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

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Why 4 ADC's?
Date: Thu, 19 Jul 2007 06:30:57 -0700
User-agent: Thunderbird (X11/20070604)

Jeff Brower wrote:

> 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.

Johnathan Corgan
Corgan Enterprises LLC

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