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

From: Ian Larsen
Subject: Re: [Discuss-gnuradio] Why 4 ADC's?
Date: Wed, 18 Jul 2007 16:43:31 -0400

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

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