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[Discuss-gnuradio] Trouble with SSB demod of real signal
From: |
Louis Brown |
Subject: |
[Discuss-gnuradio] Trouble with SSB demod of real signal |
Date: |
Sun, 16 Feb 2014 11:10:10 -0600 |
Hi,
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.
Thanks,
Lou
- [Discuss-gnuradio] Trouble with SSB demod of real signal,
Louis Brown <=