[USRP-users] Phase Alignment of Multiple X310s

Rob Kossler rkossler at nd.edu
Tue Nov 7 12:32:13 EST 2017


Yes, y0 and  y1 on first motherboard, y2 and y3 on second motherboard.
Unfortunately, I don't know of any options to improve it.

Rob

On Tue, Nov 7, 2017 at 11:28 AM, ROBIN TORTORA <tilla at comcast.net> wrote:

> On the UBX results, Y0 -> Y1, I assume that is in the same motherboard?
>
>
> Y2 and Y3 on a different motherboard (delta seems to be much larger, but
> very very similar across Y2 and Y3 relative to Y0)?
>
>
> So if I wanted to improve on the "error" on channels 3 and 4 or add more
> channels, are there any options?
>
>
> Lets assume I have done the easy things like match cable lengths and use
> splitters with low phase balance etc. :)
>
> On November 6, 2017 at 6:33 PM Rob Kossler via USRP-users <
> usrp-users at lists.ettus.com> wrote:
>
> Sarah,
> I just happen to be in the middle of an evaluation presently of the
> channel-to-channel phase coherence among various 4 chan receivers, among
> them an X310/UBX (pair) and X310/TwinRx.  For this test, I inject a CW tone
> (-48 dBm) into a 1:4 power divider which then feeds the four receiver
> channels. I then compute the cross correlation (in 1 msec blocks, zero lag)
> between each of channels 2-4 and channel 1 (arbitrarily selected as the
> reference channel).  The following figure shows the channel-to-channel
> phase variation over a 2 sec window.  The left plots are for the four
> channel X310/TwinRx.  The right plots are for the pair of  X310/UBX
> (appropriately synced).   The 3 plots for each device show channels 2-4 in
> comparison to channel 1.  Note that the TwinRx results show much smaller
> variation (as expected since there is a shared LO).  Also note that for UBX
> results, the variation is much smaller for the two channels that are housed
> in the same X310 (top right plot).  I suspect that the much larger
> variations shown for the 3rd and 4th channels (relative to channel 1) are
> related to a 10 MHz PLL circuit in each X310.  Bottom line is that I see at
> least +/- 1 degree "wobble" in the channel-to-channel phase over time.
> You'll need to determine if this is acceptable for your application.
>
> Rob
>
>
> [image: Inline image 1]
>
>
> On Mon, Nov 6, 2017 at 5:11 PM, Marcus D. Leech via USRP-users <
> usrp-users at lists.ettus.com> wrote:
>
> On 11/06/2017 04:57 PM, Sarah Tran via USRP-users wrote:
>
> Hi everyone!
>
>
>
> I was wondering if anyone knew if it was possible to phase align more than
> 2 X310s (with UBX daughterboard) to form a coherent array? I know that 2x2
> MIMO is possible using a single X310, but I want to be able to sync 4 of
> them. I thought I read somewhere that it was dependent on the
> daughterboard, but I can’t find that thread anywhere.
>
>
>
> Thanks for all the help!
>
> Yes, use an external 10MHz reference and 1PPS source, like the Octoclock,
> or Octoclock-G, or similar.
>
> Also, see this App note:
>
> https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices
>
>
>
>
>
>
>
>
>
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