[Discuss-gnuradio] Strange behaviour in GRC for a simple FFT/IFFT flow-graph

[Kresimir Dabcevic]

Hi all!

When constructing a simple flow graph Signal_source(f)->Throttle(f)->Stream_to_vector(vf)->Forward_FFT(vc)->Reverse_FFT(vc)->Vector_to_stream(c)->WX_GUI_FFT_sink(c), the sink exhibits strange behaviour, showing frequency (and the image frequency) different than the one I'm creating with the signal source, e.g. for f=1kHz, sink shows 15kHz and -15kHz whereas for f=15 kHZ it shows 1kHz and -1kHz.

On the other hand, if I create a complex signal using signal source, or use Float_to_complex block before feeding it to Stream_to_vector, the results are as expected.

Is this a glitch in GR (I'm using GRC 3.6.4.1.), or is there something I'm missing here?

The flow graph and the result for f=1kHz are as follows:

http://imageshack.us/photo/my-images/194/xfvr.jpg/

http://imageshack.us/photo/my-images/826/dj2p.jpg/

*f=float; vc=vector of complex; c=complex

Thanks in advance!