Re: [Discuss-gnuradio] upconversion problem

[Brian Padalino]

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
> --------------------------

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

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