tee on p. 393.) Unfortunately, this is easier said than done because there are relative minima when the capacitors are adjusted to give an impedance which is, for example, equal to R in magnitude but with an imaginary component. When you play around with a scheme like this for the first time, it will be useful to let R be variable so that it can be adjusted for a... 

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