Source: http://www.space.com/8946-dog-days-summer-celestial-origin.html
However, direct messages can be sent using amplified power (in a narrow beam), and as a result, will take much longer to degrade. These short bursts are able to reach other star systems just fine, but require specific aim of the transmitter.
Source: http://zidbits.com/2015/11/where-are-all-the-aliens-what-is-fermis-paradox/