Re: [Discuss-gnuradio] test_usrp_standard_tx[rx].cc doubts...

[Eric Blossom]

On Mon, Jul 18, 2005 at 06:10:44PM -0700, Angilberto Muniz Sb wrote:
> Matt
> 
> While playing with "test_usrp_standard_tx[rx].cc"
> setting
> "-c" flag, I was expecting the folloing:
>  
>      x    x     x
>     x    x     x
>    x    x     x 
>   x    x     x
>  x    x     x         ......
>  
> But its not what I am getting. 
>  
> If I change the code that deal with the "counting
> flag" as:
>  
>      if (counting_p){
>        for (int i = 0; i < N; i++) {
>       
>       counter += delta;
>       
>       buf[i] = host_to_usrp_short (counter & xffff);
>       
>       if (i < N/2) delta = 1;
>       else delta = -1;
>        }
>      }
>  
> I would expect:
>  
>      x       x
>     x x     x x 
>    x   x   x    x 
>   x     x x      x
>  x       x         x  ......
>  
> I dont get it either...

These are *very* low frequeny ramps.  They are most likely not getting
through the transformer on the basic tx board.

> Am I correct in my assumptions?

More or less.

> When I watch the DAC on the scope or when I plot it
> whith Matlab I see some breakups like its outputting
> in bursts... Is this the correct/expected behavior?

Should be continuous, but it will be hard to see.

You'll be much better off using gnuradio-examples/python/usr/usrp_siggen.py

If you're getting underruns, use a bigger value for the interpolation
factor.  Try using -i 128.  That will result in 1MS/sec (complex)
across the USB.

> Lets suppose I want to generate 10khz sin/cos wave --
> can "test_usrp_standard_tx.cc" handle it whith some
> modifications?


Note again that you won't be able to see a 10kHz sine wave at baseband
due to the transformer.  You can use the --duc-freq=1M option to put
it up at 1MHz.

address@hidden usrp]$ ./usrp_siggen.py --help
usage: usrp_siggen.py [options]

options:
  -h, --help            show this help message and exit
  --sine                generate a complex sinusoid [default]
  --const               generate a constant output
  --gaussian            generate Gaussian random output
  --uniform             generate Uniform random output
  -iINTERP, --interp=INTERP
                        set fgpa interpolation rate to INTERP
  -fFREQ, --freq=FREQ   set waveform frequency to FREQ
  -aAMPL, --amplitude=AMPL
                        set waveform amplitude to AMPLITUDE
  -oOFFSET, --offset=OFFSET
                        set waveform offset to OFFSET
  -cFREQ, --duc-freq=FREQ
                        set Tx DUC frequency to FREQ
  -nNCHANNELS, --nchannels=NCHANNELS
                        set number of output channels to NCHANNELS
  -mMUX, --mux=MUX      set output mux register


Eric