Re: [Discuss-gnuradio] Creating a FFT plot like the one in this youtube variable

[Marcus Müller]

Hi Ashraf,

I don't want to complain much, but this feels like you're only giving us fractions of the information that is easily available to you, but expect us to guess what you're seeing; try to understand the situation of someone who's trying to understand your problems:

now you've just sent us two uncommented screenshots, and we don't know what situation you're actually showing -- is it what you see when there's no signal? Is it what you see when there is signal? How do these spectra look in comparison? Also, you haven't explained anything about what you're transmitting, with which bandwidth, using which devices, antennas, gains/powers etc.

The only thing that I can say for sure is that you're misunderstanding the "bandwidth" parameter of the graphical sink: Of course, the sink always displays the bandwidth of the sampled signal you send into it -- which, for complex signals, is the sampling rate, and the bandwidth parameter just puts the numbers on the axis. The actual bandwidth you're observing is 100kHz, not 2MHz! you need to modify the sampling rate if you want to change that.

I remember we had a discussion on whether any GNU Radio sink actually displays powers (in dBm) or just relative values (dB); this is exactly the same! Frequency is displayed relative to the bandwidth you set in the sink parameters -- it's not a quality inherent to the sequence of numbers that is your digital signal.

Best regards,
Marcus

On 22.07.2015 19:32, Ashraf Younis wrote:

On Wed, Jul 22, 2015 at 12:01 PM, Marcus Müller <address@hidden> wrote:

Hi Ashraf,

If you've configured the USRP source correctly, you're very likely actually displaying the spectrum your digital receiver sees -- depending on the signal, you could a) actually be rising the power level in that whole band, or b) maybe you're observing something like saturation and hence intermodulation of additional signals.

You migth want to share what exactly you are observing, and what exactly the signal is you're generating. Screenshots are easy to make and to upload [1], so please illustrate a little better!

Best regards,
Marcus


[1] www.imgur.com

On 22.07.2015 17:56, Ashraf Younis wrote:

Hello, the issue I am having is I cannot display a graph that shows a wide range of frequencies and their power. When I attempt it with the QT GUI Frequency in GRC, I get something similar to the one in this video (FFT plot) but then I transmit a signal in the range I am currently looking at and the whole line moves up. This leads me to believe that I am no displaying the whole range I desire, but in fact I am displaying the center frequency and a small bandwidth around it. I want to, for example, scan the 2.4 GHz range and see all of the channels and their power. And when I transmit at a certain frequency, I see a spike at the spot in the graph.

How do I create that graph?

_______________________________________________
Discuss-gnuradio mailing list
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

_______________________________________________
Discuss-gnuradio mailing list
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio