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Re: [Discuss-gnuradio] UHD Source Block and N210/SBX Synchronisation

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] UHD Source Block and N210/SBX Synchronisation
Date: Tue, 01 Mar 2016 10:43:47 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 03/01/2016 04:57 AM, Nigel Steed wrote:

Hi All,


Has anyone managed to use/modify the UHD Source Block to phase synchronise multiple N210/SBX ?


From what I have read I must perform the following


(1)    Configure to use external references (10MHz and 1PPS) using the options in the UHD Source Block

(2)    Use integer N mode for the PLL

(3)    Re-tune the frequency of the PLL’s on multiple N210/SBX at the same using a time command

(4)    Align the CORDIC’s at initialisation and after a re-tune from (2) above by stopping and starting a stream disciplined to a time command which issues a reset to the CORDIC’s at the same time






The only thing really missing in gr-uhd is the ability to do timed commands.   You can force integer-N mode by constructing your own
  tune_request that includes the integer-N option.  You'd use a feature from the latest Gnu Radio to help you with this, because it involves
  getting into the internal structure of a tune_request blob.   So, use the "Python module" block, and in that Python do something like:

def integer_N_tune_me(freq):
    r = uhd.tune_request(freq)
    r.args = {"mode_n" : "integer"}
    return r

Then, in your UHD source/sink block, instead of using your target frequency directly, use:


Martin could probably comment on the feasibility of adding timed commands to gr-uhd.

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