[Discuss-gnuradio] help with tuning RFX2400 MIMO_b, weird RX results

[George Nychis]

Hi all,

First, I'm sorry if my actions are shunned upon (C++ daughterboard code 
outside the mainstream repository), but I could sincerely use help with 
a deadline approaching next week.

I am trying to use code that Per started for tuning a MIMO_b RFX card in 
C++.  Using the base code he gave me, I was able to get the transmitter 
working bot not receiver.

I am trying to receive a GMSK transmission.

Here is a normal reception after tuning the card in python:
http://cyprus.cmcl.cs.cmu.edu/tmp/flex_graphs/gmsk_regular.jpg
http://cyprus.cmcl.cs.cmu.edu/tmp/flex_graphs/gmsk_regular_rvi.jpg

... we get a nice clean circular transmission.

When I attempt to receive using the C++ RX code, that I modified to set 
the RX gain, I get the following square-like transmission:
http://cyprus.cmcl.cs.cmu.edu/tmp/flex_graphs/gmsk_flex.jpg
http://cyprus.cmcl.cs.cmu.edu/tmp/flex_graphs/gmsk_flex_rvi.jpg

Based on these results, does anyone have any insight in to what I may be 
tuning incorrectly?  I thought it might be the gain setting, but I 
mimiced the set_gain() method exactly with the python code and ensure 
the write_aux_dac() and set_pga() values are the same:
https://moo.cmcl.cs.cmu.edu/trac/cmu_sdrg/browser/dboard_code/db_flexrf_mimo.cc#L193

To tune the cards, I am using:
db_flexrf_mimo dboards(d_urx, d_utx, 0);
dboards.configure(d_rf_freq, 45, 0);
dboards.configure(d_rf_freq, 0, 1);
dboards.select_tx();

I followed through almost every function call and I can't seem to find 
the different in tuning between my code and the python.

I'd greatly appreciate any insight.

Thanks!
George