Re: [Discuss-gnuradio] USRP GNU radio receiver

Thank you very much!

This tip is very helpful.

Could you say some documents or web pages about setting the "FE Options"?

Best Regards,

Simona

Il giorno gio 18 lug 2019 alle ore 18:03 Nick Foster <bistromath@gmail.com> ha scritto:

The USRP has a DC offset removal filter in the FPGA. A carrier sent at 0Hz is exactly the same as DC offset, and will be removed. Zero-IF receiver architectures (like the USRP) intrinsically have DC offset imperfections. The filter can be disabled in the USRP Source "FE Options" tab. It is not good practice to design a system which depends on DC in a zero-IF receiver, because the DC offset error will change over frequency, temperature, time, etc.

On Thu, Jul 18, 2019 at 4:29 AM Simona Sibio <ssibio2@gmail.com> wrote:

Hi all,

Thank you very much for your emails.

But no tip works fine.

I wanted only to learn how is USRP working with GNU radio, I thought that the RX chain in the USRP was different.

But I am not the beginner in electronic and RF circuits.

Anyway, no problem, I don't ask more information about this.

Best Regards,

Simona

Il giorno gio 18 lug 2019 alle ore 12:11 Jonas Manthey <jonas.manthey@u-blox.com> ha scritto:

Hi,

 

You don't send a sine with  frequency 0, you send a carrier that is modulated by a sine with a frequency of 0. A sine with a frequency of 0 is 0: sin(2 pi f) = sin(2 pi 0) = sin(0) = 0.

 

So your carrier is modulated with a zero, which I *think* ends up in no carrier at all, not sure right now how zero-IF architectures behave in that case. I highly recommend reading some communications or RF book/website/guide or talk with your advisor.

 

UHD-USRP clips anything above 1 if left in the default setting (float I guess) and there will be a lot of garbage in the sent spectrum.

 

Cheers,

Jonas

 

From: Discuss-gnuradio [mailto:discuss-gnuradio-bounces+jonas.manthey=u-blox.com@gnu.org] On Behalf Of Simona Sibio
Sent: Donnerstag, 18. Juli 2019 13:01
To: Kyeong Su Shin <ksshin@postech.ac.kr>
Cc: discuss-gnuradio@gnu.org
Subject: Re: [Discuss-gnuradio] USRP GNU radio receiver

 

Hi Kyeong,

 

I attached the screenshots about time-domain and frequency domain.

I sent a sine with frequency=0 and amplitude=0,25.

The output is always zero in the receiver.

The situation changes only if I send a sine with a frequency non-zero.

Thank you for your time.

Best Regards,

 

Simona

 

Il giorno mer 17 lug 2019 alle ore 17:41 Kyeong Su Shin <ksshin@postech.ac.kr> ha scritto:

To whom it may concern:

 

I think there has been some miscommunications or misunderstandings here: the 'Offset' argument for the 'Signal Source' block is for the 'amplitude offset' of the signal, while what Marcus probably meant in his previous e-mail is the 'frequency offset' (you can use USRP's low-freq digital IF capabilities for that). Also, I do not know how UHD sink behaves when you do not input normalized values, but I am pretty sure that you should not input such large values to UHD sink.

 

If readings in the frequency-domain are non-zero (or, in real-world devices, extremely low values), readings in the time-domains are also non-zero. So, "the output became unstable in frequency and in time is always zero" doesn't make sense. Your time-domain plot is probably zoomed out too much.

 

Finally, as Marcus mentioned, throttle blocks _must_ be removed.

 

Regards,

Kyeong Su Shin

 

---

보낸 사람: Simona Sibio <ssibio2@gmail.com> 대신 Discuss-gnuradio <discuss-gnuradio-bounces+ksshin=postech.ac.kr@gnu.org>
보낸 날짜: 2019년 7월 17일 수요일 오후 11:35:00
받는 사람: Müller, Marcus (CEL)
참조: discuss-gnuradio@gnu.org
제목: Re: [Discuss-gnuradio] USRP GNU radio receiver

 

Thank you very much!

I sent the screenshot because in the oscilloscope there is not the offset.

Instead, I would like to detect that.

Thank you in advance.

 

Simona

 

Il giorno mer 17 lug 2019 alle ore 15:22 Müller, Marcus (CEL) <mueller@kit.edu> ha scritto:

1. Never use a throttle with a hardware block. GRC's log will actually
shout at you that you shouldn't be doing that!
2. I must admit this is about as good as I'd expect. I of course can't
infer temporal behaviour from screenshots.

Best regards,
Marcus

On Wed, 2019-07-17 at 14:18 +0100, Simona Sibio wrote:
> Hi Marcus,
>
> I tried to change the offset in the transmitter but the output in the receiver is the same, also if I send a sine signal with 10 Hz and 0,1 amplitude: the output became unstable in frequency and in time is always zero (see attached, 130K).
> The flow graph is attached.
> Do you have any suggestions?
> Thank you in advance.
>
> Simona
>
> Il giorno mar 16 lug 2019 alle ore 18:59 Müller, Marcus (CEL) <mueller@kit.edu> ha scritto:
> > That phase is not any more or less random than that of your local
> > oscillator, so there might be some misunderstanding here.
> > On Tue, 2019-07-16 at 18:52 +0100, Simona Sibio wrote:
> > > Thank you very much!
> > > But, with the offset tuning I cannot edit the phase.
> > > Maybe, I have to change method.
> > > Best Regards,
> > >
> > > Simona
> > >
> > > Il giorno mar 16 lug 2019 alle ore 18:25 Müller, Marcus (CEL) <mueller@kit.edu> ha scritto:
> > > > Well, there's leakage / DC blocking filters in most mixers, so yes.
> > > >
> > > > But the solution is simple (and hardware-supported transparently on
> > > > USRPs): Just tune at an offset, and mix down to 0 Hz (==constant!) in
> > > > digital. Your USRP can do that for you, google for "USRP offset
> > > > tuning".
> > > >
> > > > Best regards,
> > > > Marcus
> > > >
> > > > On Tue, 2019-07-16 at 18:15 +0100, Simona Sibio wrote:
> > > > > Thank you very much!!
> > > > > Then, I cannot measure a constant because, in the RX chain, maybe, some filter deletes the information, doesn't it?
> > > > > Thank you for your time and tour tips!
> > > > >
> > > > > Best Regards,
> > > > >
> > > > > Simona
> > > > >
> > > > > Il giorno mar 16 lug 2019 alle ore 18:01 Müller, Marcus (CEL) <mueller@kit.edu> ha scritto:
> > > > > > Look up what a quadrature modulator does. It's just a multiplication
> > > > > > with e^{j2\pi f_{carrier}t}, in the end.
> > > > > >
> > > > > > Your constant signal s(t) = c const. would hence be transmitted as
> > > > > >
> > > > > > c·e^{j2\pi f_{carrier}t}
> > > > > >
> > > > > > whereas a complex sinusoid of frequency f and amplitude a,
> > > > > > s(t) = a·e^{j2\pi f t) would be transmitted as
> > > > > >
> > > > > > a·e^{j2\pi f t)·e^{j2\pi f_{carrier}t} = a·e^{j2\pi (f+f_{carrier})t} 
> > > > > >
> > > > > > so, identical to the constant signal, just at a different frequency.
> > > > > >
> > > > > >
> > > > > > Best regards,
> > > > > > Marcus
> > > > > >
> > > > > > On Tue, 2019-07-16 at 17:53 +0100, Simona Sibio wrote:
> > > > > > > Hi Marcus,
> > > > > > >
> > > > > > > Thank you for tip!
> > > > > > > I know that calibration is not so easy but I hope that.
> > > > > > > Could you help me to understand what happened with a constant complex baseband signal?
> > > > > > > I am beginner in this field.
> > > > > > > Thank you for your time.
> > > > > > >
> > > > > > > Best Regards,
> > > > > > >
> > > > > > > Simona
> > > > > > >
> > > > > > > Il giorno mar 16 lug 2019 alle ore 17:39 Müller, Marcus (CEL) <mueller@kit.edu> ha scritto:
> > > > > > > > Watch out! What do you get at the *output* of your SDR device when you
> > > > > > > > transmit a constant complex baseband signal, mixed to a carrier
> > > > > > > > frequency? How does that differ from transmitting a complex baseband
> > > > > > > > sinusoid mixed to a carrier frequency?
> > > > > > > >
> > > > > > > > On Tue, 2019-07-16 at 18:32 +0200, sumit kumar wrote:
> > > > > > > > > Ok, so for a constant source, in the time domain you will see a flat signal only! Try connecting a spectrum analyzer and you shud see a peak at DC becz Fourier transform of constant signal is impulse.
> > > > > > > > > And yes, as Marcus said, increase the sampling rate!
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > On Tue, 16 Jul 2019 at 18:06, Simona Sibio <ssibio2@gmail.com> wrote:
> > > > > > > > > > Thank you for the assistance.
> > > > > > > > > >
> > > > > > > > > > I put the module "constant source" in my flow grap.
> > > > > > > > > > With this module, I can choose witch amplitude I want to send.
> > > > > > > > > > I attached the flow graph.
> > > > > > > > > > And, I would want to read these values in the receiver.
> > > > > > > > > >
> > > > > > > > > > Simona
> > > > > > > > > >
> > > > > > > > > > Il giorno mar 16 lug 2019 alle ore 16:58 sumit kumar <sumitstop@gmail.com> ha scritto:
> > > > > > > > > > > Hi Simona, what is the "constant signal" here ?
> > > > > > > > > > >
> > > > > > > > > > > On Tue, 16 Jul 2019 at 17:54, Simona Sibio <ssibio2@gmail.com> wrote:
> > > > > > > > > > > > Hi all,
> > > > > > > > > > > >
> > > > > > > > > > > > I want to use GNU radio to measure the amplitude and the phase of a signal.
> > > > > > > > > > > > I send a constant signal with the transmitter USRP but in the receiver there is a flat signal with amplitude 0 and offset 0.
> > > > > > > > > > > > I tried to send a sine signal and the receveir works fine.
> > > > > > > > > > > > How can I do to send only a constant and measure the amplitude?
> > > > > > > > > > > >
> > > > > > > > > > > > Thank you for your time.
> > > > > > > > > > > >
> > > > > > > > > > > > Simona
> > > > > > > > > > > >
> > > > > > > > > > > > _______________________________________________
> > > > > > > > > > > > Discuss-gnuradio mailing list
> > > > > > > > > > > > Discuss-gnuradio@gnu.org
> > > > > > > > > > > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > --
> > > > > > > > > > > Sumit Kumar
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > _______________________________________________
> > > > > > > > > Discuss-gnuradio mailing list
> > > > > > > > > Discuss-gnuradio@gnu.org
> > > > > > > > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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