Re: [Discuss-gnuradio] unknown phase-relation between rx and tx

[wolfgang buesser]

Just to make sure:

I am using LF RX/TX-boards.
TX and RX are on the subdev (thus using the same AD9862)

Thanks
Wolfgang



Jonathan Friedman-2 wrote:
> 
> Unless I misunderstand what you are doing, what you are describing is
> the coherence error of the system. The long-answer made short is "no".
> You have to calibrate it out or otherwise live with it. The TX and RX
> paths of the USRP are derived from separate hardware local oscillators
> so there will always be an unknown phase error between them. What's
> worse is that it will vary slowly and dynamically as temperature and
> voltage change during system operation.
> 
> Cheers,
> -Jonathan
> 
> On Sun, Jun 22, 2008 at 2:42 AM, wolfgang buesser
> <address@hidden> wrote:
>>
>> Hi,
>>
>> Iam using
>>   gr.sig_source_s (self.usb_freq (), gr.GR_CONST_WAVE, 0, 0, 0)
>> to generate a carrier and
>>   usrp.source_c(nchan=2,decim_rate=self.interp) to resample it at the
>> same
>> frequency.
>>
>> I get what I expect: 2 complex numbers which are pretty constant. But
>> with
>> every restart
>> of the program the phase changes (apparently by the same amount for both
>> channels). The
>> amplitude does not vary much from run to run.
>>
>> It seems to me, that the phase relation between the interpolator in the
>> TX
>> and the decimator in
>> the RX changes with every restart.
>>
>> Is there a way to "reset" the  interpolator/decimator so that I get the
>> same
>> reading for every start
>> (as long as I don't change frequencies) ?
>>
>> Thank's
>>   Wolfgang
>> --
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>>
>>
>>
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> 
> 
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