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Re: packet_loopback_hier OTA problem

From: Marcus Müller
Subject: Re: packet_loopback_hier OTA problem
Date: Wed, 7 Jul 2021 21:19:21 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

500 kS/s is *really* low for the USRP B2xx. Can you try with 1MS/s? (The CPU 
load is very

Also, regarding your RX gain: have you verified with e.g. a time sink directly 
attached to
the USRP Source that the amplitudes are as you expect them to be? Something 
with a
magnitude value ranging up to 0.1 would be optimal, I guess.

Best regards,


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On 07.07.21 20:51, jack houston wrote:
> htop: https://imgur.com/a/jgzo3Gk <https://imgur.com/a/jgzo3Gk>
> flowgraph: https://imgur.com/a/2XN4Z35 <https://imgur.com/a/2XN4Z35>
> I included a picture of the topology just incase I've missed anything glaring 
> with it,
> although I did not change much at all to the example. I should note that this 
> is the
> first time I have seen any activity on the correlation graph, as well as the 
> HPD parser
> error, which I believe occurs when something is wrong with a packet. The CPU 
> load looks
> fine so is this a bug I'm dealing with? I had prior issues with this example 
> on 3.8 and
> 3.9, and even have done a complete fresh linux install since then.
> On Wed, Jul 7, 2021 at 12:22 PM jack houston <jack.hoston@gmail.com
> <mailto:jack.hoston@gmail.com>> wrote:
>     When running the packet loopback example, from version 3.10, it works as 
> expected
>     without SDR involvement. However when using an SDR sink and source I have 
> no luck
>     with it working. I have tried using different configurations of sdrs, 
> frequencies
>     and gain values all known to be working on other topologies. As an 
> example, I can
>     use my Ettus B205 on a OFDM packet topology using BPSK and can correctly 
> send and
>     receive packets bar some padding issues. Using the same UHD with similiar 
> bit rate
>     and gain values on the packet_loopback_hier example yields nothing.
>     The only error I that I've received is a ursp sink underflow error which 
> should be
>     irrelevant. Included is a link of a screenshot of the example file 
> running. I was
>     told by a colleague that the example has been broken for a while, but if 
> it works
>     under simulation I don't believe thats the case. From what I can tell 
> something is
>     not correctly working on the RX side of the topology, either at the PCS 
> or the HPD.
>     If someone has any knowledge about the example file and what could be 
> causing it to
>     not work in my case, I would be delighted to hear about it.
>     File running: https://imgur.com/a/orVuSZ5 <https://imgur.com/a/orVuSZ5>

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