Re: [Discuss-gnuradio] Interest in beamforming and GNSS receivers

[Carles Fernandez]

Thank you very much for your informative responses. Now things are clearer to me: the possibility of building an antenna array combining two or more USRPs is just exciting! I'm also delighted with the option of using an external reference clock. I definitely will buy at least one USRP for the first experiments and the development of a simple GPS receiver. If my progress is adequate, I will go for the multi-antenna approach.

I will keep you informed, and surely I will come often with new questions.  Thanks again for those great sources of information, I'm really enjoying while exploring them.

Cheers,
Carles.

On Jan 31, 2008 10:33 PM, Martin Dvh <address@hidden> wrote:

Pavol Ďuriš wrote:
> Hi all,
>
> I have an interest in radioastronomy. I plan to make simple beamforming
> phase array (primary with 4 and later with 8 antennas) with USRP (later
> with 2) and GNU Radio. I am inspired by LOFAR radiotelescope.
> Now I collect all available information about using GNU Radio and USRP
> for it.
>
> Martin, could you send more information about your solution, project
> (url etc.) ?

Info about connecting murli-USRPs:
 http://gnuradio.org/trac/wiki/MultiUsrp
 http://gnuradio.org/trac/wiki/USRPClockingNotes
 http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-examples/python/multi_usrp
This last one is also in your gnuradio source directory:
 gnuradio-examples/python/multi-usrp

It has been a while since I last used this setup, so there might be some bitrot.
(incompatibilities between the multi-usrp fpga firmware (rbf-file) and the latest gnuradio code and support for the latest daughterboards.)
But if this is the case then it should be solvable by implementing the latest changes to the standard USRP firmware to the multi-USRP firmware.


There is not much info about my phase-array experiments online.
I know, I should update my website more often, but I am better at writing code then at writing human-readable text.
I do haver a snapshot of my CMA (Constant Modulus Algorithm) adaptive phase-array code.
This code automatically adapts to multiple FM, GMSK, QPSK or M-PSK sources.
It should be able to extract multiple sources on the same frequency by automatically nulling the other sources out when extracting one.
(max number of sources == number of antenna's used)

Note that this code only works with phase-coherent daughterboards (boards which use the USRP-clock as refclock)
This means allmost all daughterboards except TVRX.
(Which is too bad since I want to extract multiple broadband FM stations, for now I use undersampled basicRX)
The code is at:
http://www.olifantasia.com/projects/gnuradio/mdvh/CMA_phase_array/

Other code of mine can be found at:
http://www.olifantasia.com/projects/gnuradio/mdvh/
or
http://gnuradio.org/trac/browser/gnuradio/branches/developers/nldudok1
or (when it has stabalized) in GnuRadio trunk

Greetings,
Martin

> Thanks,
> Pavol
>
> PS: I haven't USRP yet. However, I am buying my first USRP, right now :)
>
> Martin Dvh wrote:
>> Carles Fernandez wrote:
>>
>>> How well are they synchronized?
>>>
>> They run off the same 64 MHz clock, so are synchronised.
>> I have even used two connected USRPs running of the same clock (one is
>> master and exports its clock to the slave USRP)
>> (You use an additional flatcable between the USRPS and an align
>> software block in gnuradio which aligns the samples)
>> This gives you 8 ADCs. This means 8 real channels or 4 complex channels.
>>
>> I used this setup for a phase array with 4 DBSRX daughterboards.
>> (DBSX daughterboards use complex sampling so they need two ADCs)
>> DBSRX boards also support the GPS frequencies and are a lot cheaper,
>> so you might want to consider them.
>> But they are receive only.
>>
>> You can even go higher and connect 4, 8 or 16 USRPS.
>>
>