Uhd_fft.py and USRP N210

GNU Radio
1

Hi,

I was running uhd_fft.py on USRP N210 with TVRX2 daughter-board. I get
mysterious peak at every 100 MHz center frequency i.e. 100MHz, 200 MHz,
even though no antenna is connected. Please help me what is wrong.

Thanks you,
Rahul

2

Hi,

I was running uhd_fft.py on USRP N210 with TVRX2 daughter-board. I get
mysterious peak at every 100 MHz center frequency i.e. 100MHz, 200
MHz, even though no antenna is connected. Please help me what is wrong.

Thanks you,
Rahul

Two things:

There is almost always an anomaly near DC, so it’s often best to tune
your target frequency so
that it’s away from DC in the baseband. So, let’s say your signal of
interest is at exactly
500MHz (just to use the example from problem.png), tune 50KHz away,
500.050MHz, so that
DC appears outside your passband.

The clock oscilator on the USRP2/N2XXX is 100MHz, so there will be small
spurs of this clock
appearing, but which are usually easily drowned out once you put an
antenna on the input.

3

On 06/02/2011 03:06 AM, rahul sol wrote:

got peak at other frequencies, which didn’t happen with XCVR.

Moreover, SBX is also giving weird results. Although the network
analyzer is transmitting at 952 MHz, I got peaks at 948 & 952 MHz.
It’s like mirror image around the center frequency. I tried in all
possible band, in both TVRX2 & SBX but the results are same.

Thank you,
Rahul

Rahul:

Your TVRX2 plot looks very much like you’re driving it into the clipping
region, which will produce
massive amounts of harmonic content. Try turning down the gain, and
reducing the output of your
signal generator.

For the SBX, I’m not sure what might be going on there, but again, you
may be running into a clipping
issue.