Re: [Discuss-gnuradio] Why does a SINE wave have a real part?

[sudhindra aithal kota]

--- cswiger <address@hidden> wrote:

> On Fri, 26 Aug 2005, sudhindra aithal kota wrote:
> 
> > Hi,
> >  I am running the usrp_siggen.py program with the
> > option -m 0x98. The signal transmitted is a SIN
> wave.
> > My understanding of this option is, Channel 0's I
> part
> > is connected to DAC0 and Channel 0's Q part is
> > connected to DAC1.
> 
> That is correct.
> 
> 
> > Since for a SIN wave the real part
> > does not exist, there should not be anything
> > transmitted via DAC0.
> 
> Whoa - 'SIN' is just the shape and our signal can
> have
> real and imag components. Maybe confusing the
> real/cosine imag/sin
> analysis with our real world signal ?
> In usrp_siggen.py the signal source is complex
>   self.siggen = gr.sig_source_c, and the signal sink
> is
> complex   self.usrp = usrp_sink_c


Still confused here. 
1)If we take a Sine wave isnt it true that it does not
have any real parts?


> 
> Actually we were just discussing, due to the
> digital-upconverters
> on the 9862 chips, sending a signal to either DAC
> will result
> in output from both, even if one channel is all
> zeros.
> 
> >  Then I connect the TX and RX part of the USRP
> board
> > and use the usrp_oscope.py function with the
> option -m
> > 0x33333310 to view the signal I have transmitted.
> This
> > would mean connect ADC0 to the I part of
> Interpolator0
> > and ADC1 to Q part of Interpolator0.
> 
> I think you mean digital-downconverter, not
> Interpolator0,
> those are in the Tx path - were in the Rx path now.
> Otherwise
> yes, ADC0 to the I input of DDC0 and ADC1 to the Q
> input.
> Do you have both two cables linking the boards or
> one? ADC1
> gets it's input from J18.

I have 2 cables linking the boards. 

> 
> > I see 2 signals
> > with a phase difference of 90. Where is the second
> > signal coming from, when I am transmitting only
> one
> > signal?
> >
> 
> the source in usrp_oscope.py is also complex from
> the usrp
> u = usrp.source_c  and with 1 channel is getting the
> data
> from digital-downconverter 0.   Interestingly, with
> these
> arguments:
> 
> ./usrp_oscope.py -d 64 -c 1e6
> ./usrp_siggen.py -c 1e6 -f 10e3 -i 64
> 
> with only one cable from J19 to J48 there's a big
> 450 unit
> signal, with another cable from J18 to J49 connected
> it
> becomes small with an amplitude of 25 ;)
> 
> I'm still exploring the possibilities myself.
> 
> --Chuck
> 
> 



        

        
                
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