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

From: n4hy
Subject: Re: [Discuss-gnuradio] An interesting application for my new USRP... some input requested
Date: Thu, 26 May 2005 19:31:51 +0000
User-agent: Mozilla Thunderbird 1.0.2 (Windows/20050317)

Apologies. Poor writing. YOU do not need to insert with the "all derived from one source" system. Others, with multiple LO's etc. can use the injection of known reference method.

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


John Ackermann N8UR wrote:

I'm confused by the need to insert a reference signal and resample from that. I was thinking of just programming the four DACs (through two Basic RX boards) to each look at a, say, 10kHz wide chunk of spectrum around the nominal frequency, and then do a deep FFT of each of those streams. I'm confused by the need to inject another signal and resample. I'm sure I'm missing something, but I don't know what...


PS -- it may be you're describing what I did in the last couple of FMTs -- insert a known frequency from a signal generator within 100Hz or so of the unknown, then using FFT measure the delta between the two. That works very well, but requires me to measure only one signal at a time. I was hoping that with the USRP I'd be able to measure all four bands simulateously.

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