Nog wrote:
There are many ways to modulate a signal, compress or encrypt onto an RF
carrier but you still need RF to carry the signal if you use RF at all.
We need to detect a carrier before even thinking about decoding it.
Alien carriers may be below radio or above radio into light waves but they
will be waves of energy that will have to propagate thru space to reach us.

I don't think electromagnetic waves are a must. I agree with the other guy that
possibly particles like neutrinos could be used, possibly previously paired
and transmitted quantums, gravity waves, whatever.

And that leaves out the whole dark matter/energy stuff which could open up
a whole host of means of communicating.

Still, RF is the only thing we can scan so far, so I think we should continue
that at least until we figure out something better.

Lots of Greetings!
Volker