The CMOS 4000 range have very fast rise and fall times, are very low power used ubiquitously throughout the electronics world. The field produced by the inductor generates interference which is transmitted at very low power about 1cm away from the inductor. The output signal is shown below:
The whole circuit can be built on a small breadboard with the inductor used to inject the signal (magnetic coupling) into the device under test. To minimize frequency drift the circuit can by powered from a 78L05 regulator, or simply powered from a 9V battery. Nominal frequency will drift due to falling battery voltage.
One way to see the nominal frequency is with a frequency meter. An alternate method is to perform a FFT (fast fourier transform) in the frequency domain. If you have one of the modern LCD oscilloscopes it may have an FFT function. The other way as shown above is to use LTspice to produce the FFT for you.
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