Re: [Discuss-gnuradio] upconversion problem

[crjqq]

--- On Thu, 7/16/09, Brian Padalino <address@hidden> wrote:

> From: Brian Padalino <address@hidden>
> Subject: Re: [Discuss-gnuradio] upconversion problem
> To: address@hidden
> Cc: address@hidden
> Date: Thursday, July 16, 2009, 5:44 AM
> On Wed, Jul 15, 2009 at 5:59 PM,
> <address@hidden>
> wrote:
> >
> > I'm using a FLex900 daughterboard with the usrp. I
> used the usrp_siggen.sh script from the /gr-usrp/apps
> folder.
> > I wanted a sinusoidal carrier(no modulation) at
> 915Mhz. However after running the code I observe max. power
> at 920Mhz in the spectrum analyzer and a small peak at
> 915Mhz.
> >
> > I am not clear how the wfreq(waveform freq) parameter
> in the foll. line of code:
> >  /* Set up the signal source */
> >  siggen = gr_make_sig_source_c(input_rate,
> GR_SIN_WAVE, wfreq, amp);
> >
> > affects the output.
> >
> > The output that was displayed was:
> > --------------------------
> > which:    0
> > interp:   128
> > rf_freq:  9.15e+08
> > amp:      5.000000
> > nsamples: 0
> > Subdevice name is Flex 900 Tx MIMO B
> > Subdevice freq range: (8e+08, 1e+09)
> > mux: 0x000098
> > usrp->dac_freq(): 128000000
> > usrp->interp_rate(): 128
> > baseband rate: 1e+06
> > target_freq:     915000000.000000
> > ok:              true
> > r.baseband_freq: 920000000.000000
> > r.dxc_freq:      -5000000.000000
> > r.residual_freq: 0.000000
> > r.inverted:      0
> > --------------------------
> 

> 
> If you send out strictly DC when you upconvert to 915MHz,
> you will see
> something at 915MHz.  Positive frequencies shift the
> carrier higher,
> negative frequencies shift the carrier lower.
> 
> > I dont know if I'm setting incorrect values or using a
> wrong approach. Please help me out.
> 
> Hope this helps.
> 
> Brian
> 

> What I think is happening is you are sending out a tone at
> 5MHz.  What
> is the value of wfreq?


Thanks Brian. The default wfreq value in code is 100Khz. can anyone explain the 
exact significance of r.dxc_freq and r.baseband freq?

Also, I think the documentation mentions that frequency tuning is in 4Mhz 
steps. if it can tune to 920Mhz, why not 916Mhz which is closer to 91Mhz?

Code comments state that the usrp_sink_base.tune() function is a
"High-level "tune" method. Works for the single channel case.
This method adjusts both the daughterboard LO and the DUC so that DC in the 
complex baseband samples ends up at RF target_freq."

Does this mean I can have more control using another "low-level" method? which 
one would that be?

-Rush