# 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?

## closed as too broad by TildalWaveNov 15 '14 at 16:43

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• 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. – TildalWave Nov 13 '14 at 16:16
• You can always get a bigger dish, so there is no absolute ceiling... – PearsonArtPhoto Nov 13 '14 at 17:38
• Also depends on how noisy are your neighbors. :) – TildalWave Nov 13 '14 at 18:11
• Modulation will also make a difference ... AM, FM, PM? – Everyone Nov 15 '14 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. – TildalWave Nov 15 '14 at 16:01