Re: [Discuss-gnuradio] phase coherence for N210 and SBX

[Marcus Müller]

Hi Marcus, hi Pengyu,

I'd like to make an addition to that:
modern gr-uhd uses a timed command to start streaming samples, so the
CORDICs in both USRPs should be aligned. But:
It doesn't inherently use timed commands for tuning; you should do
something like:

usrp_source0.set_command_time(uhd_source0.get_time_now()+0.1)
usrp_source0.set_center_freq(frequency)
usrp_source0.clear_command_time()
time.sleep(0.15)

after you configured your usrp_source and before your top_block is
.start()ed.

Generally, I like
http://files.ettus.com/manual/page_sync.html
because it explains a bit why and how things work.

Greetings,
Marcus


On 04/24/2015 12:28 AM, Marcus D. Leech wrote:
> On 04/23/2015 06:23 PM, Pengyu Zhang wrote:
>> Thanks for the inspiring tips. I did not use the WX GUI scope for
>> checking the phase offset. Instead, I log the baseband signal
>> received by each RX antenna. Then, I plot the IQ constellation of the
>> received baseband for checking their phase offset.
>>
>> Can you be a bit more specific when you say the "multi_usrp object"
>> and the "timed commands"? Are there tutorials that I can follow step
>> by step for using the two functions you mentioned? Your comments are
>> very helpful :)
>>
> A source/sink block in Gnu Radio uses an underlying multi_usrp object,
> so all you have to do is configure your source block for two channels,
> with
>   two devices, and use
>
> addr0=<first-device-ip-addr,addr1=<second-device-ip-addr>
>
> In the device arguments.
>
> Also, recent gr-uhd (3.7.6.1 and newer at least) use timed commands,
> so phase-zeroing will happen after a tune automatically, without you
> having
>   to do anything.
>
>
> The top of the UHD manual is here:
>
> http://files.ettus.com/manual/page_devices.htmlhttp://files.ettus.com/manual/page_devices.html
>
>
> The Doxygen docs are here:
>
> http://files.ettus.com/manual/page_coding.html
>
> The documents for gr-uhd are part of the Gnu Radio documentation:
>
> http://gnuradio.org/doc/doxygen/classgr_1_1uhd_1_1usrp__source.html
>
>
>
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