For transmitting purposes there is a high voltage across that capacitor.
I have a friend who uses 10,000 volts rated capacitors in a loop for 50
watts.

The 1 farad capacitors are generally very low voltage.

switcher wrote:

when the metal plates move and more surface is used/covered by the cap,
is the capacitance higherb (farads) ??

I see that with loop ant, the more the plates cover each other, the
lower the tuned freq is ...

So with a high cap, you could make an ant with less turns of wire ...

Sometimes I find a large cap (1 F) at flea markets, for 1 euro/$ or so.

They cost 100 or so new. Would they make sense ??