Yes, that shows bursts of digital data, which is what your tx produces. Use
a smaller FFT size to see more detail in the time domain.

On Sun, Jan 24, 2021 at 4:44 PM Jada Mariano Berenguer <beren...@uci.edu>
wrote:

> So, from my understanding you added a File Sink that took in the USRP
> Source's output to the packet_usrp_tx.grc flowgraph? I tried to recreate
> what you did and opened the file with Inspectrum and a screenshot of the
> results is attached. I'm not sure if this is what you got, or what it
> means. I may be saving it to the File Sink incorrectly, so I attached a
> screenshot of the File Sink parameters as well.
>
> Also, what do you mean by 'What happens if you ignore this and keep
> working' ? Because if I run the packet_usrp.grc flowgraph for a while and
> ignore the U's printing out, it doesn't give me the result that I expect.
> The result that I expect would be similar to the result when running the
> packet_loopback_hier.grc file.
>
> Thanks again for your continued help!
>
> On Sun, Jan 24, 2021 at 12:03 PM Jeff Long <willco...@gmail.com> wrote:
>
>> Best I can tell (recording raw samples from the USRP Source to a File
>> Sink, then viewing it with inspectrum), it works and the single 'U' per
>> burst is spurious. The docs would lead you to believe you shouldn't see
>> this. Nothing stands out as wrong in the GRCs. What happens if you ignore
>> this and keep working?
>>
>> On Sun, Jan 24, 2021 at 1:41 PM Jada Mariano Berenguer <beren...@uci.edu>
>> wrote:
>>
>>> Okay, thanks for the tip. Attached in this email is a flowgraph that
>>> only does TX (packet_usrp_tx.grc). I'll continue to look into the problem
>>> and see if I can find any solutions myself as well, but again I'm pretty
>>> new to GNURadio and USRP. If anyone can help me figure out the problem,
>>> it'd be greatly appreciated!! I've also attached the packet loopback
>>> example using the USRP with both TX and RX (packet_usrp.grc), the original
>>> packet loopback example without USRP (packet_loopback_hier.grc), and the
>>> packet_tx and packet_rx flowgraphs as well.
>>>
>>> On Sat, Jan 23, 2021 at 4:36 AM Jeff Long <willco...@gmail.com> wrote:
>>>
>>>> Recommend you find the simplest flowgraph that demonstrates this
>>>> problem. For example, do TX only. Once you find that minimal case, post the
>>>> actual GRC file somewhere so someone can try it out. It's really difficult
>>>> to look through a bunch of parameters in a screenshot and try to guess
>>>> what's happening, unless it's something really obvious.
>>>>
>>>> On Fri, Jan 22, 2021 at 9:24 PM Jada Mariano Berenguer <
>>>> beren...@uci.edu> wrote:
>>>>
>>>>> Hi again, I have a previous message thread regarding this problem, but
>>>>> I kept forgetting to 'reply all' to include the GNURadio email to keep it
>>>>> on the thread and my questions got kind of disorganized, so I wanted to
>>>>> start fresh with a new one and will make sure to reply all in the future.
>>>>>
>>>>> So, I found a packet_loopback example (under the directory:
>>>>> examples/digital/packet) from this message thread
>>>>> <https://lists.gnu.org/archive/html/discuss-gnuradio/2018-06/msg00254.html>
>>>>>  and
>>>>> it says that I can replace the Channel Model block with the USRP source 
>>>>> and
>>>>> sink blocks to try to send packets over the air (a screenshot of the
>>>>> original packet_loopback example and my modified packet_loopback example 
>>>>> is
>>>>> attached as well). This is exactly what I want to do, but I'm running into
>>>>> some issues with the USRP sink.
>>>>>
>>>>> I believe the problem has to do with the way that the USRP sink is
>>>>> receiving the packets. I believe it deals with 'bursty transmission
>>>>> <https://wiki.gnuradio.org/index.php/USRP_Sink>', and so I specified
>>>>> the USRP sink's 'TSB tag name' parameter to 'packet_len', which is what 
>>>>> the
>>>>> packet_tx block specifies as the length tag name (I've also attached a
>>>>> screenshot of the packet_tx flowgraph). I confirmed that the tag name is
>>>>> 'packet_len' by using the Tag Debug block.
>>>>>
>>>>> Also, I've attached a video link here
>>>>> <https://drive.google.com/file/d/1n8SdwjbZebE4Mf4nufTUUnEALPNR0yDF/view?usp=sharing>
>>>>> of what happens when I run the program. It seems like the USRP receives 
>>>>> the
>>>>> packet here and there because of the short 'bursts' shown on the middle
>>>>> graph. Also, I noticed that there's a 'tG' printed in the terminal window
>>>>> (a screenshot of this is attached as well) when the program is first run.
>>>>> What does this mean? I also know that it's experiencing a lot of 
>>>>> underruns,
>>>>> which is essentially the problem I'm trying to solve. It must do with the
>>>>> way the USRP sink is configured to receive the packets.
>>>>>
>>>>> Are there any other parameters that need to be set?
>>>>>
>>>>> Thanks so much in advance!! I appreciate any help :)
>>>>>
>>>>>
>>>>>

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