On 21/02/2023 08:43, claudio.franch...@tlrnet.eu wrote:
Hi Dor,
if the 6kHz spurious from the carrier are discrete, it
has nothing to do with phase noise, but rather could be residuals from
fractional divisions of the NCOs. On the other hand, with reference to
the measurements reported in the document that you find here
https://files.ettus.com/performance_data/ubx/, on page 230 and 385, it
can be seen that the output power with 15dB of gain should be around
to +5/+6dBm, at least that's what it looks like. 2dB or 3dB of
difference are not negligible, I wouldn't want there to be
intermodulation at the input, but then you should see replicas even
further away from the carrier.
Try to attenuate the input level a little: if the spurs decrease
non-linearly it is input intermodulation, otherwise they are spurious
from the NCO.
Claudio
The PLL synthesizer is the MAX2871, datasheet below:
https://www.analog.com/media/en/technical-documentation/data-sheets/max2871.pdf
The TX-side mixer is the ADL5375, datasheet below:
https://www.analog.com/media/en/technical-documentation/data-sheets/ADL5375.pdf
These two components will dominate in terms of phase-noise and spur
performance.
You might try setting the synthesizer in integer-N mode, if your target
frequency is amenable to integer_n tuning:
https://files.ettus.com/manual/structuhd_1_1tune__request__t.html
*From:* discuss-gnuradio-bounces+claudio.franchini=tlrnet...@gnu.org
<discuss-gnuradio-bounces+claudio.franchini=tlrnet...@gnu.org> *On
Behalf Of *Dor Ratz
*Sent:* Tuesday, February 21, 2023 12:41 PM
*To:* discuss-gnuradio@gnu.org
*Subject:* Spurs in UBX-160 Daughterboard with USRP X310
Hello,
I have some problems with spurs in ubx-160 daughterboard with USRP
X310. Interesting thing.
I transmit in Gnuradio simple signal source of cosine wave in
frequency 1003MHz with Gain=15dB and connect the USRP to spectrum
analyzer.
I can see the signal in 1003MHz in +8dBm as expected, but why do I see
spur in 1003.006MHz (6KHz offset) at amplitude of (-40dBc) relative to
the transmitted signal?
It can be seen when with small enough RBW and span values in the
spectrum analyzer.
As far I understand from ubx 160 daughterboard RF information spec,
the phase noise should be (-90dBc/Hz) -(-100dBc/Hz) and not that high
as I get.
I don't know if my spur source is phase noise or some other spectral
issue.
I'm well below the values of Tx max power and TX OIP3 of ubx-160.
Thanks a lot for any advice.