[USRP-users] USRP B210 RX channel alignment

Marcus D. Leech mleech at ripnet.com
Mon Sep 29 16:13:49 EDT 2014


On 09/29/2014 04:04 PM, Chris Evans via USRP-users wrote:
> All,
>
> I believe I might be running into the same issue that Stefan Ereth 
> wrote about on 05/02/14 and maybe also what Robert Kossler wrote about 
> on 05/23/14 regarding phase alignment of USRP B210 RX channels. I have 
> a 2:1 splitter feeding both RX ports on the B210 and I'm using code 
> similar to examples/rx_multi_samples.cpp. When I receive data from 
> both channels, there is a seemingly random phase offset between the 
> two sinusoids each time I run the program. However, if I 
> issue_stream_cmd() multiple times in one program, the relative phase 
> between the two received sine waves is the same.
>
> If I use GNURadio to receive on two channels, I consistently get the 
> same relative phase offset. The relative phase offset seen in a 
> GNURadio scope is the same as what I see when chipscoping the outputs 
> of both DDCs.
>
> Using chipscope, I see that with GNURadio, radio_0/run_rx and 
> radio_0/strobe_rx go high at the same time that radio_1/run_rx and 
> radio_1/strobe_rx go high. With my UHD program, one channel starts 
> receiving before the other (and I assume the other one starts 
> streaming at some later time determined by software).
>
> How can I force both channels to receive synchronously?
>
> -- 
> Chris Evans
> Systems Engineer
> Azure Summit Technology, Inc.
> 3050 Chain Bridge Road, Suite 600
> Fairfax, VA 22030
> 919-428-6243 (cell)
>
>
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
I would recommend you look at the way gr-uhd commences streaming on a 
multi_usrp object--it does some timed streaming, which will likely 
arrange for things to start at more-or-less the same time.


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