Re: [Discuss-gnuradio] OFDM spectrum with power rolloff?

[Matt Ettus]

On 07/23/2010 09:38 AM, George Nychis wrote:

> One last question still, do you know where I am missing a factor of two
> here:
>
> 1) My calculation of the bandwidth of the 100 active bins, and the
> actual bandwidth, is off by a factor of two:
> (((100 MHz) / 32) / 1024) * 100 = 305.175781 kilohertz, where 32 is the
> interpolation rate, 1024 was the size of the IFFT, and 100 is the number
> of active bins.  I see 610KHz, however.


The math looks right to me.  Make sure you're using complex signals and 
a complex FFT.  Also, check carefully that you are putting your complex 
signals in consecutive bins.  If you were to put signals in every 2nd 
bin, the spectrum would look twice as wide and you wouldn't see the holes.

Matt