Re: [Discuss-gnuradio] The shortest pulse length

[Eric Blossom]

On Fri, Mar 02, 2007 at 12:41:40AM -0800, seph 004 wrote:

> I am only using 1 daughterboard. Sorry about the duc0 = 0
> inclusion. It's something I neglected to remove when I was editing
> the original file. I don't think it should have any effect on what I
> am seeing though. I set the duc frequency to 0 because I wanted to
> transmit at baseband. I've already built the signal I want in the
> gr.vector, I just want the daughterboard to pass it as is. I've
> managed to do that with usrp_siggen.py. By setting the -f option to
> 0 and the -w option to some frequency, I get a waveform of the -w
> frequency at the daughterboard output. I'm pretty sure (0, 0) is
> TXA, and (1, 0) is TXB. My waveform does appear at the TXB output
> when I run the script. The problem is the pulse duration I'm seeing
> is much shorter (about 1/10) than what I expect.
> 
> Regards
> Lance 

Unless the total number of samples comes out to a multiple of 128,
some will left in the host buffer and not transmitted across the USB.
Try padding your vsource data with zeros to a multiple of 128.

Eric



> 
> ----- Original Message ----
> From: David Scaperoth <address@hidden>
> To: seph 004 <address@hidden>
> Cc: address@hidden
> Sent: Thursday, March 1, 2007 7:15:36 PM
> Subject: Re: [Discuss-gnuradio] The shortest pulse length
> 
> 
> 
> 
> On 3/1/07, seph 004 <address@hidden> wrote:
> 
> 
> 
> This is what I did:
> 
> def build_graph ():
>     nchan = 1
>     interp = 512
>     duc0 = 0
>     duc1 = 0
>     fs = 250e3                                        #2nd sample rate 
> between usb and dac
> 
>     max_dev = 32e3                              #1st sample rate divided by 4 
> (1st = 2nd sample rate)
>     gain = 16e3
>     k = 2 * math.pi * max_dev / fs
>     vec1 = Numeric.arange (0.624, 0.656, 0.0000128)
> 
>     vsource = gr.vector_source_f(vec1, False)
>     fmmod = gr.frequency_modulator_fc (k)
>     amp = gr.multiply_const_cc(gain)
>        
>     fg = gr.flow_graph ()
>     
>     u = usrp.sink_c (0, interp, nchan)
> 
>     tx_subdev_spec = (1, 0) #usrp.pick_tx_subdevice(u)
>     m = usrp.determine_tx_mux_value(u, tx_subdev_spec)
>     u.set_mux(m)
>     subdev = usrp.selected_subdev(u, tx_subdev_spec)
>     subdev.set_enable(True)
> 
>     
>     sample_rate = u.dac_freq () / interp
>     u.set_tx_freq (0, duc0)
>     u.set_tx_freq (1, duc1)