[USRP-users] E312 Multi-channel issues

Beeman, Isaac L. ilbeeman at wpi.edu
Wed Jan 22 19:19:40 EST 2020


Hello Group,

I am using the E312 to receive on both channels so I can use a dual antenna system to determine the direction the received signal is coming from. I have gotten the GPS, internal IMU working, and single channel RX working. The issue is, when I try to receive on both channels simultaneously, one of the receivers (at random?) is measuring about 20db below the other. Here is a photo of what I mean (https://imgur.com/EtzLjPO shows RX-B being the strong signal) and here is a few lines of data from a different test (showing RX-A as the strong signal):

sample#,i1,q1,i2,q2
151,0.372131,0.705048,0.001709,0.003204
152,0.376495,0.702332,0.001862,0.003296
153,0.378906,0.699188,0.001770,0.003204
154,0.387146,0.695160,0.001892,0.003265
155,0.391083,0.692047,0.001740,0.003235
156,0.394806,0.689056,0.001740,0.003204
157,0.399719,0.685974,0.001984,0.003143
158,0.400391,0.683411,0.001984,0.003082
159,0.405457,0.679901,0.001892,0.003082
160,0.408569,0.676788,0.002045,0.003113
161,0.412811,0.673248,0.001984,0.003052
162,0.419006,0.669006,0.002106,0.003143
163,0.420746,0.666077,0.001953,0.003204
164,0.425323,0.662445,0.001892,0.003082
165,0.429535,0.659180,0.002075,0.003082

I have tried everything I can think of: swap out antennas, swap out USRPs, try a wired test, and try different versions of UHD; but found no solution. I even tried directly adjusting for the gain difference, but that just led to a channel with significantly more noise than the other. 

All my code is based off of sample code like rx_multi_samples.cpp and rx_samples_to_file.cpp, so I know that there aren't any glaring issues with my code. I also know that it isn't a direct hardware issue because both RX-A and RX-B receive fine on their own and seem to be randomly selected to be the channel receiving at full power when doing multi-channel.

Am I doing something completely wrong? I can't think of anything else to try. I was hoping to test this out in the next couple weeks, so any help would be greatly appreciated.

Here is a pastebin of my simplified code: https://pastebin.com/MNmV0CVM 

Isaac Beeman



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