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[Discuss-gnuradio] USPR2 set freq.Offset

From: larst
Subject: [Discuss-gnuradio] USPR2 set freq.Offset
Date: Mon, 27 Feb 2012 04:56:56 -0800 (PST)

hallo list,
i'd like to setup an OFDM System using 2 USRP2. while this i getting two
( currently there is no external 10MHz generator connected. however, hope it
will be working) 

1. To achieve my goal,first i want to compensate the freq.offset and figure
out (with usrp2_fft.py) a ~40kHz difference. Now i want to set this in my
GRC workspace but it is not working.Using the GRC USRP2 wrapper and modified
the LO Offset option with 40e3 and generate, i can't see any response. Does
"set_lo_offset" work, i'm sure? What is the problem?

2. Second, to figure out the offset i transmit a simple 1k sinus with amp
0.8, decimation 200 and TX/RX Gain 0. On RX Side i see a main peak(~-44dB)
with freq.offset and some additional small peaks(~-68dB) while noise is
~98dB. reducing  the sinus amp to 0.1, only the main peak with ~-60dB exist.
When i raise the RX Gain(amp=0.1) the same effect occurs by around 15dB,
peak is ~-51dB. Is this a normal behavior or is something wrong with my
Daugherboard/USRP2 amplifiers.

My Setup: 2xUSRP2(hw=0x0400) with RFX2400 , Gnuradio is latest from tom
branch dig_ofdm

thanks for any hints


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