Re: [Discuss-gnuradio] I&Q on same or separate channels?

[Eric Blossom]

On Thu, Dec 13, 2007 at 04:35:51PM -0500, George Nychis wrote:
> Hi all,
>
> For the in-band code, I'm noticing that it seems like the FPGA is packing 
> two I's or two Q's, and not an I and a Q.  If you take a look at the 
> following plot of a 10MHz sine wave, you will see what I mean.  The left 
> plot is using the legacy receiver, the right side is using an in-band 
> receiver:
> http://www.andrew.cmu.edu/user/gnychis/sines.png
>
> This boils down to the following code:
> http://gnuradio.org/trac/browser/gnuradio/branches/features/inband-usb/usrp/fpga/inband_lib/rx_buffer_inband.v
>
> I'm guessing that Thibaud's original assumption was that I and Q are packed 
> in a single channel to be read from.  With a single data channel, the code 
> will only read from channel 0.  Is this incorrect?  If so, this explains 
> the behavior we're seeing.
>
> If I and Q are on separate channels, are they synchronized?
>
> - George

I and Q are not on separate channels.  They are interleaved, 
I0, Q0, I1, Q1...