External reference clock "REF CLOCK" input on the USRP2


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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