Re: [Discuss-gnuradio] Why 4 ADC's?

[Ian Larsen]

Ok, that makes sense.  Looking back at this site
(http://www.nd.edu/~jnl/sdr/docs/tutorials/4.html#tth_sEc2.1) I see
that the DDC is combining the I and Q inputs to do complex
multiplication.  I originally thought it was multiplying the I and Q
components separately, so that no input to Q would mean zero output
for Q also.

Thanks so much!

-Ian Larsen



On 7/18/07, Johnathan Corgan <address@hidden> wrote:
> Ian Larsen wrote:
>
> > I assume this also true for the BasicRX daughterboard?  (Doesn't do
> > downconversion, but does do analog multiplication to get I and Q?)
>
> Almost. The boards don't do anything with the signal, but have separate
> I and Q inputs that go to the ADCs as is.
>
> On the FPGA, however, there are digital mixers that you can use to
> convert a center frequency down to baseband, so you get a complex I and
> Q signal out of that, even if you only supply a signal to the I input.
> That is what is actually happening when you "tune" a BasicRX or LFRX board.
>
> --
> Johnathan Corgan
> Corgan Enterprises LLC
> http://corganenterprises.com


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