> "Michael S. Lorrey" <email@example.com> wrote:
> Get real. Unless they are using only closed circuit sytems like
> fiber-optic/co-axial/twisted pair copper, No radio satellite uplinks
> (optical will only be usable in clear weather for high bandwidth),
> no broadcast tv or AM/FM or shortwave, then they will be emitting
> radio signals if they are a technological civilization. If they are
> only space based, and only use tight beam laser communications,
> they might slip through.
Interestingly enough, there does appear to be an inversion occuring in our society. Closed circuit multiwavelength fiber does appear to have the highest bandwidth and be the wave of the future for us. I think the record is now up around 40 Gb/second on a single fiber over many kilometers.
Both the military and the satellite manufacturers are looking seriously at optical ground-to-satellite up/down links because the bandwidths are higher. Does anyone know if there are frequences where the clouds are transparent that allow this? The problem is that the multispectral data volume gathered by the current generation of observing satellites is so large that it is difficult to transmit via radio.
Radio on the other hand seems to be shifting from a broadcast medium to a local communication medium. You are going to get the greatest carrying capacity out of radio if you use it in low-power cell-phone-type or last-200-yards-to-home type applications while using the high bandwidth fiber/cable carrying highly multiplexed signals over long distances.
This would seem to be due to simple physical efficiencies. You want to use the lowest power signal possible confined to the smallest possible physical space (air or fiber) that provides an acceptable S/N ratio at the receiver.
The SETI people have viewed with some dismay the rise of highly directed point-to-point channels as that means to detect the signals we are will have to be in the "line-of-sight". That means someone has to identify us and intend to communicate us or we have to be in the path of a signal between two other technological civilizations. [The odds drop yet again....]