Re: [Discuss-gnuradio] Two USRP B210s with Octoclock-G (Samith Abeywickrama)

[Luca Pascale]

Hi Samith,

to calibrate phase offset you can use a "calibration signal".
Using a (phase) balanced power divider you can feed the 4 rf input with
this calibration signal and use it to estimate differential phasors
between the 4 channels taking one of them as reference (i.e. the first).
You will have 3 significant differential phasors.

You need to do this after each retune of the boards on a given frequency.
Then you can apply the correction factors to the channels 2,3,4 once you
acquired the signals you want to use to estimate DOAs.

Calibration Signal:
- CW tone if you are interested on a single specific frequency (not real
world condition)
- wideband noise
Also depends on your implementation...(are you using a FFT Filter-bank
and estimate DOAs for each FFT bins or ... are you working "narrowband").
To estimate correction factors I suggest to do some averaging.

Moreover if your DF algorithm is (in some measure) sensitive to signals
amplitude I suggest to perform also amplitude calibration not just phase
calibration.
You can estimate it using the differential phasors.

Regards,
Luca




>Well, that's a bit up to your implementation. Probably, you want to have
>something that you know the direction of and use it to find the
>individual phase offsets, and find a complex de-rotating factor.


>On 06.09.2016 10:52, Samith Abeywickrama wrote:
>> Hi Marcus,
>>
>> Thank you very much. Btw, how can we calibrate the relative phase
offsets?
>>
>> Samith
>>
>> On Tue, Sep 6, 2016 at 4:34 PM, Marcus M?ller
>> <address@hidden <mailto:address@hidden>> wrote:
>>
>>     Yes, you can  Offering synchronization using external 10MHz and
>>     PPS signals is the purpose of the Octoclock-G !
>>
>>     However, the B210's LOs will have a random phase after every
>>     tuning, so you must calibrate the relative phase offsets every
>>     time you tune
>>
>>     Best regards,
>>
>>     Marcus
>>
>>
>>     On 06.09.2016 10:21, Samith Abeywickrama wrote:
>>>     Hi all,
>>>
>>>     I'm going to implement MUSIC(Multiple Signal Classification)
>>>     algorithm to find Angle of Arrival of signal using two USRP
>>>     B210s. Therefore I have 4 antennas. But I need to synchronise my
>>>     two USRP B210s. May I know that can I use Octoclock-G with my
>>>     USRP B210s without any problem? Thank you in advance.
>>>
>>>     --
>>>     Best Regards!
>>>     Samith
>>
>>
>>
>>
>> --
>> Best Regards!
>> Samith