
One 555 is configured as a feedback oscillator through a toroidal transformer with a tuned circuit to set the frequency of oscillation. The other takes an inverted input from the oscillator to produce complimentary push-pull outputs from both 555s, which are fed to another transformer that in turn feeds a low-pass filter and thus the antenna.
via Blog – Hackaday https://hackaday.com/2022/01/13/work-the-world-on-a-555/
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