[USRP-users] TwinRX tuning timing

Eugene Grayver eugene.grayver at aero.org
Fri Jul 14 16:22:53 EDT 2017


Yes, I definitely agree that there’s no way to tell when the tuning is DONE.  However, my question was about the ‘shortly after’ part.  Should it not be inserted ‘shortly before’, or ‘exactly at’?  Since there’s typically no way to look into the future, (yes, of course it is doable), there’s no way for somebody to know that the samples that are before the tag are actually ‘invalid.’

_______________________
Eugene Grayver, Ph.D.
Aerospace Corp., Sr. Eng. Spec.
Tel: 310.336.1274
________________________

From: mleech at ripnet.com [mailto:mleech at ripnet.com]
Sent: Friday, July 14, 2017 12:34 PM
To: Eugene Grayver <eugene.grayver at aero.org>
Cc: usrp-users at lists.ettus.com
Subject: Re: [USRP-users] TwinRX tuning timing


The frequency tag is inserted at some point shortly after the command-set is issued to the hardware.  There's no way for the various bits and pieces to tell when the underlying (mostly analog) hardware has converged to an "acceptable" steady-state operating mode.  PLL synthesizers don't instantly switch from one frequency to another, digital (and analog) filters have group delays, etc.

The time to achieve steady-state can vary from hardware-type to hardware-type, ambient temperature, size of the frequency step, etc.






On 2017-07-14 15:10, Eugene Grayver via USRP-users wrote:
I am running some experiments to understand the timing of TwinRX tuning.  A very simple experiment shows that the tag indicating a frequency change is not placed at the right sample.  Here’s a capture: The dashed line indicates the tag sample number.  However, there’s clearly something happening before the tag.  Note that I am not using timed commands for this – just a regular tune request.

[cid:image001.png at 01D2FCA4.4A2FAC00]

_______________________
Eugene Grayver, Ph.D.
Aerospace Corp., Sr. Eng. Spec.
Tel: 310.336.1274
________________________


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