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.
Over the years the humble 555 timer has been used in so many unexpected places, but there’s a project from [Frank Latos] which we think may be a first. On a piece of stripboard sit a pair of 555s, and instead of the usual passives there are a set of LC circuits. This is no timer, instead it’s a CW (Morse) transmitter for the 80 metre amateur radio band.
via Blog – Hackaday https://hackaday.com/2022/01/13/work-the-world-on-a-555/