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RE: Re: starship-design: It's a bad, bad world out there

On Monday, October 27, 1997 9:25 PM, David Levine 
[SMTP:david@actionworld.com] wrote:
> Is this necessarily true?
> Ref.:
> http://www.landfield.com/faqs/astronomy/faq/part6/section-13.html
> How far away could we detect radio transmissions?
> The idea behind this part of the sci.astronomy FAQ is that detection of
> normal radio and television signals at interstellar distances is a myth.
> Math is included.  One summary quote:
> "Even a 3000 meter diameter Radio Telescope could not detect the 'I Love
> Lucy' TV show (re-runs) at a distance of 0.01 Light-Years!"

So what you are saying is that it is really a matter of power, beam width, 
and frequency. Typical broadband transmissions such as TV just don't have 
the range, and with few exceptions, narrowband transmissions aren't 
carrying any signal which could be unequivocally artificial.

Something else occurs to me - signal to noise ratio and signal format - 
conventional broadcast formats might appear to be simple noise at inters  
tellar distance due to signal degradation

> Narrowband radar is apparently much easier to detect, but will be short
> in duration and non-repeating.

Microwave transmissions are in the radar range and have a much higher 
signal to noise ratio, but I still think the distances involved would 
reduce the transmission to noise. Perhaps if the transmission was digital 
the range would be greater?

> I don't know how easy to detect the EM leakage of a power-grid would be,
> but it doesn't sound likely.

It requires a long wave guide with the receiver end positioned within a few 
feet of the source, otherwise it is drowned by noise. In other words, you 
can detect power leakage with a simple radio, but it is almost impossible 
to localize it without a lot of work. At any range over a few hundred feet, 
it gets lost in the background noise and is effectively undetectable.