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Re: [USRP-users] daughter board coherency on N310

From: Cameron Matson
Subject: Re: [USRP-users] daughter board coherency on N310
Date: Sun, 22 Nov 2020 09:30:43 -0600


Yes it was all coming out of the same uhd_source object.  I think I was able to resolve the issue for now by setting the "Sync" parameter to "unknown PPS" which I believe is using the White Rabbit Ethernet based timing synchronization which we have connected at one of the SFP ports, though I need to dig in a bit more into the API.

I agree 20 ms is *HUGE*; is it unexpected even without an external timing source?  Should I still be concerned?


On Fri, Nov 20, 2020 at 12:43 PM Marcus D. Leech <patchvonbraun@gmail.com> wrote:
On 11/20/2020 11:49 AM, Rob Kossler wrote:
Hi Cameron,
Yes, this is possible.  I'm not too familiar with gnuradio but in the end you need to use a "timed start" to the receive streams.  

On Fri, Nov 20, 2020 at 7:34 AM Cameron Matson via USRP-users <usrp-users@lists.ettus.com> wrote:
Hello all,

I'm trying to implement a MIMO receiver using the 4 RF chains of the N310.  To test the timing of the system, at the transmitter I'm simply sending a short pulse from one transmit antenna of one USRP.  At the receiver it looks like there is up to a ~20 ms delay/offset between the pairs of antennas 0/1 and 2/3 and that this delay changes each time I restart my GNURadio flowgraph.  I can see the delay both in GNURadio GUI Time Sink and in actual samples that I write to file.  I've tried various pulse widths and sampling rates at both the tx and rx, and it seems invariant to these.

I'd really like to be able to synchronize the 4 RF chains in time simultaneously.  Is that possible?

Cameron Matson


Can you share a simple Gnu Radio flow-graph that displays this behavior?  A 20ms offset is *HUGE*.   Are all 4 streams being streamed out
  of the same uhd_source object?

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