4 RX with 2 WBXs?

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
[email protected]

On Fri, Sep 10, 2010 at 12:04 PM, Scott S. [email protected]
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

gnuradio-examples/python/multi-antenna/multi_fft.py to make this
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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.

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?

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?

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?

Thanks,
Scott
[email protected]

On Fri, Sep 10, 2010 at 3:19 PM, Jason A. [email protected] wrote:

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 [email protected]
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
[email protected]


Discuss-gnuradio mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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.

Hi Jason,

First question what are you tring to do, receive or/and transmitt?
Second: Why is 4 (2TX x 2RX) antennas needed if I understood you
correctly?

If you have two USRP(N)'s, I’d connect them to two different machines.
You can connect both USRP’s to the same if you got a robust machine.

Tell us a little (alot) more about your attempts…

Patrik
----- Original Message -----
From: Scott S.
To: Jason A.
Cc: [email protected]
Sent: Friday, September 10, 2010 22:59
Subject: Re: [Discuss-gnuradio] 4 RX with 2 WBXs?

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?

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?

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?

Thanks,
Scott
[email protected]

On Fri, Sep 10, 2010 at 3:19 PM, Jason A. [email protected] wrote:

On Fri, Sep 10, 2010 at 12:04 PM, Scott S. <[email protected]> 

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 [email protected]
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
<[email protected]>

_______________________________________________Discuss-gnuradio mailing
[email protected]://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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 L.Principal InvestigatorShirleys Bay Radio Astronomy
Consortiumhttp://www.sbrac.org



Discuss-gnuradio mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

If the signals you want to receive are sufficiently close to each other,
you could tune the WBX in the middle and use two independent DDC to
receive two signals with one WBX …

(I’m not mistaken …)

Cheers,

Sylvain

On Fri, Sep 10, 2010 at 03:59:34PM -0400, Scott S. 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.

On Fri, Sep 10, 2010 at 5:11 PM, Jason A. [email protected] wrote:

sample a
Thanks, I’ll definitely try to use the internal switching, but I’m not sure
if it’ll work for my application–my original goal was to measure
relative
phase and amplitude of antenna 1 vs 2, 3, 4.
Looking at the schematics, I see that the several of the WBX’s unused
io_rx/tx signals (io_rx[15:14] and io_tx[15:8]) are available on the
simple_gdb’s J15. Am I on thre right track? If so, that will be
perfect.
Marcus mentioned that GPIO support was “spotty” though. From the USRP
FAQ
page on FPGA registers (
http://gnuradio.org/redmine/wiki/gnuradio/UsrpFAQFpgaRegs) it seems like
it
would be straighforward to toggle two of the pins to control the
commutator. Is there something I’m missing?

You would also need 4 separate Gigabit ethernet ports on your host PC.
Then, you will have 25Msps from each receiver.

That sounds good, but I’m afraid I don’t have the budget for that much
hardware on this project. I can afford another USRP and 2 more WBXs
though. Can you tell me how close would that get me to my goal of 4
coherenet receivers if I use the first USRP as the reference for the
second?
From what I’ve read, it sounds like the 4 PLLs will not drift relative
to
each other, but that there will be random phase offsets that must be
calibrated out after each tune? If so, that would be fine as I already
need
to do a calibration before each data collect to account for other
sources of
phase offset.
The signal I’m trying to measure is less than 200 kHz bandwidth, so I
can
afford to decimate by 128 in the USRP. Hopefully this means that USB
bandwidth won’t be a problem even with two USRPs on the same PC?

Thanks,
Scott

On Fri, Sep 10, 2010 at 09:38:06PM -0400, Scott S. wrote:

generate
http://code.ettus.com/redmine/ettus/projects/public/documents
would be straighforward to toggle two of the pins to control the
commutator. Is there something I’m missing?

You are on the right track here. I think the statement about GPIO
support being spotty is an artifact of possible bit-rot in the gr-gpio,
but for your use case, I would just make your own version of the wbx
daughterboard code in: /usrp/host/lib/db_wbxng.cc

If you could clarify your application a little bit, someone here might
be able to help you be more clever in using the existing antenna
switching and a single USRP to fit your application. Does it need to be
a measurement of three antennas (which can be switched) vs one fixed
reference antenna?

and a GPSDO to supply 10MHz Refclock and PPS signals to all the USRP2’s.
to do a calibration before each data collect to account for other sources of
phase offset.
The signal I’m trying to measure is less than 200 kHz bandwidth, so I can
afford to decimate by 128 in the USRP. Hopefully this means that USB
bandwidth won’t be a problem even with two USRPs on the same PC?

So, in principle, with a clock modification to share the same reference
clock between two USRPs, and two independent USB busses, you may be
getting close to what you need. At decimation 128, you would have the
bandwidth on the USB bus for your four simultaneous receive, but others
may have better insight about the practicality of multiple USRPs on one
USB bus. Also, with a shared reference clock, the WBX PLLs will not
drift
relative to each other once they are locked.

From there, consider the following:

You may need to consider the USRP timestamp fpga work from Eric
Schneider in order to time-align the samples from two separate USRPs:
http://lists.gnu.org/archive/html/discuss-gnuradio/2010-09/msg00012.html

and you will still need some way of setting the timestamp clocks on both
USRPs simultaneously.

You may need to think carefully about not using fractional-N in the WBX
or resetting the fractional divider state synchronously on two USRPs.
You might wish to modify the WBX daughterboard code to turn off the
frac-n divider and stick to integer-n.

You may need to consider the refclock R divider states on the two WBXs,
but you indicate that the phase offset is something you might be able to
calibrate out after each tune.

Hopefully we can discuss your application further here and see if there
is a way to keep it on one USRP to limit some of the extra work

Jason

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