USPR2 set freq.Offset

hallo list,
i’d like to setup an OFDM System using 2 USRP2. while this i getting two
Questions.
( 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

lars


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