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

[Johannes Wenzel]

Hi,

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?

Thanks

 Johannes.

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
> 
> $(id).set_clock_config(ccfg)
> 
> -Josh
> 
> 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.
>>