Alien radio signals

[acey]

If aliens were broadcasting FM radio signals, would SETI be able to detect and decode them?

[Milamber]

Only if they were nearby - FM is pretty much a local system.

Arthur

[acey]

But apart from signal strength, I'm wondering if SETI looks at bands of frequencies in a way that would detect a frequency modulated signal. And whether it's the kind of thing that can be unscrambled if, eg, you don't know that it represents a sound or TV signal.

Putting it another way, would aliens really be able to tune in to our radio broadcasts if they don't have our sorts of radio sets?

[rigdoctor99]

Well, lets start with the simple facts.. FM is a mode or methode use to modulate the carrier of a radio signal, so if the frequency was in the 1400Mhz range then the SETI team should be able to 'decode' it.

Arthur, I think you are thinking of the VHF FM radio you listen to... This may seem 'pretty local' but that is because at that frequency it has a small wavelength (around 1M) and so is not normaly reflected by the atmosphere, but continues of out into space........ Hope this helps

[acey]

For a 1400MHz signal, how wide is the range of modulated frequency? (In theory it could be infinite - I confess I don't know anything much at all about such things in practice!).

[rigdoctor99]

For a 1400MHz signal, how wide is the range of modulated frequency? (In theory it could be infinite - I confess I don't know anything much at all about such things in practice!).

The wavelength at 1400Mhz is 21.4cm, as to how wide modulated frequency would be; That is a question that will only be answered when or if a signal is detected........ Nobody knows what the signal will look like, all that they know is what the cosmic background noise sounds like and anything that is outside of that noise needs to be checked.

[acey]

Well, that's kinda my point. Actually they know what a lot of non-background signals look like (eg Hydrogen emission, which I believe was the first frequency they checked). But a frequency modulated signal will be carrying information at lots of different frequencies over a certain range (that's what FM is) and I'm wondering how SETI samples all those different adjacent frequencies, compares them, and figures out if it's just noise or something else. Or maybe they don't.

[Tim]

I reckon its quite possible that our neighbours in Andromeda have intercepted transmissions from BBC Radio One. But they stopped recording it when no sign of intelligence was detected in the signal..........

[proflight2000]

I love tuning in my shortwave radio and hearing all the hiss and stuff. I also learned the other day that the crackle etc on an untuned tv is actually space noise. Thankyou the national geographic channel.

[EA2007]

'electromagnetic noise' from Earth hasn't reached very far, only around 50 light years and even then it is only the most powerful broadcasts which can make it truly into what we would determine as outer space.

The issue relies on what is known as the San Marino scale, which I think is numerical based from 0 (being lowest power) to 10 (being highest power), the first broadcast to reach a level high enough to escape the Earth's atmosphere was the Olympics in the 1930's (the one with Adolf Hitler attending) and I think reached a scale level of 5, nowadays most broadcasts are of a level 3.

So if aliens were broadcasting, they would have had to be:

a) emitting for a very long time, on a scale of thousands or even millions of years.

emit is such a fashion that the signal was strong enough to get to us.

c) the probability that they can understand radio technologies like we do is probably quite good, if you use us as a benchmark for the standard across the universe then the probability is quite high....something known as the 1+1 theory, whereby if there is one of something, be it an object etc, then there must be one of the other OR the opposite, i.e. matter and anti-matter.

[proflight2000]

I hope then that they have refined DAB in their estimations.