[USRP-users] USRP B210 RX channel alignment

Chris Evans chris.evans at azuresummit.com
Mon Sep 29 16:04:51 EDT 2014


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)
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