Re: Spurs in UBX-160 Daughterboard with USRP X310

[Dor Ratz]

Thanks a lot Marcus and Claudio, I'll check it and update if needed

Dor 

בתאריך יום ג׳, 21 בפבר׳ 2023, 4:48 אחה״צ, מאת Marcus D. Leech ‏<patchvonbraun@gmail.com>:

On 21/02/2023 08:43, claudio.franchini@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.eu@gnu.org <discuss-gnuradio-bounces+claudio.franchini=tlrnet.eu@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.