# Gnuradio FFT - Graph concatenation **URL:** \ **Category:** GNU Radio\ **Created:** [June 11, 2015, 4:00pm UTC](https://www.ruby-forum.com/t/gnuradio-fft-graph-concatenation/242280 "2015-06-11T16:00:58Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [June 11, 2015, 4:00pm UTC](https://www.ruby-forum.com/t/gnuradio-fft-graph-concatenation/242280/1 "2015-06-11T16:00:58Z")
Hi, I’m using USRP E310 and running uhd\_fft.grc to acquire FFT spectrum from the device in network mode, and then displays that with QT FFT GUI block. Setting a center frequency, I can get an instantaneous bandwidth of 32MHz around the center frequency. (for me it’s the maximum in network mode) Now, I want to change the center frequency programmatically in order to sweep a larger bandwidth and then concatenate the results into a single QT FFT graph like this: -IQ/2-----Cent.freq1-----+IQ/2 -IQ/2-----Cent.freq2------+IQ/2 -IQ/2-----Cent.freq2------+IQ/2 … Is their a way I can do it? Regards, ---
**Author:** ![Hassaan\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/779978/32.png) [@Hassaan\_A](https://www.ruby-forum.com/u/Hassaan_A)\ **Post date:** [June 11, 2015, 4:10pm UTC](https://www.ruby-forum.com/t/gnuradio-fft-graph-concatenation/242280/2 "2015-06-11T16:10:19Z")
On Thu, Jun 11, 2015 at 9:59 AM, Hassaan A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > -IQ/2-----Cent.freq1-----+IQ/2 -IQ/2-----Cent.freq2------+IQ/2 > -IQ/2-----Cent.freq2------+IQ/2 … > > Is their a way I can do it? > > Regards, The QTGUI FFT sink has a message port that allows you to control the center frequency. See the Detailed Description here > **[GNU Radio Manual and C++ API Reference: gr::qtgui::freq\_sink\_c Class Reference](https://www.gnuradio.org/doc/doxygen/classgr_1_1qtgui_1_1freq __sink__ c.html)** Tom ---
**Author:** ![Hassaan\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/779978/32.png) [@Hassaan\_A](https://www.ruby-forum.com/u/Hassaan_A)\ **Post date:** [June 11, 2015, 4:27pm UTC](https://www.ruby-forum.com/t/gnuradio-fft-graph-concatenation/242280/3 "2015-06-11T16:27:16Z")
Thanks for the guidance. Can I do this message passing in GRC? Also, how would the bandwidths get concatenated together and displayed in the same FFT graph? ---
**Author:** ![Hassaan\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/779978/32.png) [@Hassaan\_A](https://www.ruby-forum.com/u/Hassaan_A)\ **Post date:** [June 11, 2015, 4:40pm UTC](https://www.ruby-forum.com/t/gnuradio-fft-graph-concatenation/242280/4 "2015-06-11T16:40:07Z")
On Thu, Jun 11, 2015 at 10:25 AM, Hassaan A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Thanks for the guidance. > > Can I do this message passing in GRC? Also, how would the bandwidths get > concatenated together and displayed in the same FFT graph? Check out our tutorials on [gnuradio.org](http://gnuradio.org) for message passing help. In the FFT blocks, go into the Properties and in the General tab at the bottom there’s a “Show Msg Ports” option that you’ll need to turn on. You wouldn’t be able to concatenate the signals in the plot. The plots are designed for real-time use, so each time plots, it’s based on the newest signal information in the data stream. So the old stuff would be gone. The message port just changes the center frequency with the same bandwidth. What you want is very specialized, so you’ll probably have to write something of your own for this. Tom ---
**Author:** ![Hassaan\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/779978/32.png) [@Hassaan\_A](https://www.ruby-forum.com/u/Hassaan_A)\ **Post date:** [June 11, 2015, 4:52pm UTC](https://www.ruby-forum.com/t/gnuradio-fft-graph-concatenation/242280/5 "2015-06-11T16:52:24Z")
> What you want is very specialized, so you’ll probably have to write > something of your own for this. > > Tom I want to amplify on this point. The number of “useful things” you might want to do with a real-time sample-stream in the context of DSP and radio is very, very large, nearly infinite, and that “near infinity” expands as we learn to do more useful things (because of the standing-on-the-shoulders-of-giants effect). So, having a finite frame (Gnu Radio) and expecting it to, out-of-the-box, address any _particular_ aspect of that near-infinite-sea of possibilities is unrealistic. Using a “proximate analogy”. When you encounter the C++ compiler for the first time, you may notice that it doesn’t, “out of the box” automatically know how to implement a spreadsheet, or a database, or any particular item in the infinite-sea of applications you could write in C++. Gnu Radio is the same. It’s a toolbox. A very rich toolbox, but a toolbox, nonetheless. There’s no magic “make my answers come out” button. When one is working in one small corner of “wireless” or “DSP” or “RF systems”, it is often tempting to think that your particular corner, whatever it is, constitutes “the biggest class of application”, and expect the tooling to be “born knowing” how to deal with your particular class of application. It just isn’t realistic. This is a general comment, not directed any anyone in particular, and one that I’ve made in the past, and will probably make again from time to time. ---
**Author:** ![Hassaan\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/779978/32.png) [@Hassaan\_A](https://www.ruby-forum.com/u/Hassaan_A)\ **Post date:** [June 11, 2015, 5:46pm UTC](https://www.ruby-forum.com/t/gnuradio-fft-graph-concatenation/242280/6 "2015-06-11T17:46:43Z")
On Jun 11, 2015, at 6:59, Hassaan A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I’m using USRP E310 and running uhd\_fft.grc to acquire FFT spectrum from the > device in network mode, and then displays that with QT FFT GUI block. > > Setting a center frequency, I can get an instantaneous bandwidth of 32MHz around > the center frequency. (for me it’s the maximum in network mode) Now, I want to > change the center frequency programmatically in order to sweep a larger bandwidth > and then concatenate the results into a single QT FFT graph like this: Balint S. posted a video on May 30 demonstrating doing exactly this (with a USRP X310; I don’t know if the capabilities are different enough to matter). [![](https://img.youtube.com/vi/w9wlKYDEOUU/maxresdefault.jpg "SDR Wideband Spectrum Monitoring for Drone FPV Frequency Management") ](https://www.youtube.com/watch?v=w9wlKYDEOUU) SDR Wideband Spectrum Monitoring for Drone FPV Frequency Management At 2:00 “I just prototyped a GNU Radio block yesterday…” Perhaps he should be encouraged to move it beyond prototype status! – Kevin R. [http://switchb.org/kpreid/](http://switchb.org/kpreid/) ---
**Author:** ![Hassaan\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/779978/32.png) [@Hassaan\_A](https://www.ruby-forum.com/u/Hassaan_A)\ **Post date:** [June 11, 2015, 11:43pm UTC](https://www.ruby-forum.com/t/gnuradio-fft-graph-concatenation/242280/7 "2015-06-11T23:43:40Z")
Hello Hassaan, there’s no way you get 32MHz of bandwidth over network mode – for 16 bit samples, that’s not even theoretically possible over gigabit ethernet. In fact, the E310’s CPU will under no circumstances push that many samples per second in or out of the E310. Please make sure you actually get the bandwidth you think you are getting. I’d like to point out that the network mode really is a narrowband diagnostic and maybe demo tool, but can’t be used for serious sample rates – the architecture of the network interface on the E310 just doesn’t allow such rates when handled by the ARM. Best regards, Marcus