I'm exploring the LF spectrum (< 500 kHz) using a USRP N210+LFRX+active loop antenna, and GR 3.7. I'm pulling my hair out trying to down convert the USB as I can't get the LSB rejected. My GRC flow graph is here:https://dl.dropboxusercontent.com/u/49570443/test.grc.png
It is based on figure 5 of below; quadrature, direct down conversion with Hilbert transform.http://www.arrl.org/files/file/Technology/tis/info/pdf/98qex003.pdf
I'm taking the real output (i.e. the DAC hooked to the LFRX channel 1) of the N210 at 25 Msps with 0 Hz DDS, then low-pass filtering at 550 kHz and decimating to 1.25 Msps. This seems to provide better rejection of the AM band than using the DDS tuning internal to the N210.
I then use the translating FIR filter to tune a 2 kHz passband, decimated to 5 ksps.
Problem comes when I try to do the LSB rejection with the Hilbert. I think I'm using it correctly; I have tried swapping the Re and Im outputs of the Hilbert with no luck. Maybe there is something conceptually I am missing since I am starting with a real signal. I have done SSB demod with complex USRP signal with no problems.
Any ideas of what I am doing wrong? This should be basic stuff
but I'm not getting something.
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