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[Discuss-gnuradio] external reference clock "REF CLOCK" input on the USR


From: Steve Mcmahon
Subject: [Discuss-gnuradio] external reference clock "REF CLOCK" input on the USRP2
Date: Sat, 6 Nov 2010 14:16:01 -0700 (PDT)

Hello:

I have four USRP2 boards, each with a WBX board, and I have them setup to do 
the following for a ranging algorithm application:

USRP2 #1: 901.001 MHz Tone Generator
USRP2 #2: 901.002 MHz Tone Generator
USRP2 #3: Capturing both tones and writing to file
USRP2 #4: Capturing both tones and writing to file

Each USRP2 board is connected to an antenna, so this is all over-the-air, not 
over Coaxial cable.

When I capture the tones, or look at the output of USRP2 #1 and #2 on a 
spectrum analyzer, I notice they're not always exactly where I expect them to 
be, and this makes it hard to capture them and write the data to a file. I 
understand this because of the clock variability (clock drift) on the USRP2, 
and also because the four clocks are not synchronized together to a common 
source. Can I fix this and get absolute frequency precision by using the 
external reference clock "REF CLOCK" input on the USRP2? The "REF CLOCK" input 
takes a 10 MHz sine wave, 1 volt peak-to-peak, right? I have an HP signal 
generator, so could I use it to generate a 10 MHz sine and split its output 
four ways to each USRP2 board, right?

Thanks for your help vetting out my ideas and my setup!!

Steve McMahon




      



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