Hello, I observe a spurious signal in the PSD estimates that are obtained using a USRP, which I cannot identify the cause. Could someone help me identifying the cause of this? Plots are shown below. *Hardware*: -USRP N200 r4 + UBX-40 v1 -Agilent FieldFox SA, as the reference. *Software*: -Windows Server 2012 -UHD 3.9.3 -GNURadio 3.7.10.1 ..and also on a UHD-based (non-GNU Radio) spectrum scanner script that I am working on. *Setting*: Gain : 0 lo offset : 0 Samp rate : 25MS/s (100e6/4) Antenna: RX2 *The Spurious Signal:* @ fc = 641.25 MHz (reproducible at 642 / 641 MHz) ​ Goes away @ fc = 630MHz. ​ *+- 25MHz*: No, I don't see any signal that could get aliased; I believe this is not due to the aliasing from the DDC. ​ *1/2 fc (315MHz):* Clean (no signal observed). ​ Regards, Kyeong Su Shin

Hello Kyeong Su Shin, what's the RF power reaching the USRP? Does this get better when you reduce the RX gain or the TX power? Best regards, Marcus On 26.07.2017 16:52, Kyeong Su Shin via USRP-users wrote: > Hello, > > I observe a spurious signal in the PSD estimates that are obtained > using a USRP, which I cannot identify the cause. Could someone help me > identifying the cause of this? > > Plots are shown below. > > _Hardware_: > -USRP N200 r4 + UBX-40 v1 > -Agilent FieldFox SA, as the reference. > > _Software_: > -Windows Server 2012 > -UHD 3.9.3 > -GNURadio 3.7.10.1 > > ..and also on a UHD-based (non-GNU Radio) spectrum scanner script that > I am working on. > > _Setting_: > Gain : 0 > lo offset : 0 > Samp rate : 25MS/s (100e6/4) > Antenna: RX2 > > _The Spurious Signal:_ > > @ fc = 641.25 MHz (reproducible at 642 / 641 MHz) > > ​ > Goes away @ fc = 630MHz. > > ​ > _+- 25MHz_:_ > > _No, I don't see any signal that could get aliased; I believe this is > not due to the aliasing from the DDC._ > > _ > > > ​ > _1/2 fc (315MHz):_ Clean (no signal observed). > > > ​ > > Regards, > Kyeong Su Shin > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

Hello Marcus Müller, I have no control to the TX power, as it is attached to an outdoor discone antenna (sorry, I forgot to mention that). I am cross-checking the measured spectrum against an Aglient spectrum analyzer. I am also using 0dB RX gain now, although maybe I can go and attach more attenuators to achieve lower gain levels. I tried increasing the RX gain (instead of decreasing it), and the relationship was apparently linearly dependent. (5dB increase in gain -> approx. 5dB increase in the power level in dBFS, 10dB increase in gain -> approx. 11dB increase in the power level in dBFS). The LNA got seriously overloaded when I tried 15dB RX gain (noise increase). The strength of the spurious signal was quickly varying, so I could have had mismeasured it, though. Attached is the PSD estimates collected using a Agilent SA (somewhat coarse version). Regards, Kyeong Su Shin On Wed, Jul 26, 2017 at 1:07 PM, Marcus Müller via USRP-users < usrp-users@lists.ettus.com> wrote: > Hello Kyeong Su Shin, > > what's the RF power reaching the USRP? Does this get better when you > reduce the RX gain or the TX power? > > Best regards, > > Marcus > > On 26.07.2017 16:52, Kyeong Su Shin via USRP-users wrote: > > Hello, > > I observe a spurious signal in the PSD estimates that are obtained using a > USRP, which I cannot identify the cause. Could someone help me identifying > the cause of this? > > Plots are shown below. > > *Hardware*: > -USRP N200 r4 + UBX-40 v1 > -Agilent FieldFox SA, as the reference. > > *Software*: > -Windows Server 2012 > -UHD 3.9.3 > -GNURadio 3.7.10.1 > > ..and also on a UHD-based (non-GNU Radio) spectrum scanner script that I > am working on. > > *Setting*: > Gain : 0 > lo offset : 0 > Samp rate : 25MS/s (100e6/4) > Antenna: RX2 > > *The Spurious Signal:* > > @ fc = 641.25 MHz (reproducible at 642 / 641 MHz) > > ​ > Goes away @ fc = 630MHz. > > ​ > *+- 25MHz*: > > No, I don't see any signal that could get aliased; I believe this is not > due to the aliasing from the DDC. > > > > ​ > *1/2 fc (315MHz):* Clean (no signal observed). > > > ​ > > Regards, > Kyeong Su Shin > > > _______________________________________________ > USRP-users mailing listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >

 Hello Kyeong Su Shin,

 what's the RF power reaching the USRP? Does this get better when
 you reduce the RX gain or the TX power?

 Best regards,

 Marcus


 On 26.07.2017 16:52, Kyeong Su Shin via USRP-users wrote:

 Hello,

 I observe a spurious signal in the PSD estimates that are
 obtained using a USRP, which I cannot identify the cause. Could
 someone help me identifying the cause of this?

 Plots are shown below.

 _Hardware_:
 -USRP N200 r4 + UBX-40 v1
 -Agilent FieldFox SA, as the reference.

 _Software_:
 -Windows Server 2012
 -UHD 3.9.3
 -GNURadio 3.7.10.1

 ..and also on a UHD-based (non-GNU Radio) spectrum scanner script
 that I am working on.

 _Setting_:
 Gain : 0
 lo offset : 0
 Samp rate : 25MS/s (100e6/4)
 Antenna: RX2

 _The Spurious Signal:_

 @ fc = 641.25 MHz (reproducible at 642 / 641 MHz)

 ​
 Goes away @ fc = 630MHz.

 ​
 _+- 25MHz_:_

 _No, I don't see any signal that could get aliased; I believe
 this is not due to the aliasing from the DDC._

 _


 ​
 _1/2 fc (315MHz):_ Clean (no signal observed).


 ​

 Regards,
 Kyeong Su Shin


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 http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
 <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com>

 _______________________________________________ USRP-users mailing
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 <mailto:USRP-users@lists.ettus.com>
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Dear Kyeong Su Shin, so, when things already get "seriously overloaded" at 15dB gain, and you're running at 0 dB, I think the likeliest explanation is that at 0 dB, you're already seeing the effects of overloading. Try with something like 40 dB attenuation between antenna and LNA. Best regards, Marcus On 07/27/2017 09:41 AM, Kyeong Su Shin via USRP-users wrote: > Hello Marcus Müller, > > I have no control to the TX power, as it is attached to an outdoor > discone antenna (sorry, I forgot to mention that). I am cross-checking > the measured spectrum against an Aglient spectrum analyzer. I am also > using 0dB RX gain now, although maybe I can go and attach more > attenuators to achieve lower gain levels. > > I tried increasing the RX gain (instead of decreasing it), and the > relationship was apparently linearly dependent. (5dB increase in gain > -> approx. 5dB increase in the power level in dBFS, 10dB increase in > gain -> approx. 11dB increase in the power level in dBFS). The LNA got > seriously overloaded when I tried 15dB RX gain (noise increase). The > strength of the spurious signal was quickly varying, so I could have > had mismeasured it, though. > > Attached is the PSD estimates collected using a Agilent SA (somewhat > coarse version). > > Regards, > Kyeong Su Shin > > On Wed, Jul 26, 2017 at 1:07 PM, Marcus Müller via USRP-users > <usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>> wrote: > > Hello Kyeong Su Shin, > > what's the RF power reaching the USRP? Does this get better when > you reduce the RX gain or the TX power? > > Best regards, > > Marcus > > > On 26.07.2017 16:52, Kyeong Su Shin via USRP-users wrote: >> Hello, >> >> I observe a spurious signal in the PSD estimates that are >> obtained using a USRP, which I cannot identify the cause. Could >> someone help me identifying the cause of this? >> >> Plots are shown below. >> >> _Hardware_: >> -USRP N200 r4 + UBX-40 v1 >> -Agilent FieldFox SA, as the reference. >> >> _Software_: >> -Windows Server 2012 >> -UHD 3.9.3 >> -GNURadio 3.7.10.1 >> >> ..and also on a UHD-based (non-GNU Radio) spectrum scanner script >> that I am working on. >> >> _Setting_: >> Gain : 0 >> lo offset : 0 >> Samp rate : 25MS/s (100e6/4) >> Antenna: RX2 >> >> _The Spurious Signal:_ >> >> @ fc = 641.25 MHz (reproducible at 642 / 641 MHz) >> >> ​ >> Goes away @ fc = 630MHz. >> >> ​ >> _+- 25MHz_:_ >> >> _No, I don't see any signal that could get aliased; I believe >> this is not due to the aliasing from the DDC._ >> >> _ >> >> >> ​ >> _1/2 fc (315MHz):_ Clean (no signal observed). >> >> >> ​ >> >> Regards, >> Kyeong Su Shin >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com> >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com> > _______________________________________________ USRP-users mailing > list USRP-users@lists.ettus.com > <mailto:USRP-users@lists.ettus.com> > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com> > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

Hello Marcus Müller, Thank you, I will give it a shot. Regards, Kyeong Su Shin On Thu, Jul 27, 2017 at 6:34 AM, Marcus Müller via USRP-users < usrp-users@lists.ettus.com> wrote: > Dear Kyeong Su Shin, > > so, when things already get "seriously overloaded" at 15dB gain, and > you're running at 0 dB, I think the likeliest explanation is that at 0 dB, > you're already seeing the effects of overloading. Try with something like > 40 dB attenuation between antenna and LNA. > > Best regards, > > Marcus > > On 07/27/2017 09:41 AM, Kyeong Su Shin via USRP-users wrote: > > Hello Marcus Müller, > > I have no control to the TX power, as it is attached to an outdoor discone > antenna (sorry, I forgot to mention that). I am cross-checking the measured > spectrum against an Aglient spectrum analyzer. I am also using 0dB RX gain > now, although maybe I can go and attach more attenuators to achieve lower > gain levels. > > I tried increasing the RX gain (instead of decreasing it), and the > relationship was apparently linearly dependent. (5dB increase in gain -> > approx. 5dB increase in the power level in dBFS, 10dB increase in gain -> > approx. 11dB increase in the power level in dBFS). The LNA got seriously > overloaded when I tried 15dB RX gain (noise increase). The strength of the > spurious signal was quickly varying, so I could have had mismeasured it, > though. > > Attached is the PSD estimates collected using a Agilent SA (somewhat > coarse version). > > Regards, > Kyeong Su Shin > > On Wed, Jul 26, 2017 at 1:07 PM, Marcus Müller via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> Hello Kyeong Su Shin, >> >> what's the RF power reaching the USRP? Does this get better when you >> reduce the RX gain or the TX power? >> >> Best regards, >> >> Marcus >> >> On 26.07.2017 16:52, Kyeong Su Shin via USRP-users wrote: >> >> Hello, >> >> I observe a spurious signal in the PSD estimates that are obtained using >> a USRP, which I cannot identify the cause. Could someone help me >> identifying the cause of this? >> >> Plots are shown below. >> >> *Hardware*: >> -USRP N200 r4 + UBX-40 v1 >> -Agilent FieldFox SA, as the reference. >> >> *Software*: >> -Windows Server 2012 >> -UHD 3.9.3 >> -GNURadio 3.7.10.1 >> >> ..and also on a UHD-based (non-GNU Radio) spectrum scanner script that I >> am working on. >> >> *Setting*: >> Gain : 0 >> lo offset : 0 >> Samp rate : 25MS/s (100e6/4) >> Antenna: RX2 >> >> *The Spurious Signal:* >> >> @ fc = 641.25 MHz (reproducible at 642 / 641 MHz) >> >> ​ >> Goes away @ fc = 630MHz. >> >> ​ >> *+- 25MHz*: >> >> No, I don't see any signal that could get aliased; I believe this is not >> due to the aliasing from the DDC. >> >> >> >> ​ >> *1/2 fc (315MHz):* Clean (no signal observed). >> >> >> ​ >> >> Regards, >> Kyeong Su Shin >> >> >> _______________________________________________ >> USRP-users mailing listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> _______________________________________________ USRP-users mailing list >> USRP-users@lists.ettus.com http://lists.ettus.com/mailman >> /listinfo/usrp-users_lists.ettus.com > > _______________________________________________ > USRP-users mailing listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >