[USRP-users] signal level oscilation at the beginning of burst

Jie Song JSong at availink.com
Thu Jul 27 08:55:53 EDT 2017


Hi Julian,

Thanks a lot for your explanation and I would agree with you, though I am more digital than analog guy.
One more piece of information: 
The signal variations at the beginning of each burst in my tone signal case is actually some DC offset whose level goes down gradually. It lasts about 1ms. 
This could be caused by some initialization of analog front end TDD switch from RX to TX mentioned by Analog Device website somewhere. And it is mentioned that the initialization transition time could be reduced by some GPIO control which I don't fully understand yet.

Cheers,
Jay


-----Original Message-----
From: Julian Arnold [mailto:julian at elitecoding.org] 
Sent: Thursday, July 27, 2017 7:59 AM
To: Jie Song; usrp-users at lists.ettus.com
Subject: Re: [USRP-users] signal level oscilation at the beginning of burst

Hey Jie,

I'm only guessing here but I think what you  are seeing are the effects of using a real-world system with non-ideal frequency response with a signal that has very high frequency content (due to short rise and fall times of the pulses).
Attached you see a simulation of a pulse source with very short rise and fall times connected to an LC series circuit.
The blue trace is showing the output of the pulse source and the green trace is showing the signal after the inductor.
If you were to apply some sort of pulse-shaping to your signal, as you would normally do in a communication system, you probably would not see those oscillations any more.

Cheers,
Julian

On 07/24/2017 10:36 PM, Jie Song via USRP-users wrote:
>
> Hi,
>
>  
>
> I am modifying the “txrx_loopback_to_file” example on B210 to make the 
> TX signal burst.  The TX and RX gains are configured manually at fixed 
> value, but the received signal level has some oscilation the at the 
> beginning of each burst.  Could anybody explain why this happens 
> please?  The figure below shows the problem:
>
>  
>
> Thanks a lot,
>
> Jie
>
>  
>
>  
>
>  
>
>
>
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

--
Julian Arnold, M.Sc.

Institute for Networked Systems
RWTH Aachen University

Kackertstrasse 9
52072 Aachen
Germany



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