sampling theorem

i've done my sampling like this is it correct ?
i'm sampling a 3GHz signal;
design for 8 bit sample

double array[256]; //8 bit so
double amplitude=100;
double frequency=3000000000;
for(int i=0;i<256;i++)
{
 array[i]=amplitude*sin(2*PI*frequency*i/(2*3000000000));
 dc.setpixel(i,array[i],RGB(255,0,0));
}

plz guide me and explain if i'm wrong

"ravirevolt" <ravirevolt@yahoo.co.in> wrote in message
news:VdCdnSBiBPjsO1veRVn-vA@giganews.com...
>
> i've done my sampling like this is it correct ?
> i'm sampling a 3GHz signal;
> design for 8 bit sample
>
> double array[256]; //8 bit so
> double amplitude=100;
> double frequency=3000000000;
> for(int i=0;i<256;i++)
> {
>  array[i]=amplitude*sin(2*PI*frequency*i/(2*3000000000));
>  dc.setpixel(i,array[i],RGB(255,0,0));
> }
>
> plz guide me and explain if i'm wrong

Since you haven't given too much background information, I'll just comment
on what you've shown us...

What does 8 bit samples have to do with double array[256]? It appears you
are doing a simulation of some kind and it appears you have double precision
arithmetic. If you want 8 bit samples, you have to convert your array[i] to
say short ints (but that's usually 16 bits), so you'll need to do more
conversions to ensure they have only 8 bit data in them.

You sampling frequency fs here is 2*fin where fin is your sinusoid'd
frequency. I'd recommend you use fs = 4*fin or higher for your simulation
purposes (as well as in a real system). The Nyquist theorem mandates an fs >
2*fin.

Also, your time index (i) in your sine computation should be different from
your loop index.

Cheers
Bhaskar

"ravirevolt" <ravirevolt@yahoo.co.in> wrote in message 
news:VdCdnSBiBPjsO1veRVn-vA@giganews.com...
>
> i've done my sampling like this is it correct ?
Is this associated with your previous post about simulating a digital 
beamformer?

> i'm sampling a 3GHz signal;
is that your signal bandwidth or signal center frequency?

> design for 8 bit sample
>
> double array[256]; //8 bit so
have you reserved space for a 256 element double precision vector called 
array here? Why not give it a descriptive name and insert a comment that 
helps you remember what you are physically representing?

> double amplitude=100;
You seem to have arbitrarily set the peak amplitude = 100. A comment as to 
why you did this might help you interpret your code at a later date.

> double frequency=3000000000;

> for(int i=0;i<256;i++)
> {
> array[i]=amplitude*sin(2*PI*frequency*i/(2*3000000000));
now load up 256 elements with something very close to zero ?  sign will 
alternate but maybe not that reliably, why are you doing this?  What does 
your i index represent?

> dc.setpixel(i,array[i],RGB(255,0,0));
produce a short monochrome line on a display? what happens if array[2] 
is -ve by the way?

> }
>
> plz guide me and explain if i'm wrong

How can we? - you don't say what you are trying to do.

Best of Luck - Mike