Yttrium iron garnet

John Larkin posted a schematic that included a featureless box that he described as an ECL voltage controlled oscillator.
It was probably a voltage controlled crystal oscillator - a VCXO - or perhaps a TCVCXO.
https://en.wikipedia.org/wiki/Voltage-controlled_oscillator
They now seem to go up to 800MHz and 1.2GHz which is a lot faster than they were when I was interested.
https://www.qsl.net/n9zia/yig/yigintro.pdf
Yttrium iron garnet tuned oscillators were around back then, but their 2GHz to 8GHz range was too high for me to count with the integrated circuits around then - we had to go the Gigabit Logic's GaAs parts to get to 800MHz, and that became the unique selling point of the system.
The YIG resonance is narrow and depends linearly on the magnetic field which can be controlled with some precision.
John should have done his precision timing by counting the edges of a YIG generated clock - we now have counters that can go that fast, and twiddled the frequency to get the exact time delay required.
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Bill Sloman, Sydney