Re: [Discuss-gnuradio] usrp tx documentation/confusion

[Erik Tollerud]

Ah - I missed the usrp_siggen.py... at any rate, the situation still
arises that I don't get anything resembling sin(wt)+cos(2wt)... I
guess the biggest aspects of my confusion come from the interpolation
(specified in the usrp.sink_c constructor) - is that interpolating
between 2 points on the curve that's input into the sink, or does it
just sample the signal however often the interpolation is and fill in
the rest?  And for that matter, I don't see why the u.set_tx_freq is
controlling the output - shouldn't the frequency specified for the
input sine wave change something (at least if its around the tx
frequency)?

Again, if there's some web site that you know of that will explain
this all, I'm fine with figuring it out with a little guidance... I
just am getting somewhat buried in the terminology/conventions for
something that seems it should be fairly simple...

On 5/5/06, Matt Ettus <address@hidden> wrote:
> On Fri, 2006-05-05 at 15:45 -0700, Erik Tollerud wrote:
> > 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.
>
> I agree that there is definitely a dearth of documentation, especially
> for TX.
>
> The [unstated] purpose of siggen_min2 is to transmit different signals
> to TX daughterboard A and TX daughterboard B.
>
> In general, without really changing the firmware, any signal sent to
> DB-A will output the I signal on one output and the Q on the other.  The
> same goes for DB-B.
>
> For what you are trying, I would suggest working with usrp_siggen.py
> unless you want to use multiple TX daughterboards.
>
> Matt