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

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] phase coherence for N210 and SBX
Date: Fri, 24 Apr 2015 09:07:40 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

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:


after you configured your usrp_source and before your top_block is

Generally, I like
because it explains a bit why and how things work.


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 ( 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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> Discuss-gnuradio mailing list
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