FSK receiver

Dear all,

I have just built a FSK receiver aim to receive Cubesat data with FSK
modulation with 9600 baud rate, below is my flow graph.
I have just tested it with usb dongle RTL-SDR, however when I’m using
sink, I received OOOOO (overrun I think) continuously .
Does it have anything wrong with my set up ?

samplerate 2M
cut off freq 9600
transition 4800

I really appriciate for any comment on my FSK receiver flowgraph, I am a
newbie :slight_smile:

Thank you and best regard,

Hi Hoang,

Yes it’s a problem with your design. You have 2 Msps feeding into an
sink that probably goes up to 48 ksps. You need to change your sample
from 2 Msps to a rate your sound card supports. I would target one of
default rates you can select from the audio sink. You can use polyphase
arbitrary resampler block with the proper resampling ratio 2M/48k
leaving the taps blank and the other parameters to default.

Hope that helps,

On Fri, Aug 28, 2015 at 2:19 PM, Hoang Nguyen T. [email protected]

Thank you Rich,
I have added Rational Resample with the formular : Fs_out = Fs_in x
Interpolation / Decimation
Then the grc run without error.

On Fri, Aug 28, 2015 at 7:03 PM, Richard B. [email protected]

Hi Rich,
I am continue with the transmitting part ?
However, I cannot fine the FSK modulate block or Quadrature mod in GNU
radio companion.
Is there another block that use for FSK modulation in GNU radio ? I
DPSK mod, GFSK mod, GMSK mod … however not FSK.
Do you have any example for transmitting flow graph in GNU radio with
? If yes, could you please give any hint ?
Thank you and best regard

On Mon, Aug 31, 2015 at 7:31 PM, Hoang Nguyen T. [email protected]

Thank you Marcus.

On Thu, Sep 3, 2015 at 4:05 AM, Marcus Müller [email protected]


there’s the frequency modulator block. I think this is what you’re
looking for.

Best regards,