Re: I am planning to beam radio signal into space.

[EMAIL PROTECTED] (sooncf) wrote in message news:<[EMAIL PROTECTED]>...
> [EMAIL PROTECTED] (P. Backus) wrote in message news:<[EMAIL PROTECTED]>...
> > 1. With a 3 m antenna you will need a LOT of power to be detected at
> > the distance of the nearest star system, about 4 light years.  The
> > equivalent of the Arecibo antenna and the Project Phoenix SETI
> > processor at 4 light years could detect a 36 kW transmitter on a 3 m
> > dish.  If you want to reach 10 light years, you would need more than
> > 200 kW.
>  
> > 2. Although directional, the antenna will dump a small fraction of the
> > power in other directions, its "sidelobes".  I think for a typical
> > antenna this will be about 0.1%.  For the 36 kW example above, you
> > will have the equivalent of an omnidirectional antenna broadcasting a
> > few watts.  People (the government) will notice.
> 
> I can built a bigger dish my self, similar to Arecibo, 
> ofcouse not that big, maybe 10 m, or even 20 m.
> It will have parabola curve, 
> not hemisphere(Arecibo is hemisphere right?).
> I believe I can do it.
> This would reduce power needed and reduce sidelobes.

A bigger dish would reduce the power requirements.  A parabolic dish
has the extra advantage of only needing a simple feed antenna. 
Because of its spherical surface, Arecibo uses line feeds or specially
shaped subreflectors.

There are probably two challenges to building a bigger dish.  First,
you must have good surface accuracy and it must maintain a parabolic
shape as you point the dish in different directions.  Second, you must
point the telescope with good accuracy as you follow a star across the
sky.  Neither problem is impossible, just tricky.

If you are really going to follow the Arecibo design, a parabolic
shape will only beam your signal straight up.  The reason Arecibo is a
spherical shape is to focus radio waves from a large area of the sky. 
The feed antenna is moved to point at different positions.

> 
> > 3. There are international agreements on radio spectrum usage.  You
> > cannot just broadcast on any frequency at any power (especially
> > kilowatts!), no matter how isolated you think you are.  If you
> > transmit on a frequency assigned to a commercial service, you will
> > hear from their lawyers and your government.
> 
> I will carefully select frequency so than it will no interfere
> with any services on earth.

Good luck.  The spectrum is pretty thoroughly allocated, everywhere in
the world.
>  
> If the ET also think like you, they never transmit high power beam out.
> Your SETI project will never pick-up any signal from the ET.

If there are dedicated individuals like you out there, it might make
our job easier.
>  
> > Peter Backus
> > Project Phoenix