Re: [Discuss-gnuradio] doubt about the tune()

[Eric Blossom]

On Wed, Aug 04, 2010 at 05:08:44PM +0800, intermilan wrote:
> 
> hi all:
>        I recently run the test_usrp_standard_tx/rx.cc to do some test.and 
> after I run the test_usrp_standard_tx.cc, I got the follow information:
> which:    0
> interp:   64
> rf_freq:  2.5e+09
> amp:      30000.000000
> nsamples: 3.2e+07
> Subdevice name is Flex 2400 Tx
> Subdevice freq range: (2.3e+09, 2.7e+09)
> mux: 0x000098
> baseband rate: 2e+06
> target_freq:     2500000000.000000
> ok:              true
> r.baseband_freq: 2504000000.000000
> r.dxc_freq:      -4000000.000000
> r.residual_freq: 0.000000
> r.inverted:      0
> xfered 3.2e+07 bytes in 4 seconds.  8.002e+06 bytes/sec.  cpu time = 0
> 
>       as you can see, I want to set the frequency at 2.5G(RFX2400) ,but there 
> is a parameter called r.basebande=2.504G.I know it is the return valus of the 
> tune().but I want to know what is the function of this parameter and how did  
> 2.504G come out. can anyone help me to figure it out?
>       Besides,why the frequenct of the DUC is set at -4M? how did it come out?

It moves the DC offset 4MHz away from the center of your desired
spectrum.  r.baseband_freq + r.dxc_freq = target_freq.

Eric