dangerd wrote:

I guess what I want to know is what is happening to that radio signal
(I think it is a UHF signal) which means that they have to convert it
to a light signal?

Also, can you beam a signal down a tunnel (40m below ground) which
twists and turns both in the vertical and horizontal directions?

The common to provide radio communication in a tunnel is to use a leakage
coaxial cable which isn't 100% shielded and has slots along in the
shielding.

Regards,

Ralf
--
Vy 73 es 55 de Ralf, DL2MRB