[USRP-users] E312 Multi-channel issues

Beeman, Isaac L. ilbeeman at wpi.edu
Thu Jan 23 21:24:25 EST 2020


Hello everyone,

Sorry for the double message in the same thread, but I thought I would add some of the things I discovered since yesterday in case anyone takes a look at this thread.

First, it appears that I am not the only person to have this issue: http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2019-December/061209.html It looks like a user on the N310 has a similar issue with multi-channel capturing. That led me to believe that I was setting the gain wrong.

Second, it turns out I was setting the gain wrong. When I rewrote my code (featured in the pastebin link from my last post), I forgot to use
_usrp->set_rx_gain(rx_gain, channel_nums[ch]);
instead of
_usrp->set_rx_gain(rx_gain);

Even weirder is that in my old code I didn't make this mistake and somehow got a very similar problem with multichannel gain. I even went as far as to setting the gain on each channel individually to try and reduce errors from trying to do too many things with my refactored code. I'll go back through my old code tomorrow to see if the same gain issue still exists there too.

But the big takeaway is that I solved the gain issue from my previous post and require no further help on this issue.

Isaac Beeman

________________________________
From: USRP-users <usrp-users-bounces at lists.ettus.com> on behalf of Beeman, Isaac L. via USRP-users <usrp-users at lists.ettus.com>
Sent: Wednesday, January 22, 2020 7:19 PM
To: usrp-users at lists.ettus.com <usrp-users at lists.ettus.com>
Subject: [EXT] [USRP-users] E312 Multi-channel issues

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://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fimgur.com%2FEtzLjPO&data=02%7C01%7Cilbeeman%40wpi.edu%7C67d0b1bf68e547772c0008d79f9a0be3%7C589c76f5ca1541f9884b55ec15a0672a%7C0%7C0%7C637153356297733935&sdata=yvQJv03jeiJ0QVI%2BSyIqV4oKSLbOo0gPIdyEZQlKD38%3D&reserved=0 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://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpastebin.com%2FMNmV0CVM&data=02%7C01%7Cilbeeman%40wpi.edu%7C67d0b1bf68e547772c0008d79f9a0be3%7C589c76f5ca1541f9884b55ec15a0672a%7C0%7C0%7C637153356297733935&sdata=s%2BDDjN%2B9wOj3ajYekHjociRSWFURPnrIGJ7%2FPNGOzb4%3D&reserved=0

Isaac Beeman

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