Re: [Discuss-gnuradio] Maximum I/Q signals frequency limit for TX

[Eric Blossom]

On Mon, Apr 23, 2007 at 09:42:46AM -0700, Matt Ettus wrote:
> Shaiful wrote:
> >Hi guys,
> >
> >I'm trying to generate complex I/Q waveforms using
> >this command (for 700 KHz):
> >
> >./usrp_siggen.py -T A -w 700000 -f 0
> >
> >>From the mailing list, I've read that the USRP can
> >transmit up to 44 MHz.  
> >
> >Unfortunately I can only transmit clean quadrature I/Q
> >signal only up to 700 kHz.  Above the frequency, I'm
> >starting to see two or more waveforms for each
> >generated quadrature I/Q signals.

As Matt mentions below, there are two things you can adjust: the RF
center frequency with -f RF_FREQ and the baseband data sample rate.
To increase the baseband sample rate, use the -i INTERP option.  Try
-i 32.  That'll give you a baseband sample rate of 128M/32 = 4M
samples/s.  The defaults give a baseband sample rate of 1MS/s which is
consistent with your report.

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

options:
  -h, --help            show this help message and exit
  -T TX_SUBDEV_SPEC, --tx-subdev-spec=TX_SUBDEV_SPEC
                        select USRP Tx side A or B
  -f RF_FREQ, --rf-freq=RF_FREQ
                        set RF center frequency to FREQ
  -i INTERP, --interp=INTERP
                        set fgpa interpolation rate to INTERP [default=64]
  --sine                generate a complex sinusoid [default]
  --const               generate a constant output
  --gaussian            generate Gaussian random output
  --uniform             generate Uniform random output
  -w WAVEFORM_FREQ, --waveform-freq=WAVEFORM_FREQ
                        set waveform frequency to FREQ [default=100000.0]
  -a AMPL, --amplitude=AMPL
                        set waveform amplitude to AMPLITUDE [default=16000.0]
  -o OFFSET, --offset=OFFSET
                        set waveform offset to OFFSET [default=0]

> >Unfortunately I can only transmit clean quadrature I/Q
> >signal only up to 700 kHz.  Above the frequency, I'm
> >starting to see two or more waveforms for each
> >generated quadrature I/Q signals.
> >
> >If I increase the frequency further to 1 MHz, USRP
> >only generate one signal from TX_A connector, there is
> >no signal from TX_B connector.   Both TX_A and TX_B
> >connectors are on daughter board of 'USRP Tx side A'
> >as indicated by '-T' flag. FYI, I'm using LFTX
> >daughter board not the Basic ones.
> >
> >If I transmit more than 1 MHz, the frequency is still
> >cap at 1 MHz.
> >
> >Any idea what is happening and how to get higher
> >frequency?
> 
> 
> Yes.  the -w frequency is the baseband frequency.  To go higher you need 
> to change the -f frequency which is the carrier frequency, or lower the 
> interpolation rate.
> 
> Matt