# WX GUI FFT sink block issues **URL:** \ **Category:** GNU Radio\ **Created:** [April 23, 2014, 9:06am UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611 "2014-04-23T09:06:11Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\ **Post date:** [April 23, 2014, 9:06am UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/1 "2014-04-23T09:06:11Z")
I am facing issues regarding WX GUI fft sink block… First that whatever center frequency i am providing it is showing a peak at that frequency whether input signal is there or not…?? Secondly there is a question that whether it can automatically shift to the frequency by detecting the frequency of the input signal or not?? Another issue in general that i am unable to use two sink blocks at the same time…e.g.if i am using fft sink and scope sink then when i execute it(i have no hardware attached uptill now)…then both plots are empty and i have to disable one of them to get working…?? any help would be appreciated…thnx in advance ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 23, 2014, 1:08pm UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/2 "2014-04-23T13:08:04Z")
On Wed, 23 Apr 2014 12:04:52 +0500 ali hanif [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I am facing issues regarding WX GUI fft sink block.. > First that whatever center frequency i am providing it is showing a peak at > that frequency whether input signal is there or not..?? The peak means that there is a DC bias component in your signal. That’s pretty normal, depending on what kind of hardware you use. E.g. a bladeRF will show it, while (at least some) RTL-SDR don’t have it. > Secondly there is a question that whether it can automatically shift to the > frequency by detecting the frequency of the input signal or not?? You can supply the center frequency to the block. You can specify it as a variable to all blocks that need it, in order to have it to change only at one place. > Another issue in general that i am unable to use two sink blocks at the > same time..e.g.if i am using fft sink and scope sink then when i execute > it(i have no hardware attached uptill now)..then both plots are empty and i > have to disable one of them to get working..?? That sounds weird. Can you show a screenshot of your GRC graph? (unless you are using a coded flow graph, than that please). ``` Attila K. ``` – The trouble with you, Shev, is you don’t say anything until you’ve saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap – Tirin, The Dispossessed, U. Le Guin ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 23, 2014, 2:53pm UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/3 "2014-04-23T14:53:42Z")
Hi! Just a side note: Try to replace your WX GUI widgets with QT ones (also set the Generate Option to QT in GRC). They are pretty mature and work well; also, in the long run, GNU Radio’s going to move away from WX. Greetings, Marcus ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 23, 2014, 4:27pm UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/4 "2014-04-23T16:27:00Z")
hi, I tried using QT GUI sink to measure frequency offset between 2 USRPs.but when I click “Execute the flow graph”,a window appears then in a blink disappears.and i got this massage.did I set something wrong? Generating: “/home/sdr/top\_block.py” Executing: “/home/sdr/top\_block.py” linux; GNU C++ version 4.6.3; Boost\_104800; UHD\_003.007.000-1-stable – Opening a USRP2/N-Series device… – Current recv frame size: 1472 bytes – Current send frame size: 1472 bytes – Opening a USRP2/N-Series device… – Current recv frame size: 1472 bytes – Current send frame size: 1472 bytes Using Volk machine: sse4\_1\_32 > > > Done – View this message in context: [http://gnuradio.4.n7.nabble.com/WX-GUI-FFT-sink-block-issues-tp47709p47721.html](http://gnuradio.4.n7.nabble.com/WX-GUI-FFT-sink-block-issues-tp47709p47721.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 23, 2014, 4:38pm UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/5 "2014-04-23T16:38:13Z")
im pretty sure I did that.i set Generate Options as QT GUI. if I didnt set Generate Options i will get this error: Generating: “/home/sdr/top\_block.py” Executing: “/home/sdr/top\_block.py” Traceback (most recent call last): File “/home/sdr/top\_block.py”, line 118, in tb = top\_block() File “/home/sdr/top\_block.py”, line 40, in **init** self.\_variable\_qtgui\_range\_0\_tool\_bar = Qt.QToolBar(self) TypeError: arguments did not match any overloaded call: QToolBar(QString, QWidget parent=None): argument 1 has unexpected type ‘top\_block’ QToolBar(QWidget parent=None): argument 1 has unexpected type ‘top\_block’ > > > Done – View this message in context: [http://gnuradio.4.n7.nabble.com/WX-GUI-FFT-sink-block-issues-tp47709p47723.html](http://gnuradio.4.n7.nabble.com/WX-GUI-FFT-sink-block-issues-tp47709p47723.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 24, 2014, 5:37am UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/6 "2014-04-24T05:37:06Z")
Hi Attila K., I don,t think it is the DC bias…as it is appearing at every center frequency i provide and a DC bias is at zero frequency only… ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 23, 2014, 4:29pm UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/7 "2014-04-23T16:29:58Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Strange… Are you sure you set the Generate Options to QT GUI (instead of WX)? Greetings, Marcus On 23.04.2014 16:25, sunkel wrote: > UHD\_003.007.000-1-stable > > – View this message in context: > [http://gnuradio.4.n7.nabble.com/WX-GUI-FFT-sink-block-issues-tp47709p47721.html](http://gnuradio.4.n7.nabble.com/WX-GUI-FFT-sink-block-issues-tp47709p47721.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Discuss-gnuradio > mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - [http://www.enigmail.net/](http://www.enigmail.net/) iQEcBAEBAgAGBQJTV84RAAoJEBQ6EdjyzlHtf/YH/2iUSzGe/N4TwkX+bzXqbRSo jEGCYkp3lZ/XxK1QCHJo4XP9dqXrV7FMW5WkOFW+PAozL3l5nyKNAXasRBwWTeCa EC76F1+75KqzaHI8orQHmPxIC2Q9RKp0Syyr3NtcQC/aXm1X8HTmb+XM/Ynj8htt c4DqW7roEEQZodM/5LZ3rZFamc8CdQEd8ygL29TTAbvb6+uCdUbj1gbHPqDShkQY ZGvpa3Ssmq+qxrzqALxUVAn/y+uYRM3RDAsHF9xmG0qIY3hnOjRZ9ogVks/Cqz6t eH6G91Cghr2DgAak/bx0oEIBVAA46BQCBivdGhWfEW50Ue3p6J+1gQ3afaCgSAQ= =rltD -----END PGP SIGNATURE----- ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 24, 2014, 6:35am UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/8 "2014-04-24T06:35:30Z")
For the last question,i have added a screen shot…see that there is no signal in my time plot,just a line… ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 24, 2014, 6:39am UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/9 "2014-04-24T06:39:03Z")
here is the GRC flow graph ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [May 1, 2016, 8:51pm UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/10 "2016-05-01T20:51:25Z")
Taking the advantage of this wx gui fft sink block issue, i just want to know about one problem i came across i.e. how can i get +ve amplitude values of the fft spectrum(signal amplitude)? The values i got were always -ve (the spectrum is shown below the 0 db amplitude). This question might had been discussed earlier but I am new in GNU radio. Anyone plz suggest me what cab be the solution. regards pitter ---
**Author:** ![ali\_hanif](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac91a4/32.png) [@ali\_hanif](https://www.ruby-forum.com/u/ali_hanif)\ **Post date:** [April 24, 2014, 9:34am UTC](https://www.ruby-forum.com/t/wx-gui-fft-sink-block-issues/240611/11 "2014-04-24T09:34:15Z")
Wow, it’s amazing that that flowgraph even works at all. 4.8 Gsps is an astronomical sample rate and shows a basic misunderstanding of how GnuRadio and SDR work. GnuRadio is a baseband processing architecture. Your SDR hardware (USRP, bladeRF, hackRF, etc.) is responsible for translating the baseband to a radio frequency, not GnuRadio. I’ve attached a more reasonable flowgraph for you to experiment with. Try some different parameters in the signal source and note the effects. You can download the flowgraph here: [http://www.w6rz.net/signal.grc](http://www.w6rz.net/signal.grc) Ron