Earthed

How far can a signal from Earth be received and be understandable?

In other words, can signals be sent from Earth and be receivable by far-away sources like other star systems? We can 'barely' hear Voyager 2, not even a light year away but it's an extremely weak signal. Can 'Strong' signals be directed to other solar systems from Earth, or even regular TV systems possibly be overheard from light years away?

Public Comments

1. I know this alien. He can probably answer this for you.
2. The signals will just take longer to fully sharpen up...
3. Due to degradation from space noise, only a few parsecs.
   
   
   
   They coluld still be detected for farther then that, but they would be unintelligible.
4. I have seen an answer to your question and still haven't located it, but it was many thousands of light years for a similarly equipped civilization. The exact number escapes me, but while you rightly point out that we can barely hear Voyager 2, you forget two things which determine communications range.
   
   
   
   One is transmitted power. One can hardly put a 500 watt transmitter on a satellite. Those transmitters are much less than 100 watts. Probably on the order of 10 watts. Either you have some sort of generator (which adds weight), or you depend upon batteries charged by photocells (which also adds weight). You'd need a *lot* of extra weight in photocells and/or generators to run a 500 watt transmitter. Earth based transmitters, however, do not have this limitation (nor would a ground based alien station).
   
   
   
   The other end of the equation is the size of the antenna. I am purposely leaving out the receiver; looking for such signals I must presume that cryogenic cooling is applied to the receiving antenna and pre-amplifier. We are familiar with the old VHF/UHF antennas on houses. At least most of us are. The frequencies being used in space communications will be using parabolic reflectors. We see them all the time - for instance Dish Network receiving antennas and Direct Tv receiving antennas. This size of antenna might easily be put in orbit. They will have considerable gain (resulting in more effective radiated power).
   
   
   
   Now consider the size that we could *never* put into space. How big? Consider this antenna:
   
   http://www.naic.edu/public/the_telescope.htm
   
   
   
   This monster can generate enough gain that it can bounce signals (and hear them) off of other planets. It can hear signals from galaxies and quasars hundreds of millions of light years away.
   
   
   
   It can, as bouncing signals off of planets, transmit. Should such a radio monster exist elsewhere in our galaxy, the two might well be able to communicate. It is a matter of generating a lot of power and having a monster of an antenna with a matching monster of gain.
   
   
   
   
   
   Best regards,
   
   Jim