[Discuss-gnuradio] usrp tx documentation/confusion

[Erik Tollerud]

I've been trying to work out how to do some things on the transmit
side of gnuradio, and I've noticed there's something of a dearth of
documentation.  Most of it amounts to "its just like receive, only
backwards."  That's probably fine for people with signal processing
background (which may be the majority of this community...), but I
find myself getting confused... by looking at some of the examples, I
get a sense of how to initialize all the components in python, but if
I do anything beyond them, I get unexpected results.  For example, I
took siggen_min2.py and modified it so that instead of outputting a
pure sine wave, it output sin(wt)+cos(2wt).  This did not put anything
resembling sin(wt)+cos(2wt) on the output of the tx board. 
Furthermore, chaging w does not some to alter the waveform at all -
only calling u.set_tx_freq changed the output freqency.

Again, it may be that there's simple something basic here that most
people know because they've worked with this before (in which case,
there's no need to improve the documentation), but for someone without
specific background (i.e. I'm in math and physics), the documentation
is difficult to follow on the transmit end.