Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450

[Igor Almeida]

On Fri, Aug 28, 2009 at 12:56 PM, Douglas
Geiger<address@hidden> wrote:
> That sounds like it could be a frequency offset between TX and RX. You
> say you aren't synchronized (which I interpret to mean you don't lock
> the clocks of the TX and RX together somehow) - do you have a costas
> or similar carrier offset recovery block/process on your receiver?

Correct, the USRPs are physically disconnected.
Right now, the graphs are:

sig_source_f -> float_to_complex -> head -> usrp.sink_c

usrp.source_c -> file_sink (on the other PC)

TX usrp sends the first 1000 cycles of a 2MHz sine wave (sig_source
with 4MS/s), then the "training graph" is disconnected and another one
with the QAM modulator kicks in. Both scripts tune to 2.5G.
The strange thing is no matter what frequency I set the sig_source to
(already tried 1.5k, 2k, 1M and 2MHz, sampling frequency 4MS/s), the
fft on matlab always shows a single impulse at aproximately -3kHz. In
the time domain, the signal is sinusoidal on both real and imaginary
parts, when I expect it to be only real since the carrier has (should
have) been removed.

I believe I am missing some trivial concept here.

-- 
Igor Almeida