Re: [Discuss-gnuradio] 4 RX with 2 WBXs?

[Jason Abele]

On Fri, Sep 10, 2010 at 03:59:34PM -0400, Scott Storck wrote:
> Jason and Marcus, thanks for your responses.  I was afraid that this was the
> case.
> 
> Is there a daughterboard out there (besides the BasicRX) that can support 4
> antennas on a single USRP?

Just LFRX

> 
> The other option that would work for me is connecting antenna 0 to WBX 0 and
> connecting antennas 1-3 to WBX 1 through a commutator to switch them at a
> sub-1 kHz frequency.  Can you tell me if any of the unpopulated headers on
> the WBX board are digital outputs that could potentially be used to generate
> a switching signal and/or low rate ADC inputs that could be used to sample a
> switching signal generated elsewhere?

You could already switch between the 4 antenna ports (2 on each WBX)
using the antenna switches built into the WBX at sub-kHz speeds.  If you
really needed to solve the antenna switching problem externally, there
are GPIOs available on the some of the 0.1" pin headers, check the
schematics here:

http://code.ettus.com/redmine/ettus/projects/public/documents

> 
> Finally, what it would take for 2 USRPs to operate a total of 4 WBXs
> coherently?  I assume this would at least require connecting Clock Out on
> USRP0 to Clock In on USRP1, but is that enough to get all 4 WBX PLLs locked
> together?  Also, does using two USRPs simply mean that the max USB data rate
> for each USRP is halved, or is the effect more severe?

If you want 4 coherent RX using WBX, what you want is 4 USRP2's, 4 WBX's
and a GPSDO to supply 10MHz Refclock and PPS signals to all the USRP2's.
You would also need 4 separate Gigabit ethernet ports on your host PC.
Then, you will have 25Msps from each receiver.

> 
> Thanks,
> Scott
> <address@hidden>
> 
> On Fri, Sep 10, 2010 at 3:19 PM, Jason Abele <address@hidden> wrote:
> 
> > On Fri, Sep 10, 2010 at 12:04 PM, Scott Storck <address@hidden> wrote:
> > > I have a USRP and two WBX daughterboards.  Is it possible to use 4
> > > independent RX antennas (all tuned to the same frequency) with this
> > hardware
> > > setup?
> >
> > Scott,
> >
> > The WBX has only one (I/Q) receiver per daughterboard.  The two
> > Antenna ports (TX/RX and RX2) are for convenience to enable a single
> > Antenna on the TX/RX in half duplex or a dedicated RX antenna on RX2.
> > The WBX merely switches the input of a single RX chain between those
> > two antenna ports based on user settings.
> >
> > So, only 2 receivers are possible with your USRP + 2 WBX setup
> >
> > Jason
> >
> 
> On Fri, Sep 10, 2010 at 3:22 PM, Marcus D. Leech <address@hidden> wrote:
> 
> I have a USRP and two WBX daughterboards.  Is it possible to use 4
> independent RX antennas (all tuned to the same frequency) with this hardware
> setup?
> Specifically, here's what I'm trying to achieve:
> Antenna 0 -> Side A WBX, RX/TX port -> ADC0 -> DDC0I
> Antenna 1 -> Side A WBX, RX2 port -> ADC1 -> DDC1I
> Antenna 2 -> Side B WBX, RX/TX port -> ADC2 -> DDC2I
> Antenna 3 -> Side B WBX, RX2 port -> ADC3 -> DDC3I
> 
> I am trying to modify gnuradio-examples/python/multi-antenna/multi_fft.py to
> make this happen.  I've got it running, but I can't seem to get the WBXs to
> use the antennas connected to their RX2 ports.
> 
> Thanks,
> Scott
> <address@hidden>
> 
> 
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> 
>  No, you will not be able to make that work.  There are *not* two
> independant Rx paths within
>  the WBX, only two different antenna ports, which you can switch the Rx
> chain between, but there
>   is only 1 Rx chain.
> 
> -- 
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortium
> http://www.sbrac.org