FFT Audio

[Ben Chappell]

Hi,

I am hoping this is a GQRX question and not a Pi question.

Working on a 433MHz analogue scanner. Similar in concept to a falconry directional scanner. The tag is a double-pulsed tone. My first draft used an arduino, analogue 433 reciever and a buzzer. Sadly my potentiometer as an attenuator (for sensitivity adjustment) didn't work very well at all, even with a big yagi. So, I went down the pi route and upgraded from high-low input to the whole lot. GQRX is by far the best program i've tried. At 434.297, i have a pitch-perfect tone, no other noise. the display is very useful for corroborating the sound change as you get closer and start adjusting sensitivity. And looks great. Looking forward to a graphical display on the handheld, rather than an LED bar. I am new to the world of pi, but it's incredible.

The issue that i keep finding is that while happy with just a graphical display, the program stops a few seconds after turning on the sound (1s - several minutes later). The console simply repeats 'No FFT Audio'.

It's happy with fm so it may be that the 30% duty cycle of the signal is causing the issue. Would silence cause this program to stop? Has anyone else had this happen?

Using:

NESDR (nooelec.com) (based on RTL2832)

SMA 433 Ant.

RaspberryPi 3

Already tried (same result each time):

Jessie Lite, Ubuntu Mate, Rasbian images

The -r option when running GQRX, as admin

Power NESDR through a separately powered 2A USB hub

Reducing sample and baud rates as low as i can

All sound demod options (USB best)

Any advice on this would be great, or point me i the right direction if i'm posting in the wrong place, many thanks.

Ben.

*as an aside, feel free to disregard, does anyone know of an off the shelf USB UPS?

[Alexandru Csete]

Hi Ben,

If gqrx stops working and also the spectrum display stops, then it is
probably because the rtlsdr device stops working. On the Raspberry Pi
it could be because the power supply is not sufficient to power both
the raspberry pi and the devices you have attached to it.

Normally, you can see an error message in the terminal when this
happens. It should come before you start getting the "No audio FFT"
messages.

Alex

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[Ben Chappell]

Hi Alex,

Thanks for the reply. I agree. There is a colourful square when power low and i have seen it with GQRX running. So I tried a separate USB hub for the NESDR (2A) and a 2A supply for the Pi. I even disconnected the mouse and ethernet. Will keep trying. Good to narrow it down to the power. Will test the plugs.

Missed the error but will look out for it.

Ben.

[Ben Chappell]

#Hi Alex, here are the error messages as root after clean install (separate 2.5A available for both pi and usb hub):

(gqrx:2554): Gtk-WARNING **: Attempting to store changes into `/root/.local/share/recently-used.xbel', but failed: Failed to create file '/root/.local/share/recently-used.xbel.FZ65VY': No such file or directory

(gqrx:2554): Gtk-WARNING **: Attempting to set the permissions of `/root/.local/share/recently-used.xbel', but failed: No such file or directory
New FFT rate: 10 Hz
New FFT rate: 10 Hz
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

[Alexandru Csete]

Ben,

How do you install gqrx?
Also, please don't run gqrx as root.

Alex

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[Ben Chappell]

#Lastly, there are quite a few times without any error before the 'no fft audio':

Required number of taps: 215
New filter offset: -226000 Hz
setFftRate to "60 fps"
New FFT rate: 60 Hz
New FFT rate: 60 Hz
setFftSize to "16384"
New FFT rate: 60 Hz
New FFT rate: 60 Hz
New FFT rate: 60 Hz

No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.
No audio FFT data.

No audio FFT data.
OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

Thanks again.

[Ben Chappell]

Hi Alex,

Install by:

Sudo apt get install....

Ok, won't run as root. Does seem to last longer like this.

Ben.

[Alexandru Csete]

Ben,

The packages from the official repositories do not work on the
raspberry pi. Please uninstall, or start with a new SD card, and
follow the instructions here:
http://gqrx.dk/download/gqrx-sdr-for-the-raspberry-pi

Alex

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[Ben Chappell]

Hi Alex,

Will do! I tried it, but i've tried so many things, i'll start over and do it just that way. Thanks. 

Ben.