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 <[EMAIL PROTECTED]> 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. > >> > > > >
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