# How far do the omnidirectional Earth transmissions (TV, Radio, etc) travel before they become indistinguishable from background radiation? [closed]

When radio signals leave earth, they propagate out in a wave form. But how far they can “spread out” over distance until they become indistinguishable from background noise?

• Related: How big is Earth's sphere of broadcast influence? Also, could you please edit to clarify your question? As it is, it's rather broad and open to interpretation. For example, radio signals at different transmit power output, wavelength, even solid angle of its main lobe or where they were transmitted from and in what direction will effectively have different signal to noise ratio at some specific range, location even. It also depends on technological ability to discern signal out of it. Commented Nov 13, 2014 at 16:16
• You can always get a bigger dish, so there is no absolute ceiling... Commented Nov 13, 2014 at 17:38
• Also depends on how noisy are your neighbors. :) Commented Nov 13, 2014 at 18:11
• Modulation will also make a difference ... AM, FM, PM? Commented Nov 15, 2014 at 15:45
• @Everyone Actually no, not for attenuation at least which is given as $\alpha [\text{dB}/(\text{MHz} \cdot \text{cm})] \cdot \ell [\text{cm}] \cdot \text{f}[\text{MHz}]$. Actually, the question doesn't even clarify if it's merely about detecting a signal and inferring its artificial nature, or also discerning its meaning. Modulation might have a role with the latter (some are easier to flatten-out with interference of strong natural radio sources), but might not be even relevant. What's odd tho is that nobody voted to close as unclear / too broad. Commented Nov 15, 2014 at 16:01