WX GUI FFT sink block issues


#1

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


#2

On Wed, 23 Apr 2014 12:04:52 +0500
ali hanif 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


#3

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


#4

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


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#5

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:
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#6

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…


#7

-----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:
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Sent from the GnuRadio mailing list archive at Nabble.com.

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#8

For the last question,i have added a screen shot…see that there is no
signal in my time plot,just a line…


#9

here is the GRC flow graph


#10

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


#11

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

Ron