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

From: Jeff Brower
Subject: Re: [Discuss-gnuradio] Why 4 ADC's?
Date: Wed, 18 Jul 2007 15:12:17 -0500


> > 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.

I think the OP is confused at what "signal processing" is happening on the RF
daughterboard.  Although some recent posts have said "none", there actually is 
-- filters to separate the I and Q signals which were summed at the point of 
transmission to make a single airwave.

This is why the two ADCs are actually sampling separate, different signals, even
though their sampling rate clocks are synchronized.


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