I got a little bored so I decided to do some calculations regarding space communication. All calculations are on 435MHz.
You should be able to talk between the space station and earth with two 5 watt handholds on each side even if the ISS is 2000km away and a an elevation is less than 10 degrees.
The path loss to a geostationary satellite 36000 km away is 176 db or more. You now need a small beam in both ends and a 50watt mobile transceiver.
The distance is much larger than you might think
So what about the moon? Well the path loss is 197db so you can still use a 50w FM mobile
in both ends and both stations need a long yagi.
What about larger EME stations? If they can hear their own echo using CW they are capable
of communicate to a distance of up to 600 million Km. This enables the user to communicate
with an equal station on Mars, Asteroids, Venus or Mercury. Big-gun EME stations could
If you want to communicate to Pluto when the planet is the furthest away from the earth,
And the path loss is 280db you need a 20meter parabolic dish in both ends and 1500watts.
You could do the same using simple 5 watt handholds both standing in the focal point of
a areceibo like dish.
In order to talk 4.3 light years away to the closest star Alpha Centauri, you need to overcome
a path loss of 358 db. You need a arecibo class dish both on earth and on Alpha Centauri system
and 200kw transmitter.
A week ago a planet with a similar mass and size to our own planet Earth,
likely similarly composed of rocks and iron, has been spotted orbiting a star some 700 light years away in the constellation Cygnus, scientists announced Wednesday.
This planet has a path loss off -401.6 db path loss @ 435Mhz so if there is aliens on the planet you need a 500 megawatt transmitter ( if it's possible to build one i am not sure). And an antenna equivalent to a 1km dish in both ends.
So, if some feels like criticising the SETI project. Remember how short the interstellar distance is for radio and how unlikely it is to hear anything unless some on purpose tries to contact us with a very large system, close by.