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Re: [Discuss-gnuradio] Locking USRP2 to external 10MHz reference in the

From: Josh Blum
Subject: Re: [Discuss-gnuradio] Locking USRP2 to external 10MHz reference in the UHD/GRC universe
Date: Sun, 21 Nov 2010 21:37:01 -0800
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20101027 Thunderbird/3.1.6

The capability is already there. If you need an example, take a look at the generated python code when you enable the ref clock for the uhd source or sink block in GRC. -Josh

On 11/21/2010 05:44 PM, Thomas Hobiger wrote:
Hi Josh,

I understand that the mimo blocks use the external ref automatically,
but how to get this done with the UHD Single source block? In one of the
prior mails you mentioned some Python code together with the XML wrapper
changes. Can you tell me explicitly where to put that code?


On 08/27/2010 01:28 AM, Josh Blum wrote:
The locking to external ref in the uhd mimo blocks is automatic. If
you are receiving samples, then the individual channels are aligned to
their timestamps. Otherwise gnuradio gets a 404 samples not found.

You can also see the alignment if you look at magnitude of ch0 vs ch1
on a scope sink (assuming the RF input is identical). I have tested
this with Basic RX boards; what daughterboards are you using?


On 08/26/2010 07:40 AM, Johannes Wenzel wrote:

I'm using a mimo (2x2) USRP2 system. Both of the receiver USRP2
receive a PPS- and a Clock-Signal provided by one GPS card. In grc I
use the uhd_mimo_source block and two file_sink to receive and save
the data sent. After starting RX the USRP2 mimo system seems to lock
to the reference clock and reset the timer on PPS. Is this true? Or
do I have to configure the block to do so? If I test the data with
correlation it fails, which seems to be an indicator that at least
the reference clock is not locked on.

Is the uhd_mimo_source block automatically locked to external
reference clock if used or do I have to configure it?



Am 23.08.2010 um 05:02 schrieb Josh Blum:

Swig brings in the clock config struct into python. The python code
looks like:

from gnuradio import uhd
ccfg = uhd.clock_config_t()
ccfg.ref_source = ccfg.REF_SMA
ccfg.pps_source = ccfg.PPS_SMA
ccfg.pps_polarity = ccfg.PPS_POS

so the the grc xml wrapper you need that bit of code along with



On 08/22/2010 04:52 PM, Marcus D. Leech wrote:
How do I arrange to lock the USRP2 to an external 10MHz reference
in the
UHD+GRC world? Is there an "arg" I can pass when I
create the UHD USRP2 simple source in GRC?

This is for some pulsar research, where an external stable reference
makes life soooo much easier.

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