Re: [Discuss-gnuradio] Quadrature Sampling with the TVRX

[Andrew Lutomirski]

On Wed, Feb 10, 2010 at 5:22 PM, Thomas <address@hidden> wrote:
> Hi all,
>
> I'm confused about how quadrature sampling is done with different
> daughterboards. I noticed the daughterboard FAQ says the TVRX is "not a
> quadrature board."
>

[...]

>
> I guess I am asking what the difference is between quadrature and
> non-quadrature boards and if that has any impact on your ability to get
> valid quadrature samples out. Is it that "quadrature boards" do the complex
> mixing in hardware themselves on the board and send the I and Q signals to
> separate ADCs, and the complex mixing isn't done in the FPGA in that case?

The TVRX mixes from whatever frequency you've tuned to an IF of 20MHz.
 The channel is 6 MHz wide, so your signal content is 17MHz to 23 MHz.
 The ADC samples only one channel.  The digital downconverter then
mixes the rest of the way to DC and produces quadrature outputs.

So it looks like a quadrature board from a software point of view, but
it's really not a quadrature board, and you have no quadrature phase
error.

--Andy