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Re: [Discuss-gnuradio] An interesting application for my new USRP... som

From: Larry Doolittle
Subject: Re: [Discuss-gnuradio] An interesting application for my new USRP... some input requested
Date: Thu, 26 May 2005 12:41:00 -0700
User-agent: Mutt/1.5.9i

On Thu, May 26, 2005 at 07:31:51PM +0000, n4hy wrote:
> HF sucks.  It is full of very large signals that will typically hurt 
> this kind of system (12 bit front
> end).  You have to scale to handle the largest signal and the weaker 
> ones go off the bottom, even
> after processing gain through the DDC.  If you build filters and 
> preamplifiers,  you can hook up
> single banded front ends directly to the Basic RX inputs.  These filters 
> and preamps do not have
> to be super but do need to do some selection, filtering and 
> amplification for your work.  Then
> you can directly digitize and DDC the RF.

Now that is a _good_ reason to use 4 channels of ADC.  Just keep those
narrow band filters temperature stabilized, or they will themselves be
a source of phase drift (and therefore frequency error).

> I do not view this as a thing 
> you would want to try
> with the USRP "directly" hooked  to the antenna.

If you notched out a couple of the biggest interfering signals, you
might be able to get away with it.  "Processing gain" is real, and
can work better than most people expect.  Radio astronomers use it
all the time.

     - Larry

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