Z zaskoczeniem odkryłem, to się dzielę:

https://en.wikipedia.org/wiki/Barkhausen%E2%80%93Kur
z_tube

The first experimental microwave relay system, a 1.7 GHz link 40 miles
across the English channel in 1931, used a Barkhausen-Kurz tube mounted
at the focus of the 10 foot dish shown. It had a radiated power of about
1/2 watt.

Pozdrawiam, Piotr