Typical spectrum analyser screen, showing the internal 10MHz marker calibration signal which can be used for a sufficiently accurate frequency measurement to calculate the inductance.
Circuit diagram as I have built it.
Spectrum at output of crystal oscillator and doubler. Scale is about 60MHz (right hand side) to about 80MHz (left hand side). The peaks labeled 60 and 70 are harmonics of the 10MHz marker generator in the spectrum analyser. Note two "sideband" type signals of the 72MHz signal, which are marked with a question mark. "Ghost" image is caused by flyback of the ramp generator in the spectrum analyser, and really I should put a blanking circuit in.
G0UPL's kitchen table! Fredbox in the foreground. Behind that (roughly left to right): PSU, loudspeaker, HF receiver, spectrum analyser, 1-valve 80/40/30/20m CW TX, ATU, Heathkit 'scope, HP1741A 'scope connected as spectrum analyser display.