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

From: Jeff Brower
Subject: Re: [Discuss-gnuradio] Why 4 ADC's?
Date: Thu, 19 Jul 2007 09:37:26 -0500


> > The LFRX has two separate antenna inputs, supplied to Vin-A and
> > Vin-B.  These are not I-Q data.  USRP board FPGA logic would apply
> > one mixer or two (30 MHz or less).
> [...]
> > The RFX2400 mixes with a 2.4 GHz osc and creates one set of I-Q 65
> > MHz range signals, +/-I on Vin-A and +/-Q on Vin-B.  To get baseband
> > signals, the logic has to apply two mixers.
> The FPGA DDC logic uses a single but *complex* mixer to do frequency
> conversion of the signal from the ADCs.  That is, it treats the data
> from Vin-A and Vin-B as a complex number in I and Q format, and
> multiplies this complex number by a complex sinusoid of a configurable
> frequency.  This is very different from having two mixers.

Yes thanks for that correction.  That's accurate for RFX2400.  For the LFRX 
Vin-A and
Vin-B are treated as separate RF inputs and not a combined I-Q data set.


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