Szczepan Bialek wrote:
Today, transmitters are often very small and still they work OK without
any earth connection.
How large should a "large conductor" be?

Adequate to electron emission.

Transmitters do not emit electrons. They emit electromagnetic waves.
You only see electric current in the feed to the antenna, not externally.
When the antenna is not driven relative to earth, this is not causing
current into the earth, and so no connection to earth is required.

Probably it is the coax: "Many conventional coaxial cables use braided
copper wire forming the shield".

The transmitted signal flows only along the inside of the shield of the
coax. The outside is supposed to carry no signal. If it does, there is
a problem with the antenna system.

The outside is the "large conductor".

But in my cellphone, the coax feeding the antenna is maybe only 1cm
long, or even shorter. How can you call it a "large conductor"?

I also belive in each Tesla's word. He discovered that in his secondary
coil
is the oscillatory electron flow from the earth into the air.
Why is it impossible?
S*

We do not operate our transmitters in the region where electrons start
flowing into the air, because we do not like arcing. Tesla did, but he
was in a different business.

Electron do not start.
Electrons are flowing into the air (and vacuum) at each voltage.
The thin wire is the best "cold cathode".

What current do you measure in a wire connected to your 12v car
battery, and hanging freely into the air?
This is the current caused by your electrons flowing into the air.