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[Discuss-gnuradio] UHD GRC loopback glitches

From: Marc Epard
Subject: [Discuss-gnuradio] UHD GRC loopback glitches
Date: Fri, 17 Sep 2010 15:16:44 -0500

I have a simple GRC flowgraph that transmits a complex sine wave on a UHD USRP2 with a WBX, receives on a USRP2 with a DBSRX, and displays the output on a scope. The two boxes are connected via a 30dB Mini-Circuits attenuator. Mostly the output looks as I expected, but every 350 microseconds or so there's a glitch that looks like the receiver stops and starts. You can see the effect in the screen capture below (or in the PNG at https://public.me.com/mepard in the gnuradio folder, where you'll also find the flowgraph).

I'm using current UHD and gnuradio code via git on a very capable machine running Ubuntu 10.04. System Monitor shows one CPU at 100%, one at 25 - 40% and the others blow 25%. Wireshark shows a lot of activity on the control port for the receiver, but I haven't deciphered the packets (anyone have a UHD Dissector?).

Any idea what is causing this or how I should troubleshoot it?



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