USRP1 waveform

GNU Radio
1

Hi, All,

I’m using USRP1 with XCVR2450 daughterboard.
I transmit packets with OFDM modulation as in benchmark_ofdm_tx.py.
Using usrp_fft.py I detect the wave form as
http://www.cse.msu.edu/~huangpe3/music/usrp_fft.png

The two edges are attenuated a lot and there is a spike in the middle
(DC offset?)
What are the reasons for them and can I address them by updating
firmware or something else to get better waveforms as those obtained
from USRP2?

Changing the inerpolation rate changes the (frequency) bandwidth.
I know that higher data rate results in wider bandwidth.
But here the output rate is fixed by DAC 128 MS/s. Why the bandwidth is
changing in accordance with the interpolation rate?

Thanks a lot for helping me out!

Regards,
Pei

2

On Tue, Feb 15, 2011 at 11:31 AM, Daniel D. [email protected]
wrote:

or something else to get better waveforms as those obtained from USRP2?

Yes, you will see a DC offset, but the rest of that looks wrong. You are
probably sending too wide of a signal, which is getting hit by the
half-band
filters.

What is the command-line you are using to set the interpolation rate and
number of subcarriers?

Tom